Load Cable Sizing — help

Edition and voltage-change convention: The calculation uses the AS/NZS 3008.1.1:2017 tables, the only supported edition; any other edition is rejected with a validation error. For lagging power factor the effective term is \(R PF + X\sqrt{1-PF^2}\); for leading power factor it is \(R PF - X\sqrt{1-PF^2}\). The signed result reports voltage drop or rise, while compliance uses its absolute magnitude.

Overview

Comprehensive load cable sizing calculator performing seven verification checks per AS/NZS 3008.1.1:2017 and AS/NZS 3000:2018. The calculator determines whether a selected cable is suitable for a given three-phase non-motor load by verifying:

Check 1 — Current Carrying Capacity (CCC): Base ampacity from AS/NZS 3008 tables derated for ambient temperature, circuit grouping, burial depth, soil resistivity, and ground temperature.
Check 2 — Voltage Drop (VD): Three-phase voltage drop at the design current must remain within the allowable percentage.
Check 3 — Short Circuit Withstand (SC): Cable must withstand the prospective fault current for the protection device clearing time (adiabatic equation).
Check 4 — Earth Fault Loop Impedance (EFL): Earth fault current must be sufficient to operate the protection device within the required disconnection time.
Check 5 — Overload Coordination: The protective device rating must lie between the design current and the derated cable capacity, \(I_B \le I_N \le I_Z\) (AS/NZS 3000 Clause 2.5.3.1), so the device protects the cable against overload.
Check 6 — Earth Conductor Size: The protective earth conductor must not be smaller than the AS/NZS 3000 Table 5.1 minimum for the phase conductor size. In automatic mode the earth is chosen as that minimum, so it passes by construction.
Check 7 — Earth Conductor Withstand: The earth conductor must carry the largest earth-fault current — a fault at the cable origin, limited by the source impedance alone — for the earth-fault clearing time \(t_{ef}\) (adiabatic equation, Table 52 \(k\)).

A cable passes overall only when all seven checks pass. Use this calculator for non-motor loads such as control panels, distribution boards, VSD supply cables, lighting boards, HVAC equipment, UPS systems, heating, and welding loads on low-voltage three-phase systems (0.6/1 kV cables).

Two input modes are supported: specify the load by power rating (kW, W, or HP with power factor) or by direct current rating (amps). Unlike the motor cable sizing calculator (c0006), there is no motor efficiency term and the design factor is configurable (default 1.0) rather than the fixed 1.25× used for motor circuits.

Input Parameters

Load Parameters

Parameter	Type	Default	Range	Description
`specify_by`	Enum: power / current	power	—	Specify load by power rating or direct current
`power`	Number	90	0.1 – 10000	Load rated power (active power). Used when specify_by = power.
`powertype`	Enum: kW / watt / HP	kW	—	Power unit. Used when specify_by = power.
`voltage`	Enum	400 V	230 – 690 V	Three-phase line-to-line supply voltage (230, 400, 415 or 690 V; the 0.6/1 kV cable tables do not cover HV — use the HV Cable Sizing calculator above 1 kV)
`powerfactor`	Number	0.85	0.5 – 1.0	Load power factor (cos φ). Used when specify_by = power.
`load_current`	Number	100 A	0.1 – 10000 A	Full load current. Used when specify_by = current.
`load_type`	Enum	General Load	—	Type of load: General Load, Control Panel, Distribution Board, VSD Supply, Lighting Board, HVAC, UPS, Heating, Welding
`design_factor`	Number	1.0	0.8 – 2.0	Multiplier applied to load current for design margin. Unlike motor circuits (fixed 1.25×), this is user-configurable.

Cable

Parameter	Type	Default	Range	Description
`cable_type`	Enum: Fixed / Flexible / MIMS	Fixed	—	Cable construction type
`cable_formation`	Enum: Multicore / Singlecore	Multicore	—	Conductor formation
`conductor`	Enum	50 mm²	1 – 630 mm²	Phase conductor cross-sectional area
`multicore_arrangement`	Enum: Circular / Shaped	Circular	—	Multicore cable arrangement (visible when cable_formation = Multicore)
`singlecore_arrangement`	Enum: Trefoil / Flat	Trefoil	—	Singlecore cable arrangement (visible when cable_formation = Singlecore)
`cable_insulation`	Enum: XLPE / PVC / EPR	XLPE	—	Insulation material type
`metal`	Enum: Cu / Al	Cu	—	Conductor material (hidden when cable_type = MIMS)
`earth_conductor`	Enum	50 mm²	1 – 630 mm²	Protective earth conductor size (defaults to phase conductor size); Check 6 fails when it is below the AS/NZS 3000 Table 5.1 minimum and Check 7 when it cannot withstand the earth-fault current

Cable Installation

Fields in this section are conditionally visible based on the selected installation method and cable formation.

Parameter	Type	Default	Visible When	Description
`installation_method`	Enum	Unenclosed	Always	Unenclosed, DirectBuried, Enclosed, Conduit, BuriedConduit, ThermalInsulation
`unenclosed_type_mc`	Enum	Spaced from Surface	Unenclosed + Multicore	Exposed To Sun, Spaced from Surface, Touching Surface
`unenclosed_type_sc`	Enum	Spaced from Surface & Trefoil or Flat Touching	Unenclosed + Singlecore	Singlecore unenclosed arrangement options. “Conductors Spaced” is rejected: Table 30 gives single-core reactance only for trefoil and flat touching
`unenclosed_in_air`	Enum	Perforated Trays Horizontal	Unenclosed (not touching)	Tray/ladder/catenary arrangement
`unenclosed_catinerary`	Enum	Bunched on Catinerary Wire	Air = On Catinerary Wire	Spaced or Bunched on catenary
`cables_per_tier`	Enum: 1–9	1	Unenclosed + MC + not bunched	Number of multicore cables per tier
`circuits_per_tier`	Enum: 1–3	1	Unenclosed + SC + not bunched	Number of singlecore circuits per tier
`ladder_spacing`	Enum: Touching / Spaced / Bunched	Spaced	Unenclosed + not catenary	Spacing on ladder/tray
`ladder_tiers`	Enum: 1Tier / 2Tier / 3Tier	1Tier	Ladder spacing ≠ Bunched	Number of ladder tiers
`bunched_circuits_cables`	Enum: 1–>18	1	Unenclosed + MC	Number of bunched cables/circuits
`bunched_unenclosed_type`	Enum	Bunched In Air	Unenclosed + MC	Bunched arrangement type
`thermal_ins_type1`	Enum: Completely / Partial	Completely	ThermalInsulation	Thermal insulation coverage
`thermal_ins_type2`	Enum: Unenclosed / Enclosed	Enclosed	ThermalInsulation	Thermal insulation method
`enclosed_install_type`	Enum	Wiring Enclosure in Air	Enclosed	Wiring Enclosure in Air, Metalic Enclosure in Air
`conduit_spacing`	Enum	Touching	Conduit	Touching, Spaced 0.3m, 0.45m, 0.6m
`sc_conduit_install_type`	Enum: Shared / Dedicated	Shared	Singlecore + Conduit	SC conduit arrangement. “Dedicated” (one conductor per conduit) is rejected: Table 30 gives no reactance for that spacing
`direct_buried_spacing`	Enum	Touching	DirectBuried	Touching, Spaced 0.15m, 0.3m, 0.45m, 0.6m
`buried_circuits_cables`	Enum: 1–12	3	Conduit or DirectBuried	Number of buried circuits/cables
`ambient_temp`	Enum: 15–85 °C	40 °C	Not DirectBuried, not Conduit	Air ambient temperature for derating
`burial_depth`	Enum: 0.5–3+ m	0.8	DirectBuried or Conduit	Depth of burial for underground cables
`soil_ambient`	Enum: 10–40 °C	25 °C	DirectBuried or Conduit	Soil ambient temperature
`soil_resistivity`	Enum: 0.8–3 K·m/W	1	DirectBuried or Conduit	Soil thermal resistivity
`num_circuits`	Integer	1	Always	Number of grouped circuits for derating (1–20)

Protection Parameters

Parameter	Type	Default	Range	Description
`fault_current`	Number	10000 A	100 – 100000 A	Prospective short circuit fault current at load
`protection_time`	Number	0.1 s	0.01 – 5.0 s	Protection device maximum clearing time for the prospective fault (Check 3)
`earth_fault_clearing_time`	Number	0.04 s	0.005 – 5.0 s	Clearing time \(t_{ef}\) of the near-end earth fault (Check 7). That fault is far above the device's instantaneous threshold, so this is its instantaneous operating time; enter the upstream backup time instead if clearance relies on the upstream device
`trip_current`	Number	100 A	1 – 10000 A	Protection device (CB or fuse) rating
`trip_multiplier`	Number	5	3 – 15	Instantaneous magnetic trip multiplier (typically 5–10× I_n)
`source_impedance`	Number	0.1 Ω	0.001 – 10.0 Ω	Source impedance (transformer + upstream cables); sets the earth-fault current at the cable origin for Check 7

Calculation Settings

Parameter	Type	Default	Range	Description
`voltagedropmax`	Number	5%	1 – 10%	Maximum allowable voltage drop percentage

Output Results

Load Currents

Output	Unit	Description
`full_load_current`	A	Full load current (calculated from power or user-specified)
`design_current`	A	Design current (full load current × design factor)

Check 1 — Current Carrying Capacity

Output	Unit	Description
`base_current`	A	Base ampacity from AS/NZS 3008 tables (before derating)
`derating_factor`	—	Combined derating factor (product of all applicable factors)
`derated_current`	A	Derated current capacity \(I_{base} \times f_{derate}\)
`design_current`	A	Design current \(I_{FL} \times f_{design}\)
`utilization_percent`	%	Cable utilisation percentage
`passes`	Boolean	Whether derated capacity ≥ design current

Check 2 — Voltage Drop

Output	Unit	Description
`rc`	Ω/km	Cable resistance per km
`xc`	Ω/km	Cable reactance per km
`impedance`	Ω/km	Cable impedance \(Z_c = \sqrt{R_c^2 + X_c^2}\)
`voltage_drop`	V	Voltage drop in volts at the design current \(I_B = I_{load} imes k_{design}\)
`voltage_drop_percent`	%	Voltage drop as percentage of supply
`passes`	Boolean	Whether \(V_{d\%} \leq V_{d,max\%}\)

Check 3 — Short Circuit Withstand

Output	Unit	Description
`k_factor`	—	Material/insulation k-factor from Table 52
`conductor_area`	mm²	Conductor cross-sectional area
`max_withstand_time`	s	Maximum time cable can withstand the fault current
`protection_time`	s	Protection device clearing time (must be ≤ withstand time)
`passes`	Boolean	Whether \(t_{max} \geq t_{protection}\)

Check 4 — Earth Fault Loop Impedance

Output	Unit	Description
`z_source`	Ω	Source impedance (transformer + upstream cables)
`z_phase`	Ω	Phase conductor impedance for cable length
`z_earth`	Ω	Earth conductor impedance for cable length, \(L\sqrt{R_e^2 + X_e^2}\)
`rc_earth`, `xc_earth`	Ω/km	Earth conductor resistance (Tables 34/35) and reactance (Table 30) at the earth size
`z_loop`	Ω	Total earth fault loop impedance
`fault_current`	A	Prospective earth fault current \(V_{ph} / Z_{loop}\)
`required_fault_current`	A	Minimum current to operate protection device
`passes`	Boolean	Whether \(I_{fault} \geq I_{trip} \times k_{mag}\)

Check 5 — Overload Coordination

Output	Unit	Description
`design_current`	A	\(I_B\), the design current from Check 1
`device_rating`	A	\(I_N\), the protective device rating entered
`derated_current`	A	\(I_Z\), the derated cable capacity; also reported as `max_device_rating`, the largest device the cable may be protected by
`device_utilization_percent`	%	\(I_N / I_Z \times 100\)
`passes`	Boolean	Whether \(I_B \le I_N \le I_Z\)

Check 6 — Earth Conductor Size

Reported as check_earth_size.

Output	Unit	Description
`earth_area`	mm²	Earth conductor used (the entered size, or the Table 5.1 minimum in automatic mode)
`minimum_earth_area`	mm²	AS/NZS 3000:2018 Table 5.1 minimum for the phase conductor size
`utilization_percent`	%	Minimum as a share of the earth size
`passes`	Boolean	Whether \(S_e \geq S_{e,5.1}\)

Check 7 — Earth Conductor Withstand

Reported as check_earth_withstand.

Output	Unit	Description
`fault_current`	A	Earth-fault current at the cable origin, \(I_{ef} = V_{ph} / Z_{source}\)
`k_factor`	—	Table 52 k of the phase conductor, shared by the integral earth core
`min_csa`	mm²	Adiabatic minimum earth size \(I_{ef}\sqrt{t_{ef}}/k\)
`max_withstand_time`	s	Longest time the earth conductor carries \(I_{ef}\), \((k S_e / I_{ef})^2\)
`protection_time`	s	The earth-fault clearing time \(t_{ef}\) used (the `earth_fault_clearing_time` input)
`passes`	Boolean	Whether \(S_e \geq S_{e,min}\)

Overall Result

Output	Type	Description
`all_checks_pass`	Boolean	True only when all seven checks pass
`status`	text	"PASS" or "FAIL"
`num_checks_passed`	Integer	Count of passing checks (0–7)
`num_checks`	Integer	Number of checks run (7)
`failure_reasons`	List	Descriptions of any failing checks

Formulas

Load Current (specify by power)

\[ I_{FL} = \frac{P \times 1000}{\sqrt{3} \times V \times \cos\phi} \]

Where \(P\) is load power in kW, \(V\) is line-to-line voltage, and \(\cos\phi\) is power factor. Unlike the motor current formula, there is no efficiency (\(\eta\)) term because this calculator sizes cables for non-motor loads where the rated power already represents the input power drawn from the supply.

For HP input, multiply by 0.7457 to convert to kW first. For watt input, divide by 1000 to convert to kW.

Design Current

\[ I_{design} = I_{FL} \times f_{design} \]

Where \(f_{design}\) is the user-configurable design factor (default 1.0). This differs from the motor calculator where the design factor is fixed at 1.25 per AS/NZS 3000 Clause 4.7. For non-motor loads, the design factor can be set to account for load growth, diversity, or other project-specific requirements.

Check 1: Current Carrying Capacity

\[ I_{derated} = I_{base} \times F_{derating}, \qquad F_{derating} = \prod f_i \]

\(I_{base}\) is the tabulated rating for the chosen cable and installation (AS/NZS 3008.1.1 Tables 4–15) and every factor \(f_i\) is read from the derating table the rating column points to. The report lists each factor with its table, column and row so the product can be checked line by line.

\[ I_{derated} \geq I_{design} \implies \text{PASS} \]

Which derating tables apply

Installation	Grouping	Temperature	Depth	Soil resistivity
Unenclosed, touching a surface; enclosed in air; conduit in air; thermal insulation; bunched on a catenary	Table 22 (bunched circuits)	Table 27(1), air ambient	—	—
Unenclosed single-core on trays, ladders or cleats	Table 23 (circuits per tier, tiers, spacing)	Table 27(1)	—	—
Unenclosed multicore on trays, ladders or cleats	Table 24 (cables per tier, tiers, spacing)	Table 27(1)	—	—
Direct buried	Table 25(1) single-core / 25(2) multicore	Table 27(2), soil ambient	Table 28(1), by conductor size band	Table 29
Buried conduit	Table 26(1) dedicated / 26(2) shared conduits	Table 27(2)	Table 28(2)	Table 29

Temperature factors are taken from the column for the insulation's rated conductor temperature (75 °C PVC, 90 °C XLPE, 110 °C EPR) and equal 1.00 at the tabulated reference ambient of 40 °C in air or 25 °C in the ground. The buried grouping tables start at two circuits: a single buried circuit takes no grouping factor. Ratings marked “exposed to sun” are not tabulated by the standard and are reported as an unsupported combination.

Check 2: Voltage Drop

\[ \Delta V = \sqrt{3} \times I_B \times L_{km} \times \left( R_c \cos\phi \pm X_c \sin\phi \right), \qquad I_B = I_{load} \times k_{design} \]

The drop is evaluated at the design current \(I_B\), the same current the capacity (Check 1) and the protective device (Check 5) are checked against, so a design factor above 1 raises the drop in proportion. \(R_c\) is the AC resistance at the insulation's rated conductor temperature (PVC 75 °C, XLPE 90 °C, EPR 110 °C; aluminium is tabulated only up to 90 °C) from Tables 34–38, and \(X_c\) the reactance for the cable formation and arrangement (Tables 30–32), both in Ω/km. The reactive term is added for a lagging power factor and subtracted for a leading one, so a leading load can show a voltage rise. Compliance uses the magnitude of the change.

\[ V_{d\%} = \frac{|\Delta V|}{V_{LL}} \times 100 \] \[ V_{d\%} \leq V_{d,max\%} \implies \text{PASS} \]

Check 3: Short Circuit Withstand

\[ t_{max} = \frac{k^2 \times S^2}{I_f^2} \]

Adiabatic equation where \(k\) is the conductor/insulation factor (Table 52), \(S\) is conductor CSA in mm², and \(I_f\) is prospective fault current in amps.

\[ t_{max} \geq t_{protection} \implies \text{PASS} \]

k from Table 52

\(k\) is read from AS/NZS 3008.1.1 Table 52 for the conductor metal, the insulation's rated temperature as the initial temperature, and the insulation's short-circuit limit as the final temperature: 160 °C for PVC (140 °C above 300 mm²) and 250 °C for XLPE and EPR. The report quotes the value used; the minimum conductor area \(S_{min} = I_f \sqrt{t} / k\) is shown alongside the withstand time.

Check 4: Earth Fault Loop Impedance

\[ Z_{loop} = Z_{source} + Z_{phase} + Z_{earth} \]

Where \(Z_{source}\) is the transformer/upstream impedance, \(Z_{phase} = L_{km}\sqrt{R_c^2 + X_c^2}\) for the phase conductor, and \(Z_{earth} = L_{km}\sqrt{R_e^2 + X_e^2}\) for the earth conductor. \(R_e\) is the Table 34/35 resistance and \(X_e\) the Table 30 reactance at the earth conductor's size, read for the phase cable's formation and arrangement. All resistances are at the insulation operating temperature (PVC 75 °C, XLPE 90 °C, EPR 110 °C; aluminium capped at 90 °C).

\[ I_{fault} = \frac{V_{ph}}{Z_{loop}} = \frac{V_{LL} / \sqrt{3}}{Z_{loop}} \] \[ I_{fault} \geq I_{trip} \times k_{mag} \implies \text{PASS} \]

The earth fault current must exceed the protection device magnetic trip threshold (\(I_{trip} \times k_{mag}\)) to ensure automatic disconnection within the required time. The impedance magnitudes are added arithmetically, an upper bound on their phasor sum. Neither the conductor temperature rise during the fault nor a supply voltage factor is applied, so compare the margin with the device's tolerance and the loop limits of AS/NZS 3000 Appendix B where the run is close to \(L_{max}\).

\[ L_{max} = \frac{V_{ph} / I_{required} - Z_{source}}{\sqrt{R_c^2 + X_c^2} + \sqrt{R_e^2 + X_e^2}} \]

The longest run for which the same loop model still delivers the required fault current, in km with Ω/km impedances. It is reported for information and agrees exactly with the fault-current check: a run longer than \(L_{max}\) fails, one shorter passes.

Check 5: Overload Coordination

\[ I_B \le I_N \le I_Z \implies \text{PASS} \]

AS/NZS 3000:2018 Clause 2.5.3.1. \(I_B\) is the design current, \(I_N\) the rating of the overload protective device and \(I_Z\) the derated current-carrying capacity from Check 1. A device rated above \(I_Z\) would let the cable run overloaded without tripping; one rated below \(I_B\) would trip on normal load. The companion requirement \(I_2 \le 1.45\,I_Z\) is satisfied by devices complying with AS/NZS 60898, AS/NZS 60947.2 or AS 60269 (gG fuses) and is not evaluated.

Check 6: Earth Conductor Size

\[ S_e \geq S_{e,5.1} \implies \text{PASS} \]

\(S_{e,5.1}\) is the AS/NZS 3000:2018 Table 5.1 minimum copper earth conductor for the phase conductor size (for example 16 mm² for a 50 mm² phase, 25 mm² for 95 mm²). An entered earth below the minimum fails the calculation. Automatic sizing always uses the minimum, so this check passes there and Check 7 decides whether that earth is large enough.

Check 7: Earth Conductor Withstand

\[ I_{ef} = \frac{V_{LL} / \sqrt{3}}{Z_{source}} \] \[ S_{e,min} = \frac{I_{ef} \sqrt{t_{ef}}}{k} \qquad t_{e,max} = \left(\frac{k S_e}{I_{ef}}\right)^2 \] \[ S_e \geq S_{e,min} \implies \text{PASS} \]

The largest earth-fault current flows for a fault at the cable origin, where only the source impedance limits it; a fault further along adds cable impedance and draws less. \(t_{ef}\) is the earth-fault clearing time input (default 0.04 s), not the protection time of Check 3: a near-end earth fault is far above the device's instantaneous threshold, so it clears in the instantaneous operating time. Enter the upstream device's backup time instead if clearance relies on it. The earth is an integral core of the same cable, so it starts at the insulation's operating temperature and ends at the same final temperature as the phase conductor: it shares the phase conductor's Table 52 \(k\). Example: 400 V, \(Z_{source}\) = 0.03 Ω, \(t_{ef}\) = 0.04 s, XLPE copper (\(k\) = 143) gives \(I_{ef}\) = 7698 A and \(S_{e,min}\) = 10.77 mm², so a 10 mm² earth fails and 16 mm² passes. With a 0.1 s backup time the minimum rises to 17.02 mm².

Length Conversion Factors

From	To Meters
1 Kilometer	1000 m
1 Foot	0.3048 m
1 Mile	1609.34 m
1 Yard	0.9144 m

Worked Examples

The 40 examples below were produced by this calculator against the installed AS/NZS 3008.1.1:2017 table data. Every base rating, derating factor, resistance, reactance and k value is quoted with the table it came from, so each line can be checked by hand against the standard. Check 5 applies AS/NZS 3000:2018 Clause 2.5.3.1 to the entered device rating; Check 6 compares the earth conductor with the AS/NZS 3000 Table 5.1 minimum and Check 7 its adiabatic withstand of the earth-fault current at the cable origin for the earth-fault clearing time. Voltage drop is evaluated at the design current, and the earth-fault loop includes the earth conductor's Table 30 reactance at its own size. The summary table links to the full working for each case.

#	Case	I_design (A)	Cable	I_derated (A)	V_d (%)	t_max (s)	I_fault / I_req (A)	I_N / I_Z (A)	Result
1	90 kW distribution board feeder on a perforated tray	152.8	95 mm² Cu XLPE	275.0	1.32	1.846	1,846 / 1,000	200 / 275.0	CCC VD SC EFL OVL ESZ EWT PASS
2	HVAC unit specified by nameplate current, long run	132.0	35 mm² Cu XLPE	144.0	6.72	0.391	380 / 1,000	125 / 144.0	CCC VD SC EFL OVL ESZ EWT FAIL
3	15 kW lighting board, short run, 1.2 design factor	27.3	10 mm² Cu XLPE	69.3	0.80	0.057	583 / 160	32 / 69.3	CCC VD SC EFL OVL ESZ EWT FAIL
4	250 HP load entered in horsepower	294.7	150 mm² Cu XLPE	375.0	2.58	1.150	2,158 / 2,000	400 / 375.0	CCC VD SC EFL OVL ESZ EWT FAIL
5	7.5 kW control panel entered in watts	12.0	2.5 mm² Cu XLPE	27.0	1.78	0.014	276 / 80	16 / 27.0	CCC VD SC EFL OVL ESZ EWT FAIL
6	200 kW load with a leading power factor	320.8	185 mm² Cu XLPE	428.0	1.76	1.120	2,204 / 2,000	400 / 428.0	CCC VD SC EFL OVL ESZ EWT PASS
7	50 mm² PVC copper cable in conduit	101.9	50 mm² Cu PVC	136.0	1.17	0.308	1,617 / 625	125 / 136.0	CCC VD SC EFL OVL ESZ EWT PASS
8	70 mm² EPR (110 °C elastomer) copper cable	169.8	70 mm² Cu EPR	272.0	2.33	0.379	1,515 / 1,000	200 / 272.0	CCC VD SC EFL OVL ESZ EWT PASS
9	120 mm² aluminium XLPE cable	186.8	120 mm² Al XLPE	256.0	2.54	0.572	1,323 / 1,000	200 / 256.0	CCC VD SC EFL OVL ESZ EWT PASS
10	240 mm² aluminium PVC cable direct buried	271.7	240 mm² Al PVC	343.4	2.81	0.780	2,101 / 1,575	315 / 343.4	CCC VD SC EFL OVL ESZ EWT PASS
11	35 mm² flexible copper cable to a welding set	90.0	35 mm² Cu XLPE	144.0	0.62	0.696	1,944 / 500	100 / 144.0	CCC VD SC EFL OVL ESZ EWT PASS
12	Cable partially surrounded by thermal insulation, unenclosed	42.5	10 mm² Cu XLPE	49.0	1.30	0.057	705 / 250	50 / 49.0	CCC VD SC EFL OVL ESZ EWT FAIL
13	500 kW at 690 V on 300 mm² single-core cables in trefoil	464.9	300 mm² Cu XLPE	766.0	1.38	2.045	6,026 / 3,150	630 / 766.0	CCC VD SC EFL OVL ESZ EWT PASS
14	600 A specified load on 400 mm² single-core cables laid flat	600.0	400 mm² Cu XLPE	899.0	1.32	2.525	5,119 / 3,150	630 / 899.0	CCC VD SC EFL OVL ESZ EWT PASS
15	185 mm² shaped-conductor multicore cable	305.7	185 mm² Cu XLPE	428.0	1.81	1.120	3,006 / 2,000	400 / 428.0	CCC VD SC EFL OVL ESZ EWT PASS
16	Two circuits bunched on a wall surface	93.4	50 mm² Cu XLPE	134.4	1.30	0.511	1,374 / 625	125 / 134.4	CCC VD SC EFL OVL ESZ EWT PASS
17	Six cables per tier on two tiers of perforated tray	127.4	95 mm² Cu XLPE	200.8	1.17	1.846	1,762 / 800	160 / 200.8	CCC VD SC EFL OVL ESZ EWT PASS
18	Three cables touching on a single ladder rack	110.4	70 mm² Cu XLPE	188.6	0.95	1.002	2,161 / 625	125 / 188.6	CCC VD SC EFL OVL ESZ EWT PASS
19	Three circuits bunched on a catenary wire	67.9	35 mm² Cu XLPE	108.0	0.99	0.251	1,183 / 400	80 / 108.0	CCC VD SC EFL OVL ESZ EWT FAIL
20	Two single-core trefoil circuits on a ladder	254.7	120 mm² Cu XLPE	410.0	1.75	0.736	2,388 / 1,575	315 / 410.0	CCC VD SC EFL OVL ESZ EWT PASS
21	Four circuits in a wiring enclosure in air	76.4	50 mm² Cu XLPE	97.9	0.99	0.511	1,460 / 500	100 / 97.9	CCC VD SC EFL OVL ESZ EWT FAIL
22	Single-core cables in a metallic enclosure	203.8	95 mm² Cu XLPE	148.8	1.58	0.461	2,033 / 1,250	250 / 148.8	CCC VD SC EFL OVL ESZ EWT FAIL
23	Three circuits in a conduit in air	50.9	25 mm² Cu XLPE	80.2	0.92	0.128	846 / 315	63 / 80.2	CCC VD SC EFL OVL ESZ EWT FAIL
24	Three multicore cables direct buried, touching	135.8	95 mm² Cu XLPE	202.9	2.34	1.846	1,049 / 800	160 / 202.9	CCC VD SC EFL OVL ESZ EWT PASS
25	Single-core trefoil direct buried at 1.0 m in 1.5 K·m/W soil	373.6	240 mm² Cu XLPE	442.5	2.68	2.945	2,860 / 2,000	400 / 442.5	CCC VD SC EFL OVL ESZ EWT PASS
26	Two multicore cables in separate buried conduits 0.3 m apart	118.9	95 mm² Cu XLPE	225.7	1.92	1.846	1,109 / 800	160 / 225.7	CCC VD SC EFL OVL ESZ EWT PASS
27	Single-core circuit in a shared buried conduit	305.7	240 mm² Cu XLPE	420.9	2.02	2.945	3,006 / 1,575	315 / 420.9	CCC VD SC EFL OVL ESZ EWT PASS
28	Cable completely surrounded by thermal insulation, enclosed	42.5	16 mm² Cu XLPE	34.0	0.83	0.145	1,008 / 250	50 / 34.0	CCC VD SC EFL OVL ESZ EWT FAIL
29	55 °C switchroom ambient	161.3	70 mm² Cu XLPE	186.3	1.39	0.445	2,161 / 1,000	200 / 186.3	CCC VD SC EFL OVL ESZ EWT FAIL
30	25 °C ambient with a PVC cable	34.0	16 mm² Cu PVC	87.1	0.73	0.088	938 / 200	40 / 87.1	CCC VD SC EFL OVL ESZ EWT FAIL
31	Hot, dry soil: 35 °C at 1.5 m depth in 2.5 K·m/W ground	101.9	95 mm² Cu XLPE	189.1	2.20	1.846	862 / 625	125 / 189.1	CCC VD SC EFL OVL ESZ EWT PASS
32	36 kA fault level with a 0.3 s clearing time	152.8	95 mm² Cu XLPE	275.0	1.32	0.142	2,006 / 1,000	200 / 275.0	CCC VD SC EFL OVL ESZ EWT FAIL
33	350 m run on a 160 A type-D breaker	127.4	70 mm² Cu XLPE	230.0	6.38	1.002	483 / 1,600	160 / 230.0	CCC VD SC EFL OVL ESZ EWT FAIL
34	Full-size earth conductor on a long 95 mm² feeder	152.8	95 mm² Cu XLPE	275.0	2.97	1.846	1,877 / 1,000	200 / 275.0	CCC VD SC EFL OVL ESZ EWT PASS
35	Stiff supply: 0.02 Ω source and 25 kA cleared in 50 ms	203.8	120 mm² Cu XLPE	327.0	1.09	0.471	3,164 / 1,250	250 / 327.0	CCC VD SC EFL OVL ESZ EWT PASS
36	300 ft run entered in feet at 415 V	81.8	50 mm² Cu XLPE	182.0	1.43	0.511	1,139 / 500	100 / 182.0	CCC VD SC EFL OVL ESZ EWT PASS
37	Auto-size a 75 kW feeder on a perforated tray	127.4	50 mm² Cu XLPE (auto)	182.0	3.04	0.227	866 / 800	160 / 182.0	CCC VD SC EFL OVL ESZ EWT PASS
38	Auto-size 400 A on aluminium single-core cables	400.0	185 mm² Al XLPE (auto)	427.0	2.25	0.489	3,065 / 2,000	400 / 427.0	CCC VD SC EFL OVL ESZ EWT PASS
39	Auto-size a 30 kW pump-house feeder, 180 m direct buried	50.9	35 mm² Cu XLPE (auto)	121.5	2.42	0.696	398 / 315	63 / 121.5	CCC VD SC EFL OVL ESZ EWT PASS
40	Auto-size 500 kW over 400 m: no single cable passes	801.9	500 mm² Cu XLPE (auto)	794.0	11.04	3.945	1,658 / 5,000	1,000 / 794.0	CCC VD SC EFL OVL ESZ EWT FAIL

Example 1 — 90 kW distribution board feeder on a perforated tray

Baseline case: every check passes with a comfortable margin.

Given: 90 kW distribution board load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 95 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 80 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 200 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 90.00 kW × 1000 / (√3 × 400 × 0.85) = 152.8 A
Check 1 — capacity	Base rating Table 14, column 2, row 95: 275 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 275 × 1.00 = 275.0 A vs I_design 152.8 A (loading 55.6 %) PASS
Check 2 — voltage drop	R_c = 0.248 Ω/km (Table 35), X_c = 0.0725 Ω/km (Table 30). At the design current, ΔV = √3 × 152.8 × 0.080 × (0.248 × 0.85 + 0.0725 × 0.527) = 5.27 V (drop) = 1.32 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 95)² / 10,000² = 1.846 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.080 × √(0.927² + 0.0808²) = 0.0744 Ω. Z_loop = 0.03 + 0.0207 (phase) + 0.0744 (earth) = 0.1251 Ω. I_fault = 400/√3 / 0.1251 = 1,846 A vs 200 × 5 = 1,000 A; L_max = 169 m vs 80 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 152.8 A ≤ 200 A ≤ 275.0 A (device at 72.7 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 95 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 1,390 W (1.54 %)

Example 2 — HVAC unit specified by nameplate current, long run

Specify-by-current mode with a 1.1 design factor: voltage drop (at the 132 A design current) and the earth-fault loop fail, the 125 A device sits below the design current, and the 10 mm² Table 5.1 earth cannot carry the 8 kA near-end earth fault.

Given: 120 A hvac load, 415 V three-phase, design factor 1.1. 35 mm² copper XLPE (90 °C) fixed multicore cable, 10 mm² earth, 200 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 8.0 kA cleared in 0.2 s, earth-fault clearing time 0.04 s, 125 A device with 8× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 120.0 A (specified); I_design = 120.0 × 1.1 = 132.0 A
Check 1 — capacity	Base rating Table 14, column 2, row 35: 144 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 144 × 1.00 = 144.0 A vs I_design 132.0 A (loading 91.7 %) PASS
Check 2 — voltage drop	R_c = 0.669 Ω/km (Table 35), X_c = 0.0786 Ω/km (Table 30). At the design current, ΔV = √3 × 132.0 × 0.200 × (0.669 × 0.85 + 0.0786 × 0.527) = 27.90 V (drop) = 6.72 % of 415 V, limit 5 % FAIL
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 35)² / 8,000² = 0.391 s vs 0.2 s; S_min = 8,000 × √0.2 / 143 = 25.0 mm² PASS
Check 4 — earth fault loop	Earth 10 mm²: R_e = 2.33, X_e = 0.0840 Ω/km (Table 30 at the earth size), Z_earth = 0.200 × √(2.33² + 0.0840²) = 0.4663 Ω. Z_loop = 0.03 + 0.1347 (phase) + 0.4663 (earth) = 0.6310 Ω. I_fault = 415/√3 / 0.6310 = 380 A vs 125 × 8 = 1,000 A; L_max = 70 m vs 200 m FAIL
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 132.0 A ≤ 125 A ≤ 144.0 A (device at 86.8 % of cable capacity) FAIL
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 35 mm² phase conductor: 10 mm²; earth 10 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 415/√3 / 0.03 = 7,987 A. S_e,min = 7,987 × √0.04 (t_ef) / 143 = 11.17 mm² (k as the phase conductor, Table 52) vs 10 mm²; t_max = 0.032 s FAIL
Result	3/7 checks pass → FAIL; governing criterion Earth Fault; power loss 5,780 W (7.88 %). Voltage drop (6.72%) > Maximum allowed (5%); Insufficient fault current: 379.7A < 1000.0A; Cable too long: 200.0m > 69.7m; Device rating (125A) < Design current (132.0A); Earth conductor 10 mm² < 11.2 mm² needed for 7987 A in 0.04 s

Example 3 — 15 kW lighting board, short run, 1.2 design factor

A small cable that carries the load easily but cannot withstand the fault current for the clearing time.

Given: 15 kW lighting board load, PF 0.95 lagging, 400 V three-phase, design factor 1.2. 10 mm² copper XLPE (90 °C) fixed multicore cable, 4 mm² earth, 30 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 35 °C. Protection: prospective fault 6.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 32 A device with 5× instantaneous trip, source impedance 0.15 Ω, voltage-drop limit 5 %.

Load current	I_load = 15.00 kW × 1000 / (√3 × 400 × 0.95) = 22.8 A; I_design = 22.8 × 1.2 = 27.3 A
Check 1 — capacity	Base rating Table 14, column 2, row 10: 66 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 35: 1.05 → F = 1.05. I_derated = 66 × 1.05 = 69.3 A vs I_design 27.3 A (loading 39.5 %) PASS
Check 2 — voltage drop	R_c = 2.33 Ω/km (Table 35), X_c = 0.0840 Ω/km (Table 30). At the design current, ΔV = √3 × 27.3 × 0.030 × (2.33 × 0.95 + 0.0840 × 0.312) = 3.18 V (drop) = 0.80 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 10)² / 6,000² = 0.057 s vs 0.1 s; S_min = 6,000 × √0.1 / 143 = 13.3 mm² FAIL
Check 4 — earth fault loop	Earth 4 mm²: R_e = 5.88, X_e = 0.0930 Ω/km (Table 30 at the earth size), Z_earth = 0.030 × √(5.88² + 0.0930²) = 0.1764 Ω. Z_loop = 0.15 + 0.0699 (phase) + 0.1764 (earth) = 0.3964 Ω. I_fault = 400/√3 / 0.3964 = 583 A vs 32 × 5 = 160 A; L_max = 157 m vs 30 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 27.3 A ≤ 32 A ≤ 69.3 A (device at 46.2 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 10 mm² phase conductor: 4 mm²; earth 4 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.15 = 1,540 A. S_e,min = 1,540 × √0.04 (t_ef) / 143 = 2.15 mm² (k as the phase conductor, Table 52) vs 4 mm²; t_max = 0.138 s PASS
Result	6/7 checks pass → FAIL; governing criterion Short Circuit; power loss 109 W (0.73 %). Insufficient withstand: 0.057s < 0.1s

Example 4 — 250 HP load entered in horsepower

Power in HP is converted to kW (0.7457 kW/HP) before the current is calculated; a 400 A device exceeds the 375 A cable rating, and the earth-fault loop passes with only an 8 % margin.

Given: 250 HP general load, PF 0.88 lagging, 415 V three-phase, design factor 1.0. 150 mm² copper XLPE (90 °C) fixed multicore cable, 50 mm² earth, 120 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 20.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 400 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 186.42 kW × 1000 / (√3 × 415 × 0.88) = 294.7 A
Check 1 — capacity	Base rating Table 14, column 2, row 150: 375 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 375 × 1.00 = 375.0 A vs I_design 294.7 A (loading 78.6 %) PASS
Check 2 — voltage drop	R_c = 0.160 Ω/km (Table 35), X_c = 0.0718 Ω/km (Table 30). At the design current, ΔV = √3 × 294.7 × 0.120 × (0.160 × 0.88 + 0.0718 × 0.475) = 10.71 V (drop) = 2.58 % of 415 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 150)² / 20,000² = 1.150 s vs 0.1 s; S_min = 20,000 × √0.1 / 143 = 44.2 mm² PASS
Check 4 — earth fault loop	Earth 50 mm²: R_e = 0.494, X_e = 0.0751 Ω/km (Table 30 at the earth size), Z_earth = 0.120 × √(0.494² + 0.0751²) = 0.0600 Ω. Z_loop = 0.03 + 0.0210 (phase) + 0.0600 (earth) = 0.1110 Ω. I_fault = 415/√3 / 0.1110 = 2,158 A vs 400 × 5 = 2,000 A; L_max = 133 m vs 120 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 294.7 A ≤ 400 A ≤ 375.0 A (device at 106.7 % of cable capacity) FAIL
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 150 mm² phase conductor: 50 mm²; earth 50 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 415/√3 / 0.03 = 7,987 A. S_e,min = 7,987 × √0.04 (t_ef) / 143 = 11.17 mm² (k as the phase conductor, Table 52) vs 50 mm²; t_max = 0.801 s PASS
Result	6/7 checks pass → FAIL; governing criterion Overload; power loss 5,003 W (2.68 %). Device rating (400A) > Derated capacity (375.0A)

Example 5 — 7.5 kW control panel entered in watts

A small final sub-circuit on a 16 A breaker: 2.5 mm² needs a faster-clearing device at a 3 kA fault level, and its 2.5 mm² earth cannot carry the 2.9 kA near-end earth fault even for 0.04 s.

Given: 7,500 W control panel load, PF 0.9 lagging, 400 V three-phase, design factor 1.0. 2.5 mm² copper XLPE (90 °C) fixed multicore cable, 2.5 mm² earth, 40 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 3.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 16 A device with 5× instantaneous trip, source impedance 0.08 Ω, voltage-drop limit 2.5 %.

Load current	I_load = 7.50 kW × 1000 / (√3 × 400 × 0.9) = 12.0 A
Check 1 — capacity	Base rating Table 14, column 2, row 2.5: 27 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 27 × 1.00 = 27.0 A vs I_design 12.0 A (loading 44.5 %) PASS
Check 2 — voltage drop	R_c = 9.45 Ω/km (Table 35), X_c = 0.0988 Ω/km (Table 30). At the design current, ΔV = √3 × 12.0 × 0.040 × (9.45 × 0.9 + 0.0988 × 0.436) = 7.12 V (drop) = 1.78 % of 400 V, limit 2.5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 2.5)² / 3,000² = 0.014 s vs 0.1 s; S_min = 3,000 × √0.1 / 143 = 6.6 mm² FAIL
Check 4 — earth fault loop	Earth 2.5 mm²: R_e = 9.45, X_e = 0.0988 Ω/km (Table 30 at the earth size), Z_earth = 0.040 × √(9.45² + 0.0988²) = 0.3780 Ω. Z_loop = 0.08 + 0.3780 (phase) + 0.3780 (earth) = 0.8360 Ω. I_fault = 400/√3 / 0.8360 = 276 A vs 16 × 5 = 80 A; L_max = 148 m vs 40 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 12.0 A ≤ 16 A ≤ 27.0 A (device at 59.3 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 2.5 mm² phase conductor: 2.5 mm²; earth 2.5 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.08 = 2,887 A. S_e,min = 2,887 × √0.04 (t_ef) / 143 = 4.04 mm² (k as the phase conductor, Table 52) vs 2.5 mm²; t_max = 0.015 s FAIL
Result	5/7 checks pass → FAIL; governing criterion Short Circuit; power loss 164 W (2.19 %). Insufficient withstand: 0.014s < 0.1s; Earth conductor 2.5 mm² < 4.0 mm² needed for 2887 A in 0.04 s

Example 6 — 200 kW load with a leading power factor

With a leading power factor the reactive term subtracts: R·PF − X·sin φ.

Given: 200 kW general load, PF 0.9 leading, 400 V three-phase, design factor 1.0. 185 mm² copper XLPE (90 °C) fixed multicore cable, 70 mm² earth, 150 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 25.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 400 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 200.00 kW × 1000 / (√3 × 400 × 0.9) = 320.8 A
Check 1 — capacity	Base rating Table 14, column 2, row 185: 428 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 428 × 1.00 = 428.0 A vs I_design 320.8 A (loading 74.9 %) PASS
Check 2 — voltage drop	R_c = 0.129 Ω/km (Table 35), X_c = 0.0720 Ω/km (Table 30). At the design current, ΔV = √3 × 320.8 × 0.150 × (0.129 × 0.9 − 0.0720 × 0.436) = 7.06 V (drop) = 1.76 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 185)² / 25,000² = 1.120 s vs 0.1 s; S_min = 25,000 × √0.1 / 143 = 55.3 mm² PASS
Check 4 — earth fault loop	Earth 70 mm²: R_e = 0.343, X_e = 0.0741 Ω/km (Table 30 at the earth size), Z_earth = 0.150 × √(0.343² + 0.0741²) = 0.0526 Ω. Z_loop = 0.03 + 0.0222 (phase) + 0.0526 (earth) = 0.1048 Ω. I_fault = 400/√3 / 0.1048 = 2,204 A vs 400 × 5 = 2,000 A; L_max = 171 m vs 150 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 320.8 A ≤ 400 A ≤ 428.0 A (device at 93.5 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 185 mm² phase conductor: 70 mm²; earth 70 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 70 mm²; t_max = 1.691 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 5,972 W (2.99 %)

Example 7 — 50 mm² PVC copper cable in conduit

PVC: 75 °C ratings, 75 °C resistance and the lower short-circuit constant k from Table 52.

Given: 60 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 50 mm² copper PVC (75 °C) fixed multicore cable, 16 mm² earth, 60 m; in conduit in air, 1 circuit(s), air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 125 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 60.00 kW × 1000 / (√3 × 400 × 0.85) = 101.9 A
Check 1 — capacity	Base rating Table 13, column 25, row 50: 136 A. Derating Table 22, column 2, row 1: 1.00; Table 27(1), 75 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 136 × 1.00 = 136.0 A vs I_design 101.9 A (loading 74.9 %) PASS
Check 2 — voltage drop	R_c = 0.471 Ω/km (Table 35), X_c = 0.0797 Ω/km (Table 30). At the design current, ΔV = √3 × 101.9 × 0.060 × (0.471 × 0.85 + 0.0797 × 0.527) = 4.68 V (drop) = 1.17 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 111 (Table 52). t_max = (111 × 50)² / 10,000² = 0.308 s vs 0.1 s; S_min = 10,000 × √0.1 / 111 = 28.5 mm² PASS
Check 4 — earth fault loop	Earth 16 mm²: R_e = 1.40, X_e = 0.0861 Ω/km (Table 30 at the earth size), Z_earth = 0.060 × √(1.40² + 0.0861²) = 0.0842 Ω. Z_loop = 0.03 + 0.0287 (phase) + 0.0842 (earth) = 0.1428 Ω. I_fault = 400/√3 / 0.1428 = 1,617 A vs 125 × 5 = 625 A; L_max = 181 m vs 60 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 101.9 A ≤ 125 A ≤ 136.0 A (device at 91.9 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 50 mm² phase conductor: 16 mm²; earth 16 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 111 = 13.87 mm² (k as the phase conductor, Table 52) vs 16 mm²; t_max = 0.053 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 880 W (1.47 %)

Example 8 — 70 mm² EPR (110 °C elastomer) copper cable

EPR uses the 110 °C rating columns, 110 °C resistance and k for a 110 °C initial temperature.

Given: 100 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 70 mm² copper EPR (110 °C) fixed multicore cable, 25 mm² earth, 90 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 15.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 200 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 100.00 kW × 1000 / (√3 × 400 × 0.85) = 169.8 A
Check 1 — capacity	Base rating Table 15, column 2, row 70: 272 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 110 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 272 × 1.00 = 272.0 A vs I_design 169.8 A (loading 62.4 %) PASS
Check 2 — voltage drop	R_c = 0.364 Ω/km (Table 35), X_c = 0.0798 Ω/km (Table 30). At the design current, ΔV = √3 × 169.8 × 0.090 × (0.364 × 0.85 + 0.0798 × 0.527) = 9.30 V (drop) = 2.33 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 132 (Table 52). t_max = (132 × 70)² / 15,000² = 0.379 s vs 0.1 s; S_min = 15,000 × √0.1 / 132 = 35.9 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.984, X_e = 0.0895 Ω/km (Table 30 at the earth size), Z_earth = 0.090 × √(0.984² + 0.0895²) = 0.0889 Ω. Z_loop = 0.03 + 0.0335 (phase) + 0.0889 (earth) = 0.1525 Ω. I_fault = 400/√3 / 0.1525 = 1,515 A vs 200 × 5 = 1,000 A; L_max = 148 m vs 90 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 169.8 A ≤ 200 A ≤ 272.0 A (device at 73.5 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 70 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 132 = 11.66 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.184 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 2,834 W (2.83 %)

Example 9 — 120 mm² aluminium XLPE cable

Aluminium: lower ampacity, higher resistance and k = 94 (Table 52, Al 90 → 250 °C).

Given: 110 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 120 mm² aluminium XLPE (90 °C) fixed multicore cable, 35 mm² earth, 100 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 15.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 200 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 110.00 kW × 1000 / (√3 × 400 × 0.85) = 186.8 A
Check 1 — capacity	Base rating Table 14, column 4, row 120: 256 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 256 × 1.00 = 256.0 A vs I_design 186.8 A (loading 73.0 %) PASS
Check 2 — voltage drop	R_c = 0.325 Ω/km (Table 35), X_c = 0.0713 Ω/km (Table 30). At the design current, ΔV = √3 × 186.8 × 0.100 × (0.325 × 0.85 + 0.0713 × 0.527) = 10.15 V (drop) = 2.54 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 94 (Table 52). t_max = (94 × 120)² / 15,000² = 0.572 s vs 0.1 s; S_min = 15,000 × √0.1 / 94 = 50.2 mm² PASS
Check 4 — earth fault loop	Earth 35 mm²: R_e = 1.11, X_e = 0.0786 Ω/km (Table 30 at the earth size), Z_earth = 0.100 × √(1.11² + 0.0786²) = 0.1113 Ω. Z_loop = 0.03 + 0.0333 (phase) + 0.1113 (earth) = 0.1746 Ω. I_fault = 400/√3 / 0.1746 = 1,323 A vs 200 × 5 = 1,000 A; L_max = 139 m vs 100 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 186.8 A ≤ 200 A ≤ 256.0 A (device at 78.1 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 120 mm² phase conductor: 35 mm²; earth 35 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 94 = 16.29 mm² (k as the phase conductor, Table 52) vs 35 mm²; t_max = 0.185 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 3,402 W (3.09 %)

Example 10 — 240 mm² aluminium PVC cable direct buried

Aluminium PVC underground: Table 25(2), 27(2), 28(1) and 29 all apply.

Given: 160 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 240 mm² aluminium PVC (75 °C) fixed multicore cable, 95 mm² earth, 140 m; direct buried, 1 cable(s)/circuit(s) touching, depth 0.8 m, soil 1 K·m/W at 25 °C. Protection: prospective fault 20.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 315 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 160.00 kW × 1000 / (√3 × 400 × 0.85) = 271.7 A
Check 1 — capacity	Base rating Table 13, column 24, row 240: 344 A. Derating Table 27(2), 75 °C conductor column, row 25: 1.00; Table 28(1), column 3, row 0.8: 0.960; Table 29, column 2, row 1: 1.04 → F = 0.998. I_derated = 344 × 0.998 = 343.4 A vs I_design 271.7 A (loading 79.1 %) PASS
Check 2 — voltage drop	R_c = 0.155 Ω/km (Table 35), X_c = 0.0735 Ω/km (Table 30). At the design current, ΔV = √3 × 271.7 × 0.140 × (0.155 × 0.85 + 0.0735 × 0.527) = 11.23 V (drop) = 2.81 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 74 (Table 52). t_max = (74 × 240)² / 20,000² = 0.780 s vs 0.1 s; S_min = 20,000 × √0.1 / 74 = 85.9 mm² PASS
Check 4 — earth fault loop	Earth 95 mm²: R_e = 0.392, X_e = 0.0766 Ω/km (Table 30 at the earth size), Z_earth = 0.140 × √(0.392² + 0.0766²) = 0.0559 Ω. Z_loop = 0.03 + 0.0240 (phase) + 0.0559 (earth) = 0.1099 Ω. I_fault = 400/√3 / 0.1099 = 2,101 A vs 315 × 5 = 1,575 A; L_max = 204 m vs 140 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 271.7 A ≤ 315 A ≤ 343.4 A (device at 91.7 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 240 mm² phase conductor: 95 mm²; earth 95 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 74 = 20.92 mm² (k as the phase conductor, Table 52) vs 95 mm²; t_max = 0.825 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 4,806 W (3.00 %)

Example 11 — 35 mm² flexible copper cable to a welding set

Flexible cables use the flexible-cable rating column and Tables 37 / 31 for resistance and reactance.

Given: 90 A welding load, 400 V three-phase, design factor 1.0. 35 mm² copper XLPE (90 °C) flexible multicore cable, 10 mm² earth, 25 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 6.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 100 A device with 5× instantaneous trip, source impedance 0.04 Ω, voltage-drop limit 5 %.

Load current	I_load = 90.0 A (specified)
Check 1 — capacity	Base rating Table 14, column 3, row 35: 144 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 144 × 1.00 = 144.0 A vs I_design 90.0 A (loading 62.5 %) PASS
Check 2 — voltage drop	R_c = 0.707 Ω/km (Table 37), X_c = 0.0761 Ω/km (Table 31). At the design current, ΔV = √3 × 90.0 × 0.025 × (0.707 × 0.85 + 0.0761 × 0.527) = 2.50 V (drop) = 0.62 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 35)² / 6,000² = 0.696 s vs 0.1 s; S_min = 6,000 × √0.1 / 143 = 13.3 mm² PASS
Check 4 — earth fault loop	Earth 10 mm²: R_e = 2.44, X_e = 0.0810 Ω/km (Table 30 at the earth size), Z_earth = 0.025 × √(2.44² + 0.0810²) = 0.0610 Ω. Z_loop = 0.04 + 0.0178 (phase) + 0.0610 (earth) = 0.1188 Ω. I_fault = 400/√3 / 0.1188 = 1,944 A vs 100 × 5 = 500 A; L_max = 134 m vs 25 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 90.0 A ≤ 100 A ≤ 144.0 A (device at 69.4 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 35 mm² phase conductor: 10 mm²; earth 10 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.04 = 5,774 A. S_e,min = 5,774 × √0.04 (t_ef) / 143 = 8.07 mm² (k as the phase conductor, Table 52) vs 10 mm²; t_max = 0.061 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 430 W (0.81 %)

Example 12 — Cable partially surrounded by thermal insulation, unenclosed

Partial contact with thermal insulation derates less than complete enclosure (compare Example 28); the fault withstand fails, a 50 A device cannot protect a 49 A cable, and the 4 mm² earth is too small for the near-end earth fault.

Given: 25 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 10 mm² copper XLPE (90 °C) fixed multicore cable, 4 mm² earth, 35 m; partial surrounded by thermal insulation, unenclosed, air ambient 40 °C. Protection: prospective fault 6.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 50 A device with 5× instantaneous trip, source impedance 0.04 Ω, voltage-drop limit 5 %.

Load current	I_load = 25.00 kW × 1000 / (√3 × 400 × 0.85) = 42.5 A
Check 1 — capacity	Base rating Table 14, column 15, row 10: 49 A. Derating Table 22, column 2, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 49 × 1.00 = 49.0 A vs I_design 42.5 A (loading 86.6 %) PASS
Check 2 — voltage drop	R_c = 2.33 Ω/km (Table 35), X_c = 0.0840 Ω/km (Table 30). At the design current, ΔV = √3 × 42.5 × 0.035 × (2.33 × 0.85 + 0.0840 × 0.527) = 5.21 V (drop) = 1.30 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 10)² / 6,000² = 0.057 s vs 0.1 s; S_min = 6,000 × √0.1 / 143 = 13.3 mm² FAIL
Check 4 — earth fault loop	Earth 4 mm²: R_e = 5.88, X_e = 0.0930 Ω/km (Table 30 at the earth size), Z_earth = 0.035 × √(5.88² + 0.0930²) = 0.2058 Ω. Z_loop = 0.04 + 0.0816 (phase) + 0.2058 (earth) = 0.3274 Ω. I_fault = 400/√3 / 0.3274 = 705 A vs 50 × 5 = 250 A; L_max = 108 m vs 35 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 42.5 A ≤ 50 A ≤ 49.0 A (device at 102.0 % of cable capacity) FAIL
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 10 mm² phase conductor: 4 mm²; earth 4 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.04 = 5,774 A. S_e,min = 5,774 × √0.04 (t_ef) / 143 = 8.07 mm² (k as the phase conductor, Table 52) vs 4 mm²; t_max = 0.010 s FAIL
Result	4/7 checks pass → FAIL; governing criterion Earth Withstand; power loss 441 W (1.76 %). Insufficient withstand: 0.057s < 0.1s; Device rating (50A) > Derated capacity (49.0A); Earth conductor 4 mm² < 8.1 mm² needed for 5774 A in 0.04 s

Example 13 — 500 kW at 690 V on 300 mm² single-core cables in trefoil

Single-core trefoil on a ladder: Table 23 grouping and the trefoil reactance column of Table 30.

Given: 500 kW general load, PF 0.9 lagging, 690 V three-phase, design factor 1.0. 300 mm² copper XLPE (90 °C) fixed singlecore cable (trefoil), 120 mm² earth, 110 m; unenclosed, spaced from surface & trefoil or flat touching, on ladder, racks or cleats, 1 circuit(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 30.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 630 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 500.00 kW × 1000 / (√3 × 690 × 0.9) = 464.9 A
Check 1 — capacity	Base rating Table 8, column 2, row 300: 766 A. Derating Table 23, 18 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 766 × 1.00 = 766.0 A vs I_design 464.9 A (loading 60.7 %) PASS
Check 2 — voltage drop	R_c = 0.0803 Ω/km (Table 34), X_c = 0.0809 Ω/km (Table 30). At the design current, ΔV = √3 × 464.9 × 0.110 × (0.0803 × 0.9 + 0.0809 × 0.436) = 9.52 V (drop) = 1.38 % of 690 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 300)² / 30,000² = 2.045 s vs 0.1 s; S_min = 30,000 × √0.1 / 143 = 66.3 mm² PASS
Check 4 — earth fault loop	Earth 120 mm²: R_e = 0.197, X_e = 0.0844 Ω/km (Table 30 at the earth size), Z_earth = 0.110 × √(0.197² + 0.0844²) = 0.0236 Ω. Z_loop = 0.03 + 0.0125 (phase) + 0.0236 (earth) = 0.0661 Ω. I_fault = 690/√3 / 0.0661 = 6,026 A vs 630 × 5 = 3,150 A; L_max = 294 m vs 110 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 464.9 A ≤ 630 A ≤ 766.0 A (device at 82.2 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 300 mm² phase conductor: 120 mm²; earth 120 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 690/√3 / 0.03 = 13,279 A. S_e,min = 13,279 × √0.04 (t_ef) / 143 = 18.57 mm² (k as the phase conductor, Table 52) vs 120 mm²; t_max = 1.670 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 5,726 W (1.15 %)

Example 14 — 600 A specified load on 400 mm² single-core cables laid flat

Flat-touching single-core cables; the report recommends parallel cables above 500 A.

Given: 600 A general load, 415 V three-phase, design factor 1.0. 400 mm² copper XLPE (90 °C) fixed singlecore cable (flat), 120 mm² earth, 50 m; unenclosed, spaced from surface & trefoil or flat touching, on ladder, racks or cleats, 1 circuit(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 36.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 630 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 600.0 A (specified)
Check 1 — capacity	Base rating Table 8, column 2, row 400: 899 A. Derating Table 23, 18 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 899 × 1.00 = 899.0 A vs I_design 600.0 A (loading 66.7 %) PASS
Check 2 — voltage drop	R_c = 0.0646 Ω/km (Table 34), X_c = 0.0955 Ω/km (Table 30). At the design current, ΔV = √3 × 600.0 × 0.050 × (0.0646 × 0.85 + 0.0955 × 0.527) = 5.47 V (drop) = 1.32 % of 415 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 400)² / 36,000² = 2.525 s vs 0.1 s; S_min = 36,000 × √0.1 / 143 = 79.6 mm² PASS
Check 4 — earth fault loop	Earth 120 mm²: R_e = 0.197, X_e = 0.0996 Ω/km (Table 30 at the earth size), Z_earth = 0.050 × √(0.197² + 0.0996²) = 0.0110 Ω. Z_loop = 0.03 + 0.0058 (phase) + 0.0110 (earth) = 0.0468 Ω. I_fault = 415/√3 / 0.0468 = 5,119 A vs 630 × 5 = 3,150 A; L_max = 137 m vs 50 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 600.0 A ≤ 630 A ≤ 899.0 A (device at 70.1 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 400 mm² phase conductor: 120 mm²; earth 120 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 415/√3 / 0.03 = 7,987 A. S_e,min = 7,987 × √0.04 (t_ef) / 143 = 11.17 mm² (k as the phase conductor, Table 52) vs 120 mm²; t_max = 4.616 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 3,488 W (0.95 %)

Example 15 — 185 mm² shaped-conductor multicore cable

Shaped conductors take their resistance from Table 36 and reactance from the shaped column of Table 30.

Given: 180 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 185 mm² copper XLPE (90 °C) fixed multicore cable (shaped conductors), 70 mm² earth, 95 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 25.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 400 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 180.00 kW × 1000 / (√3 × 400 × 0.85) = 305.7 A
Check 1 — capacity	Base rating Table 14, column 2, row 185: 428 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 428 × 1.00 = 428.0 A vs I_design 305.7 A (loading 71.4 %) PASS
Check 2 — voltage drop	R_c = 0.128 Ω/km (Table 36), X_c = 0.0663 Ω/km (Table 30). At the design current, ΔV = √3 × 305.7 × 0.095 × (0.128 × 0.85 + 0.0663 × 0.527) = 7.23 V (drop) = 1.81 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 185)² / 25,000² = 1.120 s vs 0.1 s; S_min = 25,000 × √0.1 / 143 = 55.3 mm² PASS
Check 4 — earth fault loop	Earth 70 mm²: R_e = 0.342, X_e = 0.0683 Ω/km (Table 30 at the earth size), Z_earth = 0.095 × √(0.342² + 0.0683²) = 0.0331 Ω. Z_loop = 0.03 + 0.0137 (phase) + 0.0331 (earth) = 0.0768 Ω. I_fault = 400/√3 / 0.0768 = 3,006 A vs 400 × 5 = 2,000 A; L_max = 173 m vs 95 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 305.7 A ≤ 400 A ≤ 428.0 A (device at 93.5 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 185 mm² phase conductor: 70 mm²; earth 70 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 70 mm²; t_max = 1.691 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 3,408 W (1.89 %)

Example 16 — Two circuits bunched on a wall surface

Multicore touching a surface: Table 22 grouping for two bunched circuits.

Given: 55 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 50 mm² copper XLPE (90 °C) fixed multicore cable, 16 mm² earth, 70 m; unenclosed, touching a surface, 2 circuit(s) bunched on a surface, air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 125 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 55.00 kW × 1000 / (√3 × 400 × 0.85) = 93.4 A
Check 1 — capacity	Base rating Table 14, column 5, row 50: 168 A. Derating Table 22, column 3, row 2: 0.800; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 0.800. I_derated = 168 × 0.800 = 134.4 A vs I_design 93.4 A (loading 69.5 %) PASS
Check 2 — voltage drop	R_c = 0.494 Ω/km (Table 35), X_c = 0.0751 Ω/km (Table 30). At the design current, ΔV = √3 × 93.4 × 0.070 × (0.494 × 0.85 + 0.0751 × 0.527) = 5.20 V (drop) = 1.30 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 50)² / 10,000² = 0.511 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 16 mm²: R_e = 1.47, X_e = 0.0805 Ω/km (Table 30 at the earth size), Z_earth = 0.070 × √(1.47² + 0.0805²) = 0.1031 Ω. Z_loop = 0.03 + 0.0350 (phase) + 0.1031 (earth) = 0.1680 Ω. I_fault = 400/√3 / 0.1680 = 1,374 A vs 125 × 5 = 625 A; L_max = 172 m vs 70 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 93.4 A ≤ 125 A ≤ 134.4 A (device at 93.0 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 50 mm² phase conductor: 16 mm²; earth 16 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 16 mm²; t_max = 0.088 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 905 W (1.65 %)

Example 17 — Six cables per tier on two tiers of perforated tray

Table 24 grouping for multicore cables touching on stacked perforated trays.

Given: 75 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 95 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 85 m; unenclosed, spaced from surface, on perforated trays horizontal, 6 cable(s) per tier, 2 tier(s), touching, air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 160 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 75.00 kW × 1000 / (√3 × 400 × 0.85) = 127.4 A
Check 1 — capacity	Base rating Table 14, column 2, row 95: 275 A. Derating Table 24, 8 °C conductor column, row 6: 0.730; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 0.730. I_derated = 275 × 0.730 = 200.8 A vs I_design 127.4 A (loading 63.4 %) PASS
Check 2 — voltage drop	R_c = 0.248 Ω/km (Table 35), X_c = 0.0725 Ω/km (Table 30). At the design current, ΔV = √3 × 127.4 × 0.085 × (0.248 × 0.85 + 0.0725 × 0.527) = 4.67 V (drop) = 1.17 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 95)² / 10,000² = 1.846 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.085 × √(0.927² + 0.0808²) = 0.0791 Ω. Z_loop = 0.03 + 0.0220 (phase) + 0.0791 (earth) = 0.1311 Ω. I_fault = 400/√3 / 0.1311 = 1,762 A vs 160 × 5 = 800 A; L_max = 218 m vs 85 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 127.4 A ≤ 160 A ≤ 200.8 A (device at 79.7 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 95 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 1,026 W (1.37 %)

Example 18 — Three cables touching on a single ladder rack

Table 24 grouping for touching multicore cables on a ladder.

Given: 65 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 70 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 60 m; unenclosed, spaced from surface, on ladder, racks or cleats, 3 cable(s) per tier, 1 tier(s), touching, air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 125 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 65.00 kW × 1000 / (√3 × 400 × 0.85) = 110.4 A
Check 1 — capacity	Base rating Table 14, column 2, row 70: 230 A. Derating Table 24, 13 °C conductor column, row 3: 0.820; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 0.820. I_derated = 230 × 0.820 = 188.6 A vs I_design 110.4 A (loading 58.5 %) PASS
Check 2 — voltage drop	R_c = 0.343 Ω/km (Table 35), X_c = 0.0741 Ω/km (Table 30). At the design current, ΔV = √3 × 110.4 × 0.060 × (0.343 × 0.85 + 0.0741 × 0.527) = 3.79 V (drop) = 0.95 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 70)² / 10,000² = 1.002 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.060 × √(0.927² + 0.0808²) = 0.0558 Ω. Z_loop = 0.03 + 0.0211 (phase) + 0.0558 (earth) = 0.1069 Ω. I_fault = 400/√3 / 0.1069 = 2,161 A vs 125 × 5 = 625 A; L_max = 265 m vs 60 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 110.4 A ≤ 125 A ≤ 188.6 A (device at 66.3 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 70 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 752 W (1.16 %)

Example 19 — Three circuits bunched on a catenary wire

Cables bunched on a catenary are grouped with Table 22 rather than Table 24. The 10 mm² Table 5.1 earth fails its withstand: 7.7 kA from the 0.03 Ω source needs 10.8 mm² even for 0.04 s.

Given: 40 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 35 mm² copper XLPE (90 °C) fixed multicore cable, 10 mm² earth, 55 m; unenclosed, bunched on catinerary wire, 3 circuit(s), air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 80 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 40.00 kW × 1000 / (√3 × 400 × 0.85) = 67.9 A
Check 1 — capacity	Base rating Table 14, column 2, row 35: 144 A. Derating Table 22, column 2, row 3: 0.750; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 0.750. I_derated = 144 × 0.750 = 108.0 A vs I_design 67.9 A (loading 62.9 %) PASS
Check 2 — voltage drop	R_c = 0.669 Ω/km (Table 35), X_c = 0.0786 Ω/km (Table 30). At the design current, ΔV = √3 × 67.9 × 0.055 × (0.669 × 0.85 + 0.0786 × 0.527) = 3.95 V (drop) = 0.99 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 35)² / 10,000² = 0.251 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 10 mm²: R_e = 2.33, X_e = 0.0840 Ω/km (Table 30 at the earth size), Z_earth = 0.055 × √(2.33² + 0.0840²) = 0.1282 Ω. Z_loop = 0.03 + 0.0370 (phase) + 0.1282 (earth) = 0.1953 Ω. I_fault = 400/√3 / 0.1953 = 1,183 A vs 80 × 5 = 400 A; L_max = 182 m vs 55 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 67.9 A ≤ 80 A ≤ 108.0 A (device at 74.1 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 35 mm² phase conductor: 10 mm²; earth 10 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 10 mm²; t_max = 0.035 s FAIL
Result	6/7 checks pass → FAIL; governing criterion Earth Withstand; power loss 509 W (1.27 %). Earth conductor 10 mm² < 10.8 mm² needed for 7698 A in 0.04 s

Example 20 — Two single-core trefoil circuits on a ladder

Single-core cables on a ladder use Table 23 for grouping. The circuits are trefoil groups: spaced conductors would be rejected, as Table 30 gives single-core reactance only for trefoil and flat touching.

Given: 150 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 120 mm² copper XLPE (90 °C) fixed singlecore cable (trefoil), 35 mm² earth, 75 m; unenclosed, spaced from surface & trefoil or flat touching, on ladder, racks or cleats, 2 circuit(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 20.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 315 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 150.00 kW × 1000 / (√3 × 400 × 0.85) = 254.7 A
Check 1 — capacity	Base rating Table 8, column 2, row 120: 410 A. Derating Table 23, 18 °C conductor column, row 2: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 410 × 1.00 = 410.0 A vs I_design 254.7 A (loading 62.1 %) PASS
Check 2 — voltage drop	R_c = 0.197 Ω/km (Table 34), X_c = 0.0844 Ω/km (Table 30). At the design current, ΔV = √3 × 254.7 × 0.075 × (0.197 × 0.85 + 0.0844 × 0.527) = 7.01 V (drop) = 1.75 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 120)² / 20,000² = 0.736 s vs 0.1 s; S_min = 20,000 × √0.1 / 143 = 44.2 mm² PASS
Check 4 — earth fault loop	Earth 35 mm²: R_e = 0.668, X_e = 0.0982 Ω/km (Table 30 at the earth size), Z_earth = 0.075 × √(0.668² + 0.0982²) = 0.0506 Ω. Z_loop = 0.03 + 0.0161 (phase) + 0.0506 (earth) = 0.0967 Ω. I_fault = 400/√3 / 0.0967 = 2,388 A vs 315 × 5 = 1,575 A; L_max = 131 m vs 75 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 254.7 A ≤ 315 A ≤ 410.0 A (device at 76.8 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 120 mm² phase conductor: 35 mm²; earth 35 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 35 mm²; t_max = 0.423 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 2,876 W (1.92 %)

Example 21 — Four circuits in a wiring enclosure in air

Enclosed multicore cables: Table 22 grouping for four circuits brings the cable under the 100 A device, so overload coordination fails although the load itself is carried.

Given: 45 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 50 mm² copper XLPE (90 °C) fixed multicore cable, 16 mm² earth, 65 m; enclosed in a wiring enclosure in air, 4 circuit(s), air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 100 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 45.00 kW × 1000 / (√3 × 400 × 0.85) = 76.4 A
Check 1 — capacity	Base rating Table 14, column 11, row 50: 136 A. Derating Table 22, column 2, row 4: 0.720; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 0.720. I_derated = 136 × 0.720 = 97.9 A vs I_design 76.4 A (loading 78.0 %) PASS
Check 2 — voltage drop	R_c = 0.494 Ω/km (Table 35), X_c = 0.0751 Ω/km (Table 30). At the design current, ΔV = √3 × 76.4 × 0.065 × (0.494 × 0.85 + 0.0751 × 0.527) = 3.95 V (drop) = 0.99 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 50)² / 10,000² = 0.511 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 16 mm²: R_e = 1.47, X_e = 0.0805 Ω/km (Table 30 at the earth size), Z_earth = 0.065 × √(1.47² + 0.0805²) = 0.0957 Ω. Z_loop = 0.03 + 0.0325 (phase) + 0.0957 (earth) = 0.1582 Ω. I_fault = 400/√3 / 0.1582 = 1,460 A vs 100 × 5 = 500 A; L_max = 219 m vs 65 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 76.4 A ≤ 100 A ≤ 97.9 A (device at 102.1 % of cable capacity) FAIL
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 50 mm² phase conductor: 16 mm²; earth 16 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 16 mm²; t_max = 0.088 s PASS
Result	6/7 checks pass → FAIL; governing criterion Overload; power loss 562 W (1.25 %). Device rating (100A) > Derated capacity (97.9A)

Example 22 — Single-core cables in a metallic enclosure

Single-core cables enclosed in a metal duct with two circuits: Table 22 grouping overloads the 95 mm² cable.

Given: 120 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 95 mm² copper XLPE (90 °C) fixed singlecore cable (trefoil), 25 mm² earth, 70 m; enclosed in a metallic enclosure, 2 circuit(s), air ambient 40 °C. Protection: prospective fault 20.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 250 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 120.00 kW × 1000 / (√3 × 400 × 0.85) = 203.8 A
Check 1 — capacity	Base rating Table 8, column 17, row 95: 171 A. Derating Table 22, column 2, row 2: 0.870; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 0.870. I_derated = 171 × 0.870 = 148.8 A vs I_design 203.8 A (loading 137.0 %) FAIL
Check 2 — voltage drop	R_c = 0.247 Ω/km (Table 34), X_c = 0.0868 Ω/km (Table 30). At the design current, ΔV = √3 × 203.8 × 0.070 × (0.247 × 0.85 + 0.0868 × 0.527) = 6.32 V (drop) = 1.58 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 95)² / 20,000² = 0.461 s vs 0.1 s; S_min = 20,000 × √0.1 / 143 = 44.2 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.102 Ω/km (Table 30 at the earth size), Z_earth = 0.070 × √(0.927² + 0.102²) = 0.0653 Ω. Z_loop = 0.03 + 0.0183 (phase) + 0.0653 (earth) = 0.1136 Ω. I_fault = 400/√3 / 0.1136 = 2,033 A vs 250 × 5 = 1,250 A; L_max = 130 m vs 70 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 203.8 A ≤ 250 A ≤ 148.8 A (device at 168.0 % of cable capacity) FAIL
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 95 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	5/7 checks pass → FAIL; governing criterion Overload; power loss 2,154 W (1.79 %). Derated capacity (148.8A) < Design current (203.8A); Device rating (250A) > Derated capacity (148.8A)

Example 23 — Three circuits in a conduit in air

Conduit in air is treated as a bunched group: Table 22, three circuits. The 6 mm² earth fails its withstand against the 7.7 kA near-end earth fault.

Given: 30 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 25 mm² copper XLPE (90 °C) fixed multicore cable, 6 mm² earth, 50 m; in conduit in air, 3 circuit(s), air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 63 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 30.00 kW × 1000 / (√3 × 400 × 0.85) = 50.9 A
Check 1 — capacity	Base rating Table 14, column 25, row 25: 107 A. Derating Table 22, column 2, row 3: 0.750; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 0.750. I_derated = 107 × 0.750 = 80.2 A vs I_design 50.9 A (loading 63.5 %) PASS
Check 2 — voltage drop	R_c = 0.927 Ω/km (Table 35), X_c = 0.0808 Ω/km (Table 30). At the design current, ΔV = √3 × 50.9 × 0.050 × (0.927 × 0.85 + 0.0808 × 0.527) = 3.66 V (drop) = 0.92 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 25)² / 10,000² = 0.128 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 6 mm²: R_e = 3.93, X_e = 0.0887 Ω/km (Table 30 at the earth size), Z_earth = 0.050 × √(3.93² + 0.0887²) = 0.1966 Ω. Z_loop = 0.03 + 0.0465 (phase) + 0.1966 (earth) = 0.2731 Ω. I_fault = 400/√3 / 0.2731 = 846 A vs 63 × 5 = 315 A; L_max = 145 m vs 50 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 50.9 A ≤ 63 A ≤ 80.2 A (device at 78.5 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 25 mm² phase conductor: 6 mm²; earth 6 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 6 mm²; t_max = 0.012 s FAIL
Result	6/7 checks pass → FAIL; governing criterion Earth Withstand; power loss 361 W (1.20 %). Earth conductor 6 mm² < 10.8 mm² needed for 7698 A in 0.04 s

Example 24 — Three multicore cables direct buried, touching

Direct buried: grouping (25(2)), soil temperature (27(2)), depth (28(1)) and soil resistivity (29).

Given: 80 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 95 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 160 m; direct buried, 3 cable(s)/circuit(s) touching, depth 0.8 m, soil 1.2 K·m/W at 25 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 160 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 80.00 kW × 1000 / (√3 × 400 × 0.85) = 135.8 A
Check 1 — capacity	Base rating Table 14, column 23, row 95: 302 A. Derating Table 25(2), column 2, row 3: 0.700; Table 27(2), 90 °C conductor column, row 25: 1.00; Table 28(1), column 3, row 0.8: 0.960; Table 29, column 2, row 1.2: 1.00 → F = 0.672. I_derated = 302 × 0.672 = 202.9 A vs I_design 135.8 A (loading 66.9 %) PASS
Check 2 — voltage drop	R_c = 0.248 Ω/km (Table 35), X_c = 0.0725 Ω/km (Table 30). At the design current, ΔV = √3 × 135.8 × 0.160 × (0.248 × 0.85 + 0.0725 × 0.527) = 9.37 V (drop) = 2.34 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 95)² / 10,000² = 1.846 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.160 × √(0.927² + 0.0808²) = 0.1489 Ω. Z_loop = 0.03 + 0.0413 (phase) + 0.1489 (earth) = 0.2202 Ω. I_fault = 400/√3 / 0.2202 = 1,049 A vs 160 × 5 = 800 A; L_max = 218 m vs 160 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 135.8 A ≤ 160 A ≤ 202.9 A (device at 78.8 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 95 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 2,197 W (2.75 %)

Example 25 — Single-core trefoil direct buried at 1.0 m in 1.5 K·m/W soil

Single-core direct buried uses Table 25(1); deeper burial and poorer soil both derate.

Given: 220 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 240 mm² copper XLPE (90 °C) fixed singlecore cable (trefoil), 95 mm² earth, 130 m; direct buried, 1 cable(s)/circuit(s) touching, depth 1 m, soil 1.5 K·m/W at 25 °C. Protection: prospective fault 20.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 400 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 220.00 kW × 1000 / (√3 × 400 × 0.85) = 373.6 A
Check 1 — capacity	Base rating Table 8, column 22, row 240: 523 A. Derating Table 27(2), 90 °C conductor column, row 25: 1.00; Table 28(1), column 3, row 1: 0.940; Table 29, column 3, row 1.5: 0.900 → F = 0.846. I_derated = 523 × 0.846 = 442.5 A vs I_design 373.6 A (loading 84.4 %) PASS
Check 2 — voltage drop	R_c = 0.0991 Ω/km (Table 34), X_c = 0.0818 Ω/km (Table 30). At the design current, ΔV = √3 × 373.6 × 0.130 × (0.0991 × 0.85 + 0.0818 × 0.527) = 10.71 V (drop) = 2.68 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 240)² / 20,000² = 2.945 s vs 0.1 s; S_min = 20,000 × √0.1 / 143 = 44.2 mm² PASS
Check 4 — earth fault loop	Earth 95 mm²: R_e = 0.247, X_e = 0.0868 Ω/km (Table 30 at the earth size), Z_earth = 0.130 × √(0.247² + 0.0868²) = 0.0340 Ω. Z_loop = 0.03 + 0.0167 (phase) + 0.0340 (earth) = 0.0807 Ω. I_fault = 400/√3 / 0.0807 = 2,860 A vs 400 × 5 = 2,000 A; L_max = 219 m vs 130 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 373.6 A ≤ 400 A ≤ 442.5 A (device at 90.4 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 240 mm² phase conductor: 95 mm²; earth 95 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 95 mm²; t_max = 3.114 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 5,394 W (2.45 %)

Example 26 — Two multicore cables in separate buried conduits 0.3 m apart

Buried conduit: Table 26(2) grouping, 27(2) soil temperature, 28(2) depth and 29 soil resistivity.

Given: 70 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 95 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 150 m; in buried conduit, 2 conduit(s) spaced 0.3 m, depth 0.6 m, soil 1 K·m/W at 25 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 160 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 70.00 kW × 1000 / (√3 × 400 × 0.85) = 118.9 A
Check 1 — capacity	Base rating Table 14, column 25, row 95: 233 A. Derating Table 26(2), column 3, row 2: 0.950; Table 27(2), 90 °C conductor column, row 25: 1.00; Table 28(2), column 3, row 0.6: 0.990; Table 29, column 4, row 1: 1.03 → F = 0.969. I_derated = 233 × 0.969 = 225.7 A vs I_design 118.9 A (loading 52.7 %) PASS
Check 2 — voltage drop	R_c = 0.248 Ω/km (Table 35), X_c = 0.0725 Ω/km (Table 30). At the design current, ΔV = √3 × 118.9 × 0.150 × (0.248 × 0.85 + 0.0725 × 0.527) = 7.69 V (drop) = 1.92 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 95)² / 10,000² = 1.846 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.150 × √(0.927² + 0.0808²) = 0.1396 Ω. Z_loop = 0.03 + 0.0388 (phase) + 0.1396 (earth) = 0.2083 Ω. I_fault = 400/√3 / 0.2083 = 1,109 A vs 160 × 5 = 800 A; L_max = 218 m vs 150 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 118.9 A ≤ 160 A ≤ 225.7 A (device at 70.9 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 95 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 1,577 W (2.25 %)

Example 27 — Single-core circuit in a shared buried conduit

All three phases in one buried conduit: the shared-conduit rating column and Table 26(1) grouping. One conduit per phase (dedicated) would be rejected, as Table 30 gives no reactance for that spacing.

Given: 180 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 240 mm² copper XLPE (90 °C) fixed singlecore cable (trefoil), 95 mm² earth, 120 m; in shared buried conduit, 1 conduit(s) touching, depth 0.8 m, soil 1 K·m/W at 25 °C. Protection: prospective fault 20.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 315 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 180.00 kW × 1000 / (√3 × 400 × 0.85) = 305.7 A
Check 1 — capacity	Base rating Table 8, column 24, row 240: 426 A. Derating Table 27(2), 90 °C conductor column, row 25: 1.00; Table 28(2), column 2, row 0.8: 0.950; Table 29, column 6, row 1: 1.04 → F = 0.988. I_derated = 426 × 0.988 = 420.9 A vs I_design 305.7 A (loading 72.6 %) PASS
Check 2 — voltage drop	R_c = 0.0991 Ω/km (Table 34), X_c = 0.0818 Ω/km (Table 30). At the design current, ΔV = √3 × 305.7 × 0.120 × (0.0991 × 0.85 + 0.0818 × 0.527) = 8.09 V (drop) = 2.02 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 240)² / 20,000² = 2.945 s vs 0.1 s; S_min = 20,000 × √0.1 / 143 = 44.2 mm² PASS
Check 4 — earth fault loop	Earth 95 mm²: R_e = 0.247, X_e = 0.0868 Ω/km (Table 30 at the earth size), Z_earth = 0.120 × √(0.247² + 0.0868²) = 0.0314 Ω. Z_loop = 0.03 + 0.0154 (phase) + 0.0314 (earth) = 0.0768 Ω. I_fault = 400/√3 / 0.0768 = 3,006 A vs 315 × 5 = 1,575 A; L_max = 299 m vs 120 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 305.7 A ≤ 315 A ≤ 420.9 A (device at 74.8 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 240 mm² phase conductor: 95 mm²; earth 95 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 95 mm²; t_max = 3.114 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 3,333 W (1.85 %)

Example 28 — Cable completely surrounded by thermal insulation, enclosed

The most onerous thermal-insulation column: even 16 mm² falls short for 25 kW and its 50 A device, and its 6 mm² earth fails its withstand (compare Example 12).

Given: 25 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 16 mm² copper XLPE (90 °C) fixed multicore cable, 6 mm² earth, 35 m; completely surrounded by thermal insulation, enclosed, air ambient 40 °C. Protection: prospective fault 6.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 50 A device with 5× instantaneous trip, source impedance 0.04 Ω, voltage-drop limit 5 %.

Load current	I_load = 25.00 kW × 1000 / (√3 × 400 × 0.85) = 42.5 A
Check 1 — capacity	Base rating Table 14, column 21, row 16: 34 A. Derating Table 22, column 2, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 34 × 1.00 = 34.0 A vs I_design 42.5 A (loading 124.9 %) FAIL
Check 2 — voltage drop	R_c = 1.47 Ω/km (Table 35), X_c = 0.0805 Ω/km (Table 30). At the design current, ΔV = √3 × 42.5 × 0.035 × (1.47 × 0.85 + 0.0805 × 0.527) = 3.32 V (drop) = 0.83 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 16)² / 6,000² = 0.145 s vs 0.1 s; S_min = 6,000 × √0.1 / 143 = 13.3 mm² PASS
Check 4 — earth fault loop	Earth 6 mm²: R_e = 3.93, X_e = 0.0887 Ω/km (Table 30 at the earth size), Z_earth = 0.035 × √(3.93² + 0.0887²) = 0.1376 Ω. Z_loop = 0.04 + 0.0515 (phase) + 0.1376 (earth) = 0.2291 Ω. I_fault = 400/√3 / 0.2291 = 1,008 A vs 50 × 5 = 250 A; L_max = 164 m vs 35 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 42.5 A ≤ 50 A ≤ 34.0 A (device at 147.1 % of cable capacity) FAIL
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 16 mm² phase conductor: 6 mm²; earth 6 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.04 = 5,774 A. S_e,min = 5,774 × √0.04 (t_ef) / 143 = 8.07 mm² (k as the phase conductor, Table 52) vs 6 mm²; t_max = 0.022 s FAIL
Result	4/7 checks pass → FAIL; governing criterion Overload; power loss 278 W (1.11 %). Derated capacity (34.0A) < Design current (42.5A); Device rating (50A) > Derated capacity (34.0A); Earth conductor 6 mm² < 8.1 mm² needed for 5774 A in 0.04 s

Example 29 — 55 °C switchroom ambient

Table 27(1) at 55 °C takes 19 % off a 90 °C cable rating, and the 200 A device then exceeds the derated capacity.

Given: 95 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 70 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 60 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 55 °C. Protection: prospective fault 15.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 200 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 95.00 kW × 1000 / (√3 × 400 × 0.85) = 161.3 A
Check 1 — capacity	Base rating Table 14, column 2, row 70: 230 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 55: 0.810 → F = 0.810. I_derated = 230 × 0.810 = 186.3 A vs I_design 161.3 A (loading 86.6 %) PASS
Check 2 — voltage drop	R_c = 0.343 Ω/km (Table 35), X_c = 0.0741 Ω/km (Table 30). At the design current, ΔV = √3 × 161.3 × 0.060 × (0.343 × 0.85 + 0.0741 × 0.527) = 5.54 V (drop) = 1.39 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 70)² / 15,000² = 0.445 s vs 0.1 s; S_min = 15,000 × √0.1 / 143 = 33.2 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.060 × √(0.927² + 0.0808²) = 0.0558 Ω. Z_loop = 0.03 + 0.0211 (phase) + 0.0558 (earth) = 0.1069 Ω. I_fault = 400/√3 / 0.1069 = 2,161 A vs 200 × 5 = 1,000 A; L_max = 157 m vs 60 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 161.3 A ≤ 200 A ≤ 186.3 A (device at 107.4 % of cable capacity) FAIL
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 70 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	6/7 checks pass → FAIL; governing criterion Overload; power loss 1,607 W (1.69 %). Device rating (200A) > Derated capacity (186.3A)

Example 30 — 25 °C ambient with a PVC cable

Below 40 °C the rating is uplifted (Table 27(1), 75 °C conductors at 25 °C); the fault withstand still fails by a small margin, and the 6 mm² earth with the lower PVC k fails its withstand.

Given: 20 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 16 mm² copper PVC (75 °C) fixed multicore cable, 6 mm² earth, 40 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 25 °C. Protection: prospective fault 6.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 40 A device with 5× instantaneous trip, source impedance 0.04 Ω, voltage-drop limit 5 %.

Load current	I_load = 20.00 kW × 1000 / (√3 × 400 × 0.85) = 34.0 A
Check 1 — capacity	Base rating Table 13, column 2, row 16: 72 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 75 °C conductor column, row 25: 1.21 → F = 1.21. I_derated = 72 × 1.21 = 87.1 A vs I_design 34.0 A (loading 39.0 %) PASS
Check 2 — voltage drop	R_c = 1.40 Ω/km (Table 35), X_c = 0.0861 Ω/km (Table 30). At the design current, ΔV = √3 × 34.0 × 0.040 × (1.40 × 0.85 + 0.0861 × 0.527) = 2.91 V (drop) = 0.73 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 111 (Table 52). t_max = (111 × 16)² / 6,000² = 0.088 s vs 0.1 s; S_min = 6,000 × √0.1 / 111 = 17.1 mm² FAIL
Check 4 — earth fault loop	Earth 6 mm²: R_e = 3.75, X_e = 0.0967 Ω/km (Table 30 at the earth size), Z_earth = 0.040 × √(3.75² + 0.0967²) = 0.1500 Ω. Z_loop = 0.04 + 0.0561 (phase) + 0.1500 (earth) = 0.2462 Ω. I_fault = 400/√3 / 0.2462 = 938 A vs 40 × 5 = 200 A; L_max = 216 m vs 40 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 34.0 A ≤ 40 A ≤ 87.1 A (device at 45.9 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 16 mm² phase conductor: 6 mm²; earth 6 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.04 = 5,774 A. S_e,min = 5,774 × √0.04 (t_ef) / 111 = 10.40 mm² (k as the phase conductor, Table 52) vs 6 mm²; t_max = 0.013 s FAIL
Result	5/7 checks pass → FAIL; governing criterion Earth Withstand; power loss 194 W (0.97 %). Insufficient withstand: 0.088s < 0.1s; Earth conductor 6 mm² < 10.4 mm² needed for 5774 A in 0.04 s

Example 31 — Hot, dry soil: 35 °C at 1.5 m depth in 2.5 K·m/W ground

Underground derating stacks up: soil temperature, depth and resistivity together remove over half the rating.

Given: 60 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 95 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 200 m; direct buried, 1 cable(s)/circuit(s) touching, depth 1.5 m, soil 2.5 K·m/W at 35 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 125 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 60.00 kW × 1000 / (√3 × 400 × 0.85) = 101.9 A
Check 1 — capacity	Base rating Table 14, column 23, row 95: 302 A. Derating Table 27(2), 90 °C conductor column, row 35: 0.930; Table 28(1), column 3, row 1.5: 0.910; Table 29, column 2, row 2.5: 0.740 → F = 0.626. I_derated = 302 × 0.626 = 189.1 A vs I_design 101.9 A (loading 53.9 %) PASS
Check 2 — voltage drop	R_c = 0.248 Ω/km (Table 35), X_c = 0.0725 Ω/km (Table 30). At the design current, ΔV = √3 × 101.9 × 0.200 × (0.248 × 0.85 + 0.0725 × 0.527) = 8.79 V (drop) = 2.20 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 95)² / 10,000² = 1.846 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.200 × √(0.927² + 0.0808²) = 0.1861 Ω. Z_loop = 0.03 + 0.0517 (phase) + 0.1861 (earth) = 0.2678 Ω. I_fault = 400/√3 / 0.2678 = 862 A vs 125 × 5 = 625 A; L_max = 286 m vs 200 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 101.9 A ≤ 125 A ≤ 189.1 A (device at 66.1 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 95 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 1,545 W (2.57 %)

Example 32 — 36 kA fault level with a 0.3 s clearing time

Short-circuit withstand governs: 95 mm² cannot survive 36 kA for 0.3 s.

Given: 90 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 95 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 80 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 36.0 kA cleared in 0.3 s, earth-fault clearing time 0.04 s, 200 A device with 5× instantaneous trip, source impedance 0.02 Ω, voltage-drop limit 5 %.

Load current	I_load = 90.00 kW × 1000 / (√3 × 400 × 0.85) = 152.8 A
Check 1 — capacity	Base rating Table 14, column 2, row 95: 275 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 275 × 1.00 = 275.0 A vs I_design 152.8 A (loading 55.6 %) PASS
Check 2 — voltage drop	R_c = 0.248 Ω/km (Table 35), X_c = 0.0725 Ω/km (Table 30). At the design current, ΔV = √3 × 152.8 × 0.080 × (0.248 × 0.85 + 0.0725 × 0.527) = 5.27 V (drop) = 1.32 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 95)² / 36,000² = 0.142 s vs 0.3 s; S_min = 36,000 × √0.3 / 143 = 137.9 mm² FAIL
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.080 × √(0.927² + 0.0808²) = 0.0744 Ω. Z_loop = 0.02 + 0.0207 (phase) + 0.0744 (earth) = 0.1151 Ω. I_fault = 400/√3 / 0.1151 = 2,006 A vs 200 × 5 = 1,000 A; L_max = 177 m vs 80 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 152.8 A ≤ 200 A ≤ 275.0 A (device at 72.7 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 95 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.02 = 11,547 A. S_e,min = 11,547 × √0.04 (t_ef) / 143 = 16.15 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.096 s PASS
Result	6/7 checks pass → FAIL; governing criterion Short Circuit; power loss 1,390 W (1.54 %). Insufficient withstand: 0.142s < 0.3s

Example 33 — 350 m run on a 160 A type-D breaker

Earth-fault loop impedance fails: the loop is too long to drive 10 × 160 A.

Given: 75 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 70 mm² copper XLPE (90 °C) fixed multicore cable, 25 mm² earth, 350 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 160 A device with 10× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 75.00 kW × 1000 / (√3 × 400 × 0.85) = 127.4 A
Check 1 — capacity	Base rating Table 14, column 2, row 70: 230 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 230 × 1.00 = 230.0 A vs I_design 127.4 A (loading 55.4 %) PASS
Check 2 — voltage drop	R_c = 0.343 Ω/km (Table 35), X_c = 0.0741 Ω/km (Table 30). At the design current, ΔV = √3 × 127.4 × 0.350 × (0.343 × 0.85 + 0.0741 × 0.527) = 25.52 V (drop) = 6.38 % of 400 V, limit 5 % FAIL
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 70)² / 10,000² = 1.002 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 25 mm²: R_e = 0.927, X_e = 0.0808 Ω/km (Table 30 at the earth size), Z_earth = 0.350 × √(0.927² + 0.0808²) = 0.3257 Ω. Z_loop = 0.03 + 0.1228 (phase) + 0.3257 (earth) = 0.4785 Ω. I_fault = 400/√3 / 0.4785 = 483 A vs 160 × 10 = 1,600 A; L_max = 89 m vs 350 m FAIL
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 127.4 A ≤ 160 A ≤ 230.0 A (device at 69.6 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 70 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 25 mm²; t_max = 0.216 s PASS
Result	5/7 checks pass → FAIL; governing criterion Earth Fault; power loss 5,842 W (7.79 %). Voltage drop (6.38%) > Maximum allowed (5%); Insufficient fault current: 482.6A < 1600.0A; Cable too long: 350.0m > 89.2m

Example 34 — Full-size earth conductor on a long 95 mm² feeder

Compare with Example 1: a 95 mm² earth lowers the loop impedance and lengthens the permitted run.

Given: 90 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 95 mm² copper XLPE (90 °C) fixed multicore cable, 95 mm² earth, 180 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 200 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 90.00 kW × 1000 / (√3 × 400 × 0.85) = 152.8 A
Check 1 — capacity	Base rating Table 14, column 2, row 95: 275 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 275 × 1.00 = 275.0 A vs I_design 152.8 A (loading 55.6 %) PASS
Check 2 — voltage drop	R_c = 0.248 Ω/km (Table 35), X_c = 0.0725 Ω/km (Table 30). At the design current, ΔV = √3 × 152.8 × 0.180 × (0.248 × 0.85 + 0.0725 × 0.527) = 11.86 V (drop) = 2.97 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 95)² / 10,000² = 1.846 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 95 mm²: R_e = 0.248, X_e = 0.0725 Ω/km (Table 30 at the earth size), Z_earth = 0.180 × √(0.248² + 0.0725²) = 0.0465 Ω. Z_loop = 0.03 + 0.0465 (phase) + 0.0465 (earth) = 0.1230 Ω. I_fault = 400/√3 / 0.1230 = 1,877 A vs 200 × 5 = 1,000 A; L_max = 389 m vs 180 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 152.8 A ≤ 200 A ≤ 275.0 A (device at 72.7 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 95 mm² phase conductor: 25 mm²; earth 95 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 95 mm²; t_max = 3.114 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 3,128 W (3.48 %)

Example 35 — Stiff supply: 0.02 Ω source and 25 kA cleared in 50 ms

A low source impedance and a fast breaker: high loop current and a short adiabatic requirement.

Given: 120 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. 120 mm² copper XLPE (90 °C) fixed multicore cable, 35 mm² earth, 60 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 25.0 kA cleared in 0.05 s, earth-fault clearing time 0.04 s, 250 A device with 5× instantaneous trip, source impedance 0.02 Ω, voltage-drop limit 5 %.

Load current	I_load = 120.00 kW × 1000 / (√3 × 400 × 0.85) = 203.8 A
Check 1 — capacity	Base rating Table 14, column 2, row 120: 327 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 327 × 1.00 = 327.0 A vs I_design 203.8 A (loading 62.3 %) PASS
Check 2 — voltage drop	R_c = 0.197 Ω/km (Table 35), X_c = 0.0713 Ω/km (Table 30). At the design current, ΔV = √3 × 203.8 × 0.060 × (0.197 × 0.85 + 0.0713 × 0.527) = 4.34 V (drop) = 1.09 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 120)² / 25,000² = 0.471 s vs 0.05 s; S_min = 25,000 × √0.05 / 143 = 39.1 mm² PASS
Check 4 — earth fault loop	Earth 35 mm²: R_e = 0.669, X_e = 0.0786 Ω/km (Table 30 at the earth size), Z_earth = 0.060 × √(0.669² + 0.0786²) = 0.0404 Ω. Z_loop = 0.02 + 0.0126 (phase) + 0.0404 (earth) = 0.0730 Ω. I_fault = 400/√3 / 0.0730 = 3,164 A vs 250 × 5 = 1,250 A; L_max = 187 m vs 60 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 203.8 A ≤ 250 A ≤ 327.0 A (device at 76.5 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 120 mm² phase conductor: 35 mm²; earth 35 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.02 = 11,547 A. S_e,min = 11,547 × √0.04 (t_ef) / 143 = 16.15 mm² (k as the phase conductor, Table 52) vs 35 mm²; t_max = 0.188 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 1,472 W (1.23 %)

Example 36 — 300 ft run entered in feet at 415 V

Lengths in feet are converted to metres (0.3048 m/ft) before every check.

Given: 50 kW general load, PF 0.85 lagging, 415 V three-phase, design factor 1.0. 50 mm² copper XLPE (90 °C) fixed multicore cable, 16 mm² earth, 300 ft; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 10.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 100 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 50.00 kW × 1000 / (√3 × 415 × 0.85) = 81.8 A
Check 1 — capacity	Base rating Table 14, column 2, row 50: 182 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 182 × 1.00 = 182.0 A vs I_design 81.8 A (loading 45.0 %) PASS
Check 2 — voltage drop	R_c = 0.494 Ω/km (Table 35), X_c = 0.0751 Ω/km (Table 30). At the design current, ΔV = √3 × 81.8 × 0.091 × (0.494 × 0.85 + 0.0751 × 0.527) = 5.96 V (drop) = 1.43 % of 415 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 50)² / 10,000² = 0.511 s vs 0.1 s; S_min = 10,000 × √0.1 / 143 = 22.1 mm² PASS
Check 4 — earth fault loop	Earth 16 mm²: R_e = 1.47, X_e = 0.0805 Ω/km (Table 30 at the earth size), Z_earth = 0.091 × √(1.47² + 0.0805²) = 0.1346 Ω. Z_loop = 0.03 + 0.0457 (phase) + 0.1346 (earth) = 0.2103 Ω. I_fault = 415/√3 / 0.2103 = 1,139 A vs 100 × 5 = 500 A; L_max = 228 m vs 91 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 81.8 A ≤ 100 A ≤ 182.0 A (device at 54.9 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 50 mm² phase conductor: 16 mm²; earth 16 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 415/√3 / 0.03 = 7,987 A. S_e,min = 7,987 × √0.04 (t_ef) / 143 = 11.17 mm² (k as the phase conductor, Table 52) vs 16 mm²; t_max = 0.082 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 908 W (1.81 %)

Example 37 — Auto-size a 75 kW feeder on a perforated tray

Automatic mode tries each standard size with its AS/NZS 3000 Table 5.1 earth until all seven checks pass.

Given: 75 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. Automatic sizing of a copper XLPE (90 °C) fixed multicore cable, 120 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 15.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 160 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 75.00 kW × 1000 / (√3 × 400 × 0.85) = 127.4 A
Sizes tried	1 (fails CCC, VD, SC, EFL, OVL, EWT), 1.5 (fails CCC, VD, SC, EFL, OVL, EWT), 2.5 (fails CCC, VD, SC, EFL, OVL, EWT), 4 (fails CCC, VD, SC, EFL, OVL, EWT), 6 (fails CCC, VD, SC, EFL, OVL, EWT), 10 (fails CCC, VD, SC, EFL, OVL, EWT), 16 (fails CCC, VD, SC, EFL, OVL, EWT), 25 (fails CCC, VD, SC, EFL, OVL, EWT), 35 (fails EFL, OVL, EWT), 50 (passes). Selected 50 mm² with a 16 mm² earth (AS/NZS 3000 Table 5.1).
Check 1 — capacity	Base rating Table 14, column 2, row 50: 182 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 182 × 1.00 = 182.0 A vs I_design 127.4 A (loading 70.0 %) PASS
Check 2 — voltage drop	R_c = 0.494 Ω/km (Table 35), X_c = 0.0751 Ω/km (Table 30). At the design current, ΔV = √3 × 127.4 × 0.120 × (0.494 × 0.85 + 0.0751 × 0.527) = 12.16 V (drop) = 3.04 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 50)² / 15,000² = 0.227 s vs 0.1 s; S_min = 15,000 × √0.1 / 143 = 33.2 mm² PASS
Check 4 — earth fault loop	Earth 16 mm²: R_e = 1.47, X_e = 0.0805 Ω/km (Table 30 at the earth size), Z_earth = 0.120 × √(1.47² + 0.0805²) = 0.1767 Ω. Z_loop = 0.03 + 0.0600 (phase) + 0.1767 (earth) = 0.2666 Ω. I_fault = 400/√3 / 0.2666 = 866 A vs 160 × 5 = 800 A; L_max = 131 m vs 120 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 127.4 A ≤ 160 A ≤ 182.0 A (device at 87.9 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 50 mm² phase conductor: 16 mm²; earth 16 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.03 = 7,698 A. S_e,min = 7,698 × √0.04 (t_ef) / 143 = 10.77 mm² (k as the phase conductor, Table 52) vs 16 mm²; t_max = 0.088 s PASS
Result	7/7 checks pass → PASS; governing criterion Earth Fault; power loss 2,884 W (3.85 %)

Example 38 — Auto-size 400 A on aluminium single-core cables

Automatic sizing with aluminium: small sizes the standard does not tabulate are skipped as unavailable.

Given: 400 A general load, 415 V three-phase, design factor 1.0. Automatic sizing of a aluminium XLPE (90 °C) fixed singlecore cable (trefoil), 60 m; unenclosed, spaced from surface & trefoil or flat touching, on ladder, racks or cleats, 1 circuit(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 25.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 400 A device with 5× instantaneous trip, source impedance 0.03 Ω, voltage-drop limit 5 %.

Load current	I_load = 400.0 A (specified)
Sizes tried	1 (not tabulated), 1.5 (not tabulated), 2.5 (not tabulated), 4 (not tabulated), 6 (not tabulated), 10 (not tabulated), 16 (not tabulated), 25 (not tabulated), 35 (not tabulated), 50 (fails CCC, VD, SC, EFL, OVL, EWT), 70 (fails CCC, VD, SC, EFL, OVL), 95 (fails CCC, EFL, OVL), 120 (fails CCC, OVL), 150 (fails CCC, OVL), 185 (passes). Selected 185 mm² with a 70 mm² earth (AS/NZS 3000 Table 5.1).
Check 1 — capacity	Base rating Table 8, column 4, row 185: 427 A. Derating Table 23, 18 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 427 × 1.00 = 427.0 A vs I_design 400.0 A (loading 93.7 %) PASS
Check 2 — voltage drop	R_c = 0.212 Ω/km (Table 34), X_c = 0.0835 Ω/km (Table 30). At the design current, ΔV = √3 × 400.0 × 0.060 × (0.212 × 0.85 + 0.0835 × 0.527) = 9.32 V (drop) = 2.25 % of 415 V, limit 5 % PASS
Check 3 — short circuit	k = 94 (Table 52). t_max = (94 × 185)² / 25,000² = 0.489 s vs 0.1 s; S_min = 25,000 × √0.1 / 94 = 83.7 mm² PASS
Check 4 — earth fault loop	Earth 70 mm²: R_e = 0.568, X_e = 0.0893 Ω/km (Table 30 at the earth size), Z_earth = 0.060 × √(0.568² + 0.0893²) = 0.0345 Ω. Z_loop = 0.03 + 0.0137 (phase) + 0.0345 (earth) = 0.0782 Ω. I_fault = 415/√3 / 0.0782 = 3,065 A vs 400 × 5 = 2,000 A; L_max = 112 m vs 60 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 400.0 A ≤ 400 A ≤ 427.0 A (device at 93.7 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 185 mm² phase conductor: 70 mm²; earth 70 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 415/√3 / 0.03 = 7,987 A. S_e,min = 7,987 × √0.04 (t_ef) / 94 = 16.90 mm² (k as the phase conductor, Table 52) vs 70 mm²; t_max = 0.686 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 6,106 W (2.50 %)

Example 39 — Auto-size a 30 kW pump-house feeder, 180 m direct buried

Capacity alone would allow 16 mm²; voltage drop rules that out, and the 6 mm² Table 5.1 earth of 25 mm² fails the earth-fault loop and its withstand, so 35 mm² is selected.

Given: 30 kW general load, PF 0.85 lagging, 400 V three-phase, design factor 1.0. Automatic sizing of a copper XLPE (90 °C) fixed multicore cable, 180 m; direct buried, 3 cable(s)/circuit(s) touching, depth 0.8 m, soil 1 K·m/W at 25 °C. Protection: prospective fault 6.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 63 A device with 5× instantaneous trip, source impedance 0.04 Ω, voltage-drop limit 5 %.

Load current	I_load = 30.00 kW × 1000 / (√3 × 400 × 0.85) = 50.9 A
Sizes tried	1 (fails CCC, VD, SC, EFL, OVL, EWT), 1.5 (fails CCC, VD, SC, EFL, OVL, EWT), 2.5 (fails CCC, VD, SC, EFL, OVL, EWT), 4 (fails CCC, VD, SC, EFL, OVL, EWT), 6 (fails CCC, VD, SC, EFL, OVL, EWT), 10 (fails CCC, VD, SC, EFL, OVL, EWT), 16 (fails VD, EFL, EWT), 25 (fails EFL, EWT), 35 (passes). Selected 35 mm² with a 10 mm² earth (AS/NZS 3000 Table 5.1).
Check 1 — capacity	Base rating Table 14, column 23, row 35: 172 A. Derating Table 25(2), column 2, row 3: 0.700; Table 27(2), 90 °C conductor column, row 25: 1.00; Table 28(1), column 2, row 0.8: 0.970; Table 29, column 2, row 1: 1.04 → F = 0.706. I_derated = 172 × 0.706 = 121.5 A vs I_design 50.9 A (loading 41.9 %) PASS
Check 2 — voltage drop	R_c = 0.669 Ω/km (Table 35), X_c = 0.0786 Ω/km (Table 30). At the design current, ΔV = √3 × 50.9 × 0.180 × (0.669 × 0.85 + 0.0786 × 0.527) = 9.69 V (drop) = 2.42 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 35)² / 6,000² = 0.696 s vs 0.1 s; S_min = 6,000 × √0.1 / 143 = 13.3 mm² PASS
Check 4 — earth fault loop	Earth 10 mm²: R_e = 2.33, X_e = 0.0840 Ω/km (Table 30 at the earth size), Z_earth = 0.180 × √(2.33² + 0.0840²) = 0.4197 Ω. Z_loop = 0.04 + 0.1212 (phase) + 0.4197 (earth) = 0.5809 Ω. I_fault = 400/√3 / 0.5809 = 398 A vs 63 × 5 = 315 A; L_max = 231 m vs 180 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 50.9 A ≤ 63 A ≤ 121.5 A (device at 51.9 % of cable capacity) PASS
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 35 mm² phase conductor: 10 mm²; earth 10 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.04 = 5,774 A. S_e,min = 5,774 × √0.04 (t_ef) / 143 = 8.07 mm² (k as the phase conductor, Table 52) vs 10 mm²; t_max = 0.061 s PASS
Result	7/7 checks pass → PASS; governing criterion Overload; power loss 938 W (3.12 %)

Example 40 — Auto-size 500 kW over 400 m: no single cable passes

When no standard size satisfies every check the largest available size is reported with its failures.

Given: 500 kW general load, PF 0.9 lagging, 400 V three-phase, design factor 1.0. Automatic sizing of a copper XLPE (90 °C) fixed multicore cable, 400 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C. Protection: prospective fault 36.0 kA cleared in 0.1 s, earth-fault clearing time 0.04 s, 1000 A device with 5× instantaneous trip, source impedance 0.02 Ω, voltage-drop limit 5 %.

Load current	I_load = 500.00 kW × 1000 / (√3 × 400 × 0.9) = 801.9 A
Sizes tried	1 (fails CCC, VD, SC, EFL, OVL, EWT), 1.5 (fails CCC, VD, SC, EFL, OVL, EWT), 2.5 (fails CCC, VD, SC, EFL, OVL, EWT), 4 (fails CCC, VD, SC, EFL, OVL, EWT), 6 (fails CCC, VD, SC, EFL, OVL, EWT), 10 (fails CCC, VD, SC, EFL, OVL, EWT), 16 (fails CCC, VD, SC, EFL, OVL, EWT), 25 (fails CCC, VD, SC, EFL, OVL, EWT), 35 (fails CCC, VD, SC, EFL, OVL, EWT), 50 (fails CCC, VD, SC, EFL, OVL, EWT), 70 (fails CCC, VD, SC, EFL, OVL), 95 (fails CCC, VD, EFL, OVL), 120 (fails CCC, VD, EFL, OVL), 150 (fails CCC, VD, EFL, OVL), 185 (fails CCC, VD, EFL, OVL), 240 (fails CCC, VD, EFL, OVL), 300 (fails CCC, VD, EFL, OVL), 400 (fails CCC, VD, EFL, OVL), 500 (fails CCC, VD, EFL, OVL), 630 (not tabulated). No size passes; largest available size 500 mm² shown.
Check 1 — capacity	Base rating Table 14, column 2, row 500: 794 A. Derating Table 24, 10 °C conductor column, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 794 × 1.00 = 794.0 A vs I_design 801.9 A (loading 101.0 %) FAIL
Check 2 — voltage drop	R_c = 0.0544 Ω/km (Table 35), X_c = 0.0700 Ω/km (Table 30). At the design current, ΔV = √3 × 801.9 × 0.400 × (0.0544 × 0.9 + 0.0700 × 0.436) = 44.15 V (drop) = 11.04 % of 400 V, limit 5 % FAIL
Check 3 — short circuit	k = 143 (Table 52). t_max = (143 × 500)² / 36,000² = 3.945 s vs 0.1 s; S_min = 36,000 × √0.1 / 143 = 79.6 mm² PASS
Check 4 — earth fault loop	Earth 120 mm²: R_e = 0.197, X_e = 0.0713 Ω/km (Table 30 at the earth size), Z_earth = 0.400 × √(0.197² + 0.0713²) = 0.0838 Ω. Z_loop = 0.02 + 0.0355 (phase) + 0.0838 (earth) = 0.1393 Ω. I_fault = 400/√3 / 0.1393 = 1,658 A vs 1000 × 5 = 5,000 A; L_max = 88 m vs 400 m FAIL
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 801.9 A ≤ 1,000 A ≤ 794.0 A (device at 125.9 % of cable capacity) FAIL
Check 6 — earth conductor size	AS/NZS 3000:2018 Table 5.1 minimum for a 500 mm² phase conductor: 120 mm²; earth 120 mm² PASS
Check 7 — earth conductor withstand	Earth fault at the cable origin: I_ef = 400/√3 / 0.02 = 11,547 A. S_e,min = 11,547 × √0.04 (t_ef) / 143 = 16.15 mm² (k as the phase conductor, Table 52) vs 120 mm²; t_max = 2.208 s PASS
Result	3/7 checks pass → FAIL; governing criterion Earth Fault; power loss 41,975 W (8.39 %). Derated capacity (794.0A) < Design current (801.9A); Voltage drop (11.04%) > Maximum allowed (5%); Insufficient fault current: 1658.3A < 5000.0A; Cable too long: 400.0m > 87.8m; Device rating (1000A) > Derated capacity (794.0A)

Validation corpus examples

The 4 examples below are the validation cases for this calculation. Each one was produced by the calculation engine from the inputs shown, every figure was checked against the independent reference quoted at the end of the example, and the same cases are run against every engine build (see validation scorecard, tool fe_calc_cable_size; worked examples for every calculation).

#	Case	Cable	I_design (A)	I_derated (A)	V_d (%)	Governing	Result
1	90 kW feeder, 100 m, auto-sized on the derived 160 A device	70 mm² Cu XLPE (auto)	152.8	230.0	2.19	overcurrent device coordination	PASS
2	Check 35 mm² for 100 A over 70 m on a 100 A device	35 mm² Cu XLPE	100.0	144.0	1.85	overcurrent device coordination	PASS
3	Check 35 mm² with a 6 mm² earth: below the Table 5.1 minimum	35 mm² Cu XLPE	100.0	144.0	1.85	earth conductor size (AS/NZS 3000 Table 5.1)	FAIL
4	50 mm² behind a 0.02 Ω loop, 0.4 s backup clearing: earth withstand fails	50 mm² Cu XLPE	150.0	182.0	1.79	earth conductor thermal withstand	FAIL

Example 1 — 90 kW feeder, 100 m, auto-sized on the derived 160 A device

No device rating is given, so the next standard rating above the 152.8 A design current (160 A) is assumed; 50 mm² carries the load but its 16 mm² earth fails the 800 A loop requirement, so 70 mm² with its 25 mm² Table 5.1 earth is selected, and I_B/I_N = 95.5 % makes overload coordination govern.

Given: 90 kW three-phase load at 400 V, PF 0.85 (default) lagging, design factor 1 (default). Auto sizing of a copper XLPE (X-90) fixed multicore cable, route 100 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C (default). Protection: prospective fault 10 kA (default) cleared in 0.1 s (default), earth-fault clearing time 0.04 s (default), 160 A device (derived: next standard rating above the design current) with 5× instantaneous trip (default), upstream loop impedance 0.1 Ω (default), voltage-drop limit 5 % (default). AS/NZS 3008.1.1:2017 tables.

Load current	I_load = 90 kW × 1000 / (√3 × 400 × 0.85) = 152.83 A; design factor 1.0 → I_design = 152.83 A
Sizes tried	1 (fails CCC, VD, SC, EFL, OVL, EWT), 1.5 (fails CCC, VD, SC, EFL, OVL, EWT), 2.5 (fails CCC, VD, SC, EFL, OVL, EWT), 4 (fails CCC, VD, SC, EFL, OVL, EWT), 6 (fails CCC, VD, SC, EFL, OVL, EWT), 10 (fails CCC, VD, SC, EFL, OVL), 16 (fails CCC, VD, SC, EFL, OVL), 25 (fails CCC, VD, EFL, OVL), 35 (fails CCC, EFL, OVL), 50 (fails EFL), 70 (passes). Selected 70 mm² with a 25 mm² earth.
Check 1 — capacity	Base rating Table 14, column 2, row 70: 230 A. Derating Table 24, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 230 × 1.00 = 230.00 A vs I_design 152.83 A (loading 66.4 %) PASS
Check 2 — voltage drop	R_c = 0.343 Ω/km (Ref: Table 35, Column 5, Row: 70mm²), X_c = 0.0741 Ω/km (Ref: Table 30, Column 10, Row: 70mm²). At the design current: ΔV = √3 × 152.83 × 0.100 × (0.343 × 0.85 + 0.0741 × 0.527) = 8.75 V (drop) = 2.19 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52, Cu 90 → 250 °C). t_max = (143 × 70)² / 10,000² = 1.0020 s vs 0.1 s clearing; S_min = 10,000 × √0.1 / 143 = 22.11 mm² PASS
Check 4 — earth fault loop	Z_s = Z_ext + L·√(R_c² + X_c²) + L·√(R_e² + X_e²) with the earth's R_e = 0.927 Ω/km and X_e = 0.0808 Ω/km (Table 30 at 25 mm²): Z_s = 0.1 + 0.0351 (phase) + 0.0931 (earth) = 0.2281 Ω vs Z_s,max = 400/√3 / (160 × 5) = 0.2887 Ω; I_fault = 230.9 / 0.2281 = 1,012 A vs 800 A PASS. L_max = (0.2887 − 0.1) / 1.281 Ω/km = 147.2 m vs 100 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 152.83 A ≤ 160 A ≤ 230.00 A (device at 69.6 % of cable capacity) PASS
Check 6 — earth size	AS/NZS 3000 Table 5.1 minimum for a 70 mm² phase conductor: 25 mm²; earth 25 mm² PASS
Check 7 — earth withstand	Largest earth-fault current, a fault at the cable origin: I_ef = 400/√3 / 0.1 = 2,309 A, cleared in t_ef = 0.04 s (default: a fault at the origin is far above the device's instantaneous threshold, so it clears instantaneously). k = 143 (integral earth core: the phase conductor's Table 52 k). S_min = I_ef × √t_ef / k = 2,309 × √0.04 / 143 = 3.23 mm² vs 25 mm² (t_max = (143 × 25 / 2,309)² = 2.3964 s) PASS
Result	8/8 checks pass → PASS; 70 mm² Cu with 25 mm² earth; power loss 2,403 W (2.67 %); governing: ocpd coordination
Reference	Hand calculation: I = 90 kW / (√3 × 400 V × 0.85) = 152.83 A (formula as calcs/test_c0030 TestCalculateLoadCurrent); no device rating given, so the tool assumes the next standard rating above 152.83 A, 160 A, and the loop must drive 5 × 160 = 800 A: Zs,max = (400/√3)/800 = 0.2887 Ω. With AS/NZS 3008.1.1:2017 Table 35/30 values (earth reactance from Table 30 at the earth size), 50 mm² + 16 mm² earth (AS/NZS 3000 Table 5.1) over 100 m gives Zs = 0.1 + 0.1·√(0.494² + 0.0751²) + 0.1·√(1.47² + 0.0805²) = 0.1 + 0.0500 + 0.1472 = 0.2972 Ω > 0.2887 Ω (fails) and 70 mm² + 25 mm² gives Zs = 0.1 + 0.1·√(0.343² + 0.0741²) + 0.1·√(0.927² + 0.0808²) = 0.1 + 0.0351 + 0.0931 = 0.2281 Ω (passes, I_ef = 1012.3 A, Lmax = 147.2 m); Table 14 col 2 rating for 70 mm² = 230 A ≥ 152.83 A; ΔV = √3 × 152.83 × 0.1 × (0.343 × 0.85 + 0.0741 × 0.527) = 8.75 V = 2.19 % (design factor 1, so the design current); earth withstand I_ef = (400/√3)/0.1 = 2309 A cleared in the default t_ef = 0.04 s, S_min = 2309 × √0.04 / 143 = 3.23 mm² ≤ 25 mm²; I_B 152.83 A ≤ I_N 160 A ≤ I_Z 230 A, and I_B/I_N = 95.5 % is the highest utilisation, so overload coordination governs. (validation case `c0030-90kw-400v-100m-auto`)

Example 2 — Check 35 mm² for 100 A over 70 m on a 100 A device

Check mode with all seven checks passing; the device rating equals the 100 A design current, so overload coordination is the governing criterion at 100 % utilisation.

Given: three-phase load of 100 A at 400 V, PF 0.85 (default) lagging (for voltage drop), design factor 1 (default). Check 35 mm² copper XLPE (X-90) fixed multicore cable with a 10 mm² earth (AS/NZS 3000 Table 5.1), route 70 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C (default). Protection: prospective fault 10 kA (default) cleared in 0.1 s (default), earth-fault clearing time 0.04 s (default), 100 A device with 5× instantaneous trip (default), upstream loop impedance 0.1 Ω (default), voltage-drop limit 5 % (default). AS/NZS 3008.1.1:2017 tables.

Load current	I_load = 100.00 A (given); design factor 1.0 → I_design = 100.00 A
Check 1 — capacity	Base rating Table 14, column 2, row 35: 144 A. Derating Table 24, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 144 × 1.00 = 144.00 A vs I_design 100.00 A (loading 69.4 %) PASS
Check 2 — voltage drop	R_c = 0.669 Ω/km (Ref: Table 35, Column 5, Row: 35mm²), X_c = 0.0786 Ω/km (Ref: Table 30, Column 10, Row: 35mm²). At the design current: ΔV = √3 × 100.00 × 0.070 × (0.669 × 0.85 + 0.0786 × 0.527) = 7.40 V (drop) = 1.85 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52, Cu 90 → 250 °C). t_max = (143 × 35)² / 10,000² = 0.2505 s vs 0.1 s clearing; S_min = 10,000 × √0.1 / 143 = 22.11 mm² PASS
Check 4 — earth fault loop	Z_s = Z_ext + L·√(R_c² + X_c²) + L·√(R_e² + X_e²) with the earth's R_e = 2.33 Ω/km and X_e = 0.0840 Ω/km (Table 30 at 10 mm²): Z_s = 0.1 + 0.0472 (phase) + 0.1632 (earth) = 0.3104 Ω vs Z_s,max = 400/√3 / (100 × 5) = 0.4619 Ω; I_fault = 230.9 / 0.3104 = 744 A vs 500 A PASS. L_max = (0.4619 − 0.1) / 3.005 Ω/km = 120.4 m vs 70 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 100.00 A ≤ 100 A ≤ 144.00 A (device at 69.4 % of cable capacity) PASS
Check 6 — earth size	AS/NZS 3000 Table 5.1 minimum for a 35 mm² phase conductor: 10 mm²; earth 10 mm² PASS
Check 7 — earth withstand	Largest earth-fault current, a fault at the cable origin: I_ef = 400/√3 / 0.1 = 2,309 A, cleared in t_ef = 0.04 s (default: a fault at the origin is far above the device's instantaneous threshold, so it clears instantaneously). k = 143 (integral earth core: the phase conductor's Table 52 k). S_min = I_ef × √t_ef / k = 2,309 × √0.04 / 143 = 3.23 mm² vs 10 mm² (t_max = (143 × 10 / 2,309)² = 0.3834 s) PASS
Result	8/8 checks pass → PASS; 35 mm² Cu with 10 mm² earth; power loss 1,405 W (2.39 %); governing: ocpd coordination
Reference	Hand calculation with AS/NZS 3008.1.1:2017 Table 35/Table 30 values (35 mm² phase, 10 mm² Table 5.1 earth; the earth's reactance from Table 30 at 10 mm²): ΔV = √3·100·0.07·(0.669·0.85 + 0.0786·0.527) = 7.40 V = 1.85 %; Zs = 0.1 + \|Z35\|·0.07 + \|Z10\|·0.07 = 0.1 + 0.07·√(0.669² + 0.0786²) + 0.07·√(2.33² + 0.084²) = 0.1 + 0.0472 + 0.1632 = 0.3104 Ω ≤ (400/√3)/(5 × 100 A) = 0.4619 Ω; maximum length on the same loop model Lmax = (0.4619 − 0.1)/(0.6736 + 2.3315 Ω/km) = 120.4 m; withstand t = (143 × 35 / 10 000)² = 0.2505 s; earth: 10 mm² = Table 5.1 minimum, adiabatic S_min = (400/√3)/0.1 × √0.04 / 143 = 3.23 mm² ≤ 10 mm² (near-end fault cleared instantaneously, default t_ef = 0.04 s); overload coordination I_B 100 A ≤ I_N 100 A ≤ I_Z 144 A passes at 100 % device utilisation, the highest of the seven criteria, so it governs. (validation case `c0030-check-35mm2-100a-70m`)

Example 3 — Check 35 mm² with a 6 mm² earth: below the Table 5.1 minimum

Check mode with a user-supplied earth one size below the AS/NZS 3000 Table 5.1 minimum (10 mm² for 35 mm²): the loop impedance and the earth's adiabatic withstand pass, but the earth size check fails and governs.

Given: three-phase load of 100 A at 400 V, PF 0.85 (default) lagging (for voltage drop), design factor 1 (default). Check 35 mm² copper XLPE (X-90) fixed multicore cable with a 6 mm² earth, route 70 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C (default). Protection: prospective fault 10 kA (default) cleared in 0.1 s (default), earth-fault clearing time 0.04 s (default), 100 A device with 5× instantaneous trip (default), upstream loop impedance 0.1 Ω (default), voltage-drop limit 5 % (default). AS/NZS 3008.1.1:2017 tables.

Load current	I_load = 100.00 A (given); design factor 1.0 → I_design = 100.00 A
Check 1 — capacity	Base rating Table 14, column 2, row 35: 144 A. Derating Table 24, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 144 × 1.00 = 144.00 A vs I_design 100.00 A (loading 69.4 %) PASS
Check 2 — voltage drop	R_c = 0.669 Ω/km (Ref: Table 35, Column 5, Row: 35mm²), X_c = 0.0786 Ω/km (Ref: Table 30, Column 10, Row: 35mm²). At the design current: ΔV = √3 × 100.00 × 0.070 × (0.669 × 0.85 + 0.0786 × 0.527) = 7.40 V (drop) = 1.85 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52, Cu 90 → 250 °C). t_max = (143 × 35)² / 10,000² = 0.2505 s vs 0.1 s clearing; S_min = 10,000 × √0.1 / 143 = 22.11 mm² PASS
Check 4 — earth fault loop	Z_s = Z_ext + L·√(R_c² + X_c²) + L·√(R_e² + X_e²) with the earth's R_e = 3.93 Ω/km and X_e = 0.0887 Ω/km (Table 30 at 6 mm²): Z_s = 0.1 + 0.0472 (phase) + 0.2752 (earth) = 0.4223 Ω vs Z_s,max = 400/√3 / (100 × 5) = 0.4619 Ω; I_fault = 230.9 / 0.4223 = 547 A vs 500 A PASS. L_max = (0.4619 − 0.1) / 4.605 Ω/km = 78.6 m vs 70 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 100.00 A ≤ 100 A ≤ 144.00 A (device at 69.4 % of cable capacity) PASS
Check 6 — earth size	AS/NZS 3000 Table 5.1 minimum for a 35 mm² phase conductor: 10 mm²; earth 6 mm² FAIL
Check 7 — earth withstand	Largest earth-fault current, a fault at the cable origin: I_ef = 400/√3 / 0.1 = 2,309 A, cleared in t_ef = 0.04 s (default: a fault at the origin is far above the device's instantaneous threshold, so it clears instantaneously). k = 143 (integral earth core: the phase conductor's Table 52 k). S_min = I_ef × √t_ef / k = 2,309 × √0.04 / 143 = 3.23 mm² vs 6 mm² (t_max = (143 × 6 / 2,309)² = 0.1380 s) PASS
Result	7/8 checks pass → FAIL; 35 mm² Cu with 6 mm² earth; power loss 1,405 W (2.39 %); governing: earth conductor size. Earth fault trip margin is very low (1.09x) Review protection settings - fault current barely exceeds trip threshold
Reference	Hand calculation with AS/NZS 3008.1.1:2017 Table 35/30 values (35 mm² phase, 6 mm² earth): AS/NZS 3000 Table 5.1 requires 10 mm² for a 35 mm² copper active, so 6 mm² fails the size check (10/6 = 167 %, the governing criterion); the loop still passes: Zs = 0.1 + 0.07·√(0.669² + 0.0786²) + 0.07·√(3.93² + 0.0887²) = 0.1 + 0.0472 + 0.2752 = 0.4223 Ω ≤ (400/√3)/(5 × 100 A) = 0.4619 Ω, Lmax = (0.4619 − 0.1)/(0.6736 + 3.9310 Ω/km) = 78.6 m; earth withstand I_ef = (400/√3)/0.1 = 2309 A cleared in the default t_ef = 0.04 s, S_min = 2309·√0.04/143 = 3.23 mm² ≤ 6 mm²; ΔV = √3·100·0.07·(0.669·0.85 + 0.0786·0.527) = 7.40 V = 1.85 %; withstand t = (143 × 35 / 10 000)² = 0.2505 s; I_B 100 A ≤ I_N 100 A ≤ I_Z 144 A. (validation case `c0030-check-35mm2-earth-6mm2-below-table-5-1`)

Example 4 — 50 mm² behind a 0.02 Ω loop, 0.4 s backup clearing: earth withstand fails

A stiff upstream loop drives 11.5 kA into an earth fault at the cable origin; if the design relies on a 0.4 s upstream backup to clear it (earth_fault_clearing_time_s = 0.4) the earth needs 51 mm², so the 16 mm² Table 5.1 earth fails although the 50 mm² phase withstands the 10 kA prospective fault.

Given: three-phase load of 150 A at 400 V, PF 0.85 (default) lagging (for voltage drop), design factor 1 (default). Check 50 mm² copper XLPE (X-90) fixed multicore cable with a 16 mm² earth (AS/NZS 3000 Table 5.1), route 60 m; unenclosed, spaced from surface, on perforated trays horizontal, 1 cable(s) per tier, 1 tier(s), spaced, air ambient 40 °C (default). Protection: prospective fault 10 kA cleared in 0.4 s, earth-fault clearing time 0.4 s, 160 A device with 5× instantaneous trip (default), upstream loop impedance 0.02 Ω, voltage-drop limit 5 % (default). AS/NZS 3008.1.1:2017 tables.

Load current	I_load = 150.00 A (given); design factor 1.0 → I_design = 150.00 A
Check 1 — capacity	Base rating Table 14, column 2, row 50: 182 A. Derating Table 24, row 1: 1.00; Table 27(1), 90 °C conductor column, row 40: 1.00 → F = 1.00. I_derated = 182 × 1.00 = 182.00 A vs I_design 150.00 A (loading 82.4 %) PASS
Check 2 — voltage drop	R_c = 0.494 Ω/km (Ref: Table 35, Column 5, Row: 50mm²), X_c = 0.0751 Ω/km (Ref: Table 30, Column 10, Row: 50mm²). At the design current: ΔV = √3 × 150.00 × 0.060 × (0.494 × 0.85 + 0.0751 × 0.527) = 7.16 V (drop) = 1.79 % of 400 V, limit 5 % PASS
Check 3 — short circuit	k = 143 (Table 52, Cu 90 → 250 °C). t_max = (143 × 50)² / 10,000² = 0.5112 s vs 0.4 s clearing; S_min = 10,000 × √0.4 / 143 = 44.23 mm² PASS
Check 4 — earth fault loop	Z_s = Z_ext + L·√(R_c² + X_c²) + L·√(R_e² + X_e²) with the earth's R_e = 1.47 Ω/km and X_e = 0.0805 Ω/km (Table 30 at 16 mm²): Z_s = 0.02 + 0.0300 (phase) + 0.0883 (earth) = 0.1383 Ω vs Z_s,max = 400/√3 / (160 × 5) = 0.2887 Ω; I_fault = 230.9 / 0.1383 = 1,670 A vs 800 A PASS. L_max = (0.2887 − 0.02) / 1.972 Ω/km = 136.3 m vs 60 m PASS
Check 5 — overload coordination	I_B ≤ I_N ≤ I_Z: 150.00 A ≤ 160 A ≤ 182.00 A (device at 87.9 % of cable capacity) PASS
Check 6 — earth size	AS/NZS 3000 Table 5.1 minimum for a 50 mm² phase conductor: 16 mm²; earth 16 mm² PASS
Check 7 — earth withstand	Largest earth-fault current, a fault at the cable origin: I_ef = 400/√3 / 0.02 = 11,547 A, cleared in t_ef = 0.4 s (given: the upstream backup clearing time the design relies on). k = 143 (integral earth core: the phase conductor's Table 52 k). S_min = I_ef × √t_ef / k = 11,547 × √0.4 / 143 = 51.07 mm² vs 16 mm² (t_max = (143 × 16 / 11,547)² = 0.0393 s) FAIL
Result	7/8 checks pass → FAIL; 50 mm² Cu with 16 mm² earth; power loss 2,001 W (2.27 %); governing: earth conductor withstand. Cable utilization is elevated (82.4%) - monitor for load changes The upstream earth-loop impedance (0.02 Ω) gives 11547 A of earth-fault current at the cable origin, more than the 10 kA prospective fault: the two inputs are inconsistent Check the upstream loop impedance against the prospective fault level; the earth withstand check uses the loop impedance
Reference	Hand calculation: near-end earth fault I_ef = (400/√3)/0.02 Ω = 11 547 A; with the given 0.4 s backup earth-fault clearing time the adiabatic minimum earth S_min = I_ef·√t_ef/k = 11 547 × √0.4 / 143 = 51.07 mm² (k = 143, AS/NZS 3008.1.1:2017 Table 52, 90 °C row, shared with the phase core) > 16 mm² (the AS/NZS 3000 Table 5.1 earth for 50 mm²), so earth withstand fails at 319 % and governs (at the default instantaneous 0.04 s it would need 16.15 mm², still just above 16 mm²); the phase core passes: t = (143 × 50 / 10 000)² = 0.5112 s ≥ 0.4 s; with Table 14/35/30 values I_Z = 182 A ≥ 150 A, ΔV = √3·150·0.06·(0.494·0.85 + 0.0751·0.527) = 7.16 V = 1.79 %, Zs = 0.02 + 0.06·√(0.494² + 0.0751²) + 0.06·√(1.47² + 0.0805²) = 0.02 + 0.0300 + 0.0883 = 0.1383 Ω ≤ (400/√3)/(5 × 160) = 0.2887 Ω; I_B 150 A ≤ I_N 160 A ≤ I_Z 182 A. (validation case `c0030-check-50mm2-0p02ohm-0p4s-earth-withstand-fails`)

Combinations the installed edition does not tabulate are reported rather than approximated: cables exposed to the sun, aluminium with EPR insulation, and sizes the standard leaves blank (for example multicore above 500 mm² or aluminium below 16 mm²) return a “does not rate” message that names the table, the selection it rejects and the input to change (for example an air ambient above the insulation rating, or a laying depth the depth table has no row for). Any edition other than 2017 is rejected with a 422 validation error naming the field.

Standards & References

AS/NZS 3008.1.1:2017 — Electrical installations — Selection of cables — Cables for alternating voltages up to and including 0.6/1 kV
- Tables 4–15 — Current-carrying capacity for single-core and multicore cables at 75, 90 and 110 °C
- Tables 22–26 — Grouping derating: bunched, trays and ladders, direct buried, buried conduits
- Table 27 — Air and soil ambient temperature derating
- Table 28 — Depth of laying derating
- Table 29 — Soil thermal resistivity derating
- Tables 30–32 — Reactance at 50 Hz (fixed, flexible and MIMS cables)
- Tables 34–38 — AC resistance at 50 Hz by conductor temperature
- Table 52 — Short-circuit temperature-rise constant k (adiabatic equation, phase and earth conductor)
AS/NZS 3000:2018 — Wiring Rules
- Clause 3.6 — Voltage drop limits
- Clause 2.5 — Overload and short-circuit protection of conductors
- Clause 5.7 and Appendix B — Earth fault loop impedance and disconnection times
- Table 5.1 — Minimum earth conductor size (Check 6, and the earth chosen by automatic sizing)
IEC 60364 — Low-voltage electrical installations — general principles for earth fault loop impedance verification

Tips & Limitations

Tips

Use specify by current when you already know the load current from equipment data sheets or metering, or when the load is not purely resistive/reactive and the simple P/(sqrt(3)*V*PF) formula does not apply.
The design factor defaults to 1.0 for general loads. Consider increasing it to 1.1–1.2 for loads expected to grow, or for loads with intermittent overload characteristics (e.g., welding).
Check 1 (CCC) typically drives the cable size up; Check 2 (VD) is more critical on long runs; Check 3 (SC) on high fault level installations; Check 4 (EFL) on long runs with high source impedance; Check 5 fails when the breaker chosen for the load is larger than the derated cable can tolerate, so in automatic mode the breaker rating itself can set the cable size; Check 7 fails on strong sources with slow clearing, where the Table 5.1 earth is too small for the origin earth-fault current.
For VSD supply cables, harmonic derating is not applied automatically — consider manually increasing the design factor to account for harmonic currents.
Underground cables accumulate multiple derating factors (grouping, burial depth, soil resistivity, ground temperature) — the combined effect can reduce capacity by 40% or more.
Aluminium cables have approximately 1.6× the resistance of copper — typically require one size larger for equivalent performance.
If Check 4 (EFL) fails, consider reducing the earth conductor impedance (increase earth conductor size) or reducing source impedance.
If Check 7 (earth withstand) fails, enter a larger earth conductor than the Table 5.1 minimum or check the earth-fault clearing time; a larger phase conductor alone only helps where its Table 5.1 earth is larger.
A warning that the inputs are inconsistent means \(V_{ph} / Z_{source}\) is larger than the prospective fault current: an earth fault at the origin cannot exceed the three-phase fault, so one of the two inputs is wrong. Check 7 uses the loop impedance, so correct whichever is wrong before relying on it.
The 5% voltage drop default is common for sub-mains per AS/NZS 3000; some installations may require tighter limits (e.g., 2.5% for final sub-circuits).

Limitations

Three-phase only — this calculator is for three-phase non-motor loads. Use c0031 for single-phase load cable sizing or c0006 / c0032 for motor cable sizing.
No motor efficiency — the current formula does not include an efficiency term. For motor loads where efficiency must be accounted for, use the motor cable sizing calculator (c0006) instead.
Tabulated conditions only — ambient temperatures, depths, soil resistivities and circuit counts are the standard's table rows; the inputs are lists for that reason and no interpolation is performed.
Overload device characteristics — Check 5 compares ratings only; it assumes the device's conventional operating current satisfies \(I_2 \le 1.45\,I_Z\), which holds for devices to AS/NZS 60898, AS/NZS 60947.2 and AS 60269.
MIMS cables — resistance and reactance come from Tables 38 and 32 (0.6/1 kV multicore, 1–2.5 mm² only), but the current rating is taken from the plastic-insulated table for the chosen insulation temperature. Treat MIMS results as indicative.
Low-voltage cables only — the tables cover 0.6/1 kV cables. Voltages above 1 kV in the list are not supported by this data; use the HV cable sizing calculator (c0020).
Balanced system assumed — the calculator assumes balanced three-phase loading. Unbalanced phase loading is not modelled.
Single-core spacing — AS/NZS 3008 Table 30 tabulates single-core reactance only for trefoil and flat touching arrangements. Single-core cables with the conductors spaced (unenclosed) or one conductor per conduit (Dedicated conduit) are therefore rejected with an explanatory error rather than given the touching reactance, which would understate the voltage drop and loop impedance.
Earth fault loop — the earth conductor's resistance and reactance are both included, at the insulation operating temperature; the phasor angles are not used (magnitudes add) and no allowance is made for the conductor heating during the fault.
Earth conductor withstand — Check 7 uses the near-end earth-fault current \(V_{ph}/Z_{source}\) and the earth-fault clearing time input, not the protection time of Check 3; a separately run (non-integral) earth with a different initial temperature would have a different \(k\) and is not modelled.
Harmonic currents — not considered. For loads with significant harmonics (VSD supplies, LED lighting boards, UPS systems), additional cable derating may be required.

Developer Guide

Architecture

File layout:

components/c0030_load_cable_sizing/component.py — Component registration, parameter schema, equation builder, summary cards builder
components/c0030_load_cable_sizing/calculations.py — Load current calculation, CCC check with webcalcs, parameter mapping to webcalcs format
components/c0030_load_cable_sizing/equations.py — MathJax equation builder for PDF report generation
components/c0030_load_cable_sizing/excel_generator.py — Excel report generator (openpyxl) with all seven checks
components/c0030_load_cable_sizing/templates/.../sidebar_form.html — Sidebar input form template

The calculator class is LoadCableSizingCalculator, registered as load_cable_sizing via register_component(). It extends ElectricalCalculator (from calcs.core.base_calculator).

Shared functions from calcs.core.cable_utils: This component imports several functions from the shared cable utilities module:

HP_TO_KW — HP to kW conversion constant (0.7457)
SQRT_3 — Square root of 3 constant
call_webcalcs_api — Internal webcalcs API call
check_earth_fault_loop — Check 4 (EFL) calculation
check_overload_coordination — Check 5 (AS/NZS 3000 Cl. 2.5.3.1)
check_earth_conductor_size — Check 6 (AS/NZS 3000 Table 5.1)
check_earth_conductor_withstand — Check 7 (adiabatic, Table 52 k)
check_short_circuit — Check 3 (SC) adiabatic equation
check_voltage_drop_with_webcalcs — Check 2 (VD) using webcalcs results
convert_length_to_meters — Length unit conversion

Webcalcs integration: Checks 1 and 2 use the webcalcs API (call_webcalcs_api) for AS/NZS 3008 standard table lookups. Checks 3 and 4 use local calculation functions from calcs.core.cable_utils. map_calcs_to_webcalcs_params_load() translates c0030 parameter names to the webcalcs format, setting loadtype='Load' and efficiency=100 (no motor efficiency).

Key difference from c0006: The CCC check (check_current_capacity_with_webcalcs_load) uses the configurable design_factor (default 1.0) instead of the motor calculator’s hardcoded 1.25× multiplier.

Code Paths

Key functions in calculations.py:

Function	Purpose
`calculate_load_cable_sizing(data)`	Main entry point — orchestrates all seven checks and returns combined results
`calculate_load_current(power, voltage, pf, power_type)`	Load current calculation (no efficiency term)
`check_current_capacity_with_webcalcs_load(data, webcalcs_results)`	Check 1: CCC using webcalcs API results with configurable design factor
`map_calcs_to_webcalcs_params_load(data)`	Translate c0030 parameters to webcalcs API format (loadtype=’Load’)

Shared functions from calcs.core.cable_utils:

Function	Purpose
`check_voltage_drop_with_webcalcs(data, webcalcs_results)`	Check 2: Voltage drop using webcalcs API results
`check_short_circuit(data)`	Check 3: Adiabatic short circuit withstand (local calc)
`check_earth_fault_loop(data)`	Check 4: Earth fault loop impedance (local calc)
`check_overload_coordination(data, check1_ccc)`	Check 5: Device rating between design current and derated capacity
`check_earth_conductor_size(data)`	Check 6: Earth conductor against the AS/NZS 3000 Table 5.1 minimum
`check_earth_conductor_withstand(data, k_override, phases, table_reference)`	Check 7: Adiabatic withstand of the earth under the origin earth-fault current
`call_webcalcs_api(calcVals)`	Internal call to webcalcs RunCalculation endpoint
`convert_length_to_meters(length, unit)`	Length unit conversion

Request flow:

LoadCableSizingCalculator.validate_parameters() validates inputs (checks specify_by mode)
LoadCableSizingCalculator.calculate() assembles data dict and calls calculate_load_cable_sizing(data)
If specify_by = ‘power’, current is computed via calculate_load_current(); if ‘current’, the user-specified value is used directly
Design current = full load current × design factor
Parameters are mapped to webcalcs format via map_calcs_to_webcalcs_params_load()
Webcalcs API is called for CCC and VD table lookups
All seven checks run and results are aggregated into overall pass/fail
equation_builder() converts results to unified article format for PDF output

Testing

Running tests:

pytest calcs/test_c0030_load_cable_sizing.py calcs/test_c0030_help_examples.py -v

Worked examples: the 40 examples above are defined in components/c0030_load_cable_sizing/help_examples.py and rendered into help/_load_cable_sizing_examples.html by python manage.py generate_c0030_help_examples, which also recomputes every figure independently of the engine. test_c0030_help_examples.py re-runs the cases against the installed tables (it skips where the 2017 data is absent) and fails if the committed fragment is stale.

The “Validation corpus examples” beneath them come from mcp_public/validation/cases/fe_calc_cable_size/ via python manage.py generate_help_examples --tool fe_calc_cable_size, which writes help/_load_cable_sizing_corpus_examples.html (checked by calcs/test_help_examples.py).

How to extend:

Add new load types by extending the load_type enum in PARAMETER_SCHEMA in component.py. Load type is currently informational only (does not affect calculations).
Add load-type-specific design factors by modifying check_current_capacity_with_webcalcs_load() to apply different defaults based on the load type.
Extend PVC/EPR support by adding base current tables for Check 1 CCC (currently relies on webcalcs API for all material/insulation combinations).
Add singlecore arrangement reactance tables for trefoil/flat configurations.
Write tests covering both input modes (power and current), edge cases (zero power factor, maximum length, boundary derating), and verify all seven checks independently.