CB Overload Protection — help

Overview

The CB Overload Protection Coordination calculator verifies that a circuit breaker and cable combination satisfies the two overload protection conditions specified in AS/NZS 3000 Clause 2.5.3 (IEC 60364-4-43 Clause 433.1). This ensures that cables are protected from sustained overloads that could cause thermal damage to insulation.

The calculator provides:

Two-condition coordination check — verifies both Condition 2.1 and Condition 2.2
Circuit breaker size/setting matrix — shows all valid CB frame size and thermal setting combinations
Cable selection matrix — evaluates all cable sizes against the selected CB
MCB curve recommendation — suggests B, C, or D curve based on load type

Input Parameters

Parameter	Type	Default	Range	Description
`load_current`	Number	45 A	0.1 – 10000	Design current (I_B) — the current for which the circuit is designed
`load_type`	Enum	general	resistive / general / inductive	Determines recommended MCB curve type (B / C / D)
`cb_frame_size`	Number	63 A	6 – 800	Nominal rated current of the circuit breaker frame (I_N)
`thermal_setting`	Number	1.00	0.40 – 1.00	Thermal current setting as a multiplier of the frame size. Effective I_N = frame × setting
`cable_size`	Number	16 mm²	1 – 500	Conductor cross-sectional area. Current ratings per AS/NZS 3008.1
`parallel_cables`	Integer	1	1 – 6	Number of identical cables run in parallel per phase
`derating_factor`	Number	0.87	0.1 – 1.0	Combined derating factor for installation conditions (grouping, temperature, etc.)

Output Results

Output	Symbol	Unit	Description
Effective I_N	I_N^eff	A	CB frame size × thermal setting
Cable Capacity	I_z	A	Base rating × derating factor × parallel cables
Operating Current	I₂	A	1.45 × I_N^eff — conventional operating current for CBs
Maximum I₂	1.45 × I_z	A	Maximum allowable operating current
Condition 2.1	—	PASS / FAIL	I_B ≤ I_N ≤ I_z
Condition 2.2	—	PASS / FAIL	I₂ ≤ 1.45 × I_z
Overall Result	—	PASS / FAIL	Both conditions must pass
Curve Recommendation	—	B / C / D	Recommended MCB curve based on load type

Formulas

Condition 2.1 — Current Coordination

The protective device must be rated at or above the design current, but not exceed the cable capacity:

I_B ≤ I_N ≤ I_z

Where:

I_B = Design current (maximum demand of the circuit)
I_N = Nominal current of the protective device (effective: frame × thermal setting)
I_z = Current-carrying capacity of the conductor (base rating × derating × parallel count)

Condition 2.2 — Operating Current Limit

The conventional operating current must not exceed 1.45 times the cable capacity:

I₂ ≤ 1.45 × I_z

For circuit breakers, I₂ = 1.45 × I_N. Substituting:

1.45 × I_N ≤ 1.45 × I_z  →  I_N ≤ I_z

Note: For circuit breakers, Condition 2.2 simplifies to I_N ≤ I_z, which is already part of Condition 2.1. However, both are checked independently for completeness and to support future extension to fuses (where I₂ ≠ 1.45 × I_N).

Worked Examples

The 8 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_protection; worked examples for every calculation).

#	Case	I_B (A)	I_n (A)	I_z (A)	I₂ / 1.45 I_z (A)	Curve	Result
1	45 A load, 50 A breaker on 25 mm² XLPE	45	50.0	103.53	72.5 / 150.1	C	PASS
2	63 A frame turned down to 0.8 on 16 mm²	45	50.4	62.64	73.1 / 90.8	C	PASS
3	63 A frame at full setting on 16 mm² fails	45	63.0	62.64	91.3 / 90.8	C	FAIL
4	Load above the breaker rating (resistive, B curve)	70	63.0	103.53	91.3 / 150.1	B	FAIL
5	Boundary: Ib equal to In on 10 mm²	50	50.0	51.30	72.5 / 74.4	C	PASS
6	160 A frame at 0.63 on derated 35 mm²	95	100.8	102.90	146.2 / 149.2	C	PASS
7	Heavy derating 0.6 on 35 mm² fails	80	100.0	88.20	145.0 / 127.9	C	FAIL
8	400 A breaker on 2 × 120 mm² in parallel (motor, D curve)	380	400.0	528.00	580.0 / 765.6	D	PASS

Example 1 — 45 A load, 50 A breaker on 25 mm² XLPE

The default 0.87 derating on a 25 mm² XLPE cable leaves ample margin above a 50 A breaker.

Given: Design current I_B = 45 A (general load); 50 A circuit breaker at thermal setting 1; 1 × 25 mm² copper multicore cable, installation derating 0.87.

Device current	I_n = rating × setting = 50 × 1 = 50.00 A
Cable capacity	Tabulated rating for 25 mm² XLPE multicore Cu in air = 119 A; I_z = 119 × 0.87 × 1 = 103.53 A
Operating current	I₂ = 1.45 × I_n = 1.45 × 50.00 = 72.50 A (circuit-breaker conventional tripping current); limit 1.45 × I_z = 1.45 × 103.53 = 150.12 A
Ib ≤ In	Device rated for the design current: I_B vs I_n → 45.00 vs limit 50.00 A PASS
In ≤ Iz	Device no larger than the cable rating: I_n vs I_z → 50.00 vs limit 103.53 A PASS
I2 ≤ 1.45 Iz	Device operates before 1.45 × the cable rating: I₂ vs 1.45 I_z → 72.50 vs limit 150.12 A PASS
MCB curve	General load → type C (AS/NZS 60898.1 instantaneous band 5–10 × I_n = 250.0–500.0 A)
Alternatives	smallest cable with I_z ≥ 50.00 A at this derating: 16 mm²; largest rating × setting with I_B ≤ I_n ≤ 103.53 A on this cable: 100.8 A
Result	3/3 checks pass → PASS; I_B 45 A, I_n 50.0 A, I_z 103.53 A; governing: ib le in
Reference	Hand calculation (AS/NZS 3000 cl 2.5.3 / IEC 60364-4-43 cl 433.1): In = 50 × 1 = 50 A; Iz = 119 A (component table, 25 mm²) × 0.87 × 1 = 103.53 A; Ib 45 ≤ In 50; In 50 ≤ Iz 103.53; I2 = 1.45 × 50 = 72.50 A ≤ 1.45 Iz = 150.12 A; curve C (AS/NZS 60898.1 instantaneous 250–500 A); smallest table size with Iz ≥ 50 A is 16 mm² (validation case `c0033-45a-50a-25mm2-passes`)

Example 2 — 63 A frame turned down to 0.8 on 16 mm²

An adjustable thermal setting (63 × 0.8 = 50.4 A) brings the breaker inside a 16 mm² cable's rating.

Given: Design current I_B = 45 A (general load); 63 A circuit breaker at thermal setting 0.8; 1 × 16 mm² copper multicore cable, installation derating 0.87.

Device current	I_n = rating × setting = 63 × 0.8 = 50.40 A
Cable capacity	Tabulated rating for 16 mm² PVC multicore Cu in air = 72 A; I_z = 72 × 0.87 × 1 = 62.64 A
Operating current	I₂ = 1.45 × I_n = 1.45 × 50.40 = 73.08 A (circuit-breaker conventional tripping current); limit 1.45 × I_z = 1.45 × 62.64 = 90.83 A
Ib ≤ In	Device rated for the design current: I_B vs I_n → 45.00 vs limit 50.40 A PASS
In ≤ Iz	Device no larger than the cable rating: I_n vs I_z → 50.40 vs limit 62.64 A PASS
I2 ≤ 1.45 Iz	Device operates before 1.45 × the cable rating: I₂ vs 1.45 I_z → 73.08 vs limit 90.83 A PASS
MCB curve	General load → type C (AS/NZS 60898.1 instantaneous band 5–10 × I_n = 252.0–504.0 A)
Alternatives	smallest cable with I_z ≥ 50.40 A at this derating: 16 mm²; largest rating × setting with I_B ≤ I_n ≤ 62.64 A on this cable: 62.5 A
Result	3/3 checks pass → PASS; I_B 45 A, I_n 50.4 A, I_z 62.64 A; governing: ib le in
Reference	Hand calculation (AS/NZS 3000 cl 2.5.3 / IEC 60364-4-43 cl 433.1): In = 63 × 0.8 = 50.4 A; Iz = 72 A (component table, 16 mm²) × 0.87 × 1 = 62.64 A; Ib 45 ≤ In 50.4; In 50.4 ≤ Iz 62.64; I2 = 1.45 × 50.4 = 73.08 A ≤ 1.45 Iz = 90.83 A; curve C (AS/NZS 60898.1 instantaneous 252–504 A); smallest table size with Iz ≥ 50.4 A is 16 mm² (validation case `c0033-63a-setting-0-8-16mm2-passes`)

Example 3 — 63 A frame at full setting on 16 mm² fails

The same circuit with the setting left at 1.0: In = 63 A exceeds Iz = 62.64 A, so both In ≤ Iz and I2 ≤ 1.45 Iz fail.

Given: Design current I_B = 45 A (general load); 63 A circuit breaker at thermal setting 1; 1 × 16 mm² copper multicore cable, installation derating 0.87.

Device current	I_n = rating × setting = 63 × 1 = 63.00 A
Cable capacity	Tabulated rating for 16 mm² PVC multicore Cu in air = 72 A; I_z = 72 × 0.87 × 1 = 62.64 A
Operating current	I₂ = 1.45 × I_n = 1.45 × 63.00 = 91.35 A (circuit-breaker conventional tripping current); limit 1.45 × I_z = 1.45 × 62.64 = 90.83 A
Ib ≤ In	Device rated for the design current: I_B vs I_n → 45.00 vs limit 63.00 A PASS
In ≤ Iz	Device no larger than the cable rating: I_n vs I_z → 63.00 vs limit 62.64 A FAIL
I2 ≤ 1.45 Iz	Device operates before 1.45 × the cable rating: I₂ vs 1.45 I_z → 91.35 vs limit 90.83 A FAIL
MCB curve	General load → type C (AS/NZS 60898.1 instantaneous band 5–10 × I_n = 315.0–630.0 A)
Alternatives	smallest cable with I_z ≥ 63.00 A at this derating: 25 mm²; largest rating × setting with I_B ≤ I_n ≤ 62.64 A on this cable: 62.5 A
Result	1/3 checks pass → FAIL; I_B 45 A, I_n 63.0 A, I_z 62.64 A; governing: in le iz. Reduce circuit breaker setting or increase cable size. The circuit breaker operating current exceeds cable protection limit. Consider a larger cable or smaller breaker.
Reference	Hand calculation (AS/NZS 3000 cl 2.5.3 / IEC 60364-4-43 cl 433.1): In = 63 × 1 = 63 A; Iz = 72 A (component table, 16 mm²) × 0.87 × 1 = 62.64 A; Ib 45 ≤ In 63; In 63 > Iz 62.64; I2 = 1.45 × 63 = 91.35 A > 1.45 Iz = 90.83 A; curve C (AS/NZS 60898.1 instantaneous 315–630 A); smallest table size with Iz ≥ 63 A is 25 mm² (validation case `c0033-45a-63a-16mm2-fails`)

Example 4 — Load above the breaker rating (resistive, B curve)

A 70 A heating load on a 63 A breaker fails Ib ≤ In even though the 25 mm² cable is ample; B-curve band for resistive load.

Given: Design current I_B = 70 A (resistive load); 63 A circuit breaker at thermal setting 1; 1 × 25 mm² copper multicore cable, installation derating 0.87.

Device current	I_n = rating × setting = 63 × 1 = 63.00 A
Cable capacity	Tabulated rating for 25 mm² XLPE multicore Cu in air = 119 A; I_z = 119 × 0.87 × 1 = 103.53 A
Operating current	I₂ = 1.45 × I_n = 1.45 × 63.00 = 91.35 A (circuit-breaker conventional tripping current); limit 1.45 × I_z = 1.45 × 103.53 = 150.12 A
Ib ≤ In	Device rated for the design current: I_B vs I_n → 70.00 vs limit 63.00 A FAIL
In ≤ Iz	Device no larger than the cable rating: I_n vs I_z → 63.00 vs limit 103.53 A PASS
I2 ≤ 1.45 Iz	Device operates before 1.45 × the cable rating: I₂ vs 1.45 I_z → 91.35 vs limit 150.12 A PASS
MCB curve	Resistive load → type B (AS/NZS 60898.1 instantaneous band 3–5 × I_n = 189.0–315.0 A)
Alternatives	largest rating × setting with I_B ≤ I_n ≤ 103.53 A on this cable: 100.8 A
Result	2/3 checks pass → FAIL; I_B 70 A, I_n 63.0 A, I_z 103.53 A; governing: ib le in. Increase circuit breaker rating to cover load current.
Reference	Hand calculation (AS/NZS 3000 cl 2.5.3 / IEC 60364-4-43 cl 433.1): In = 63 × 1 = 63 A; Iz = 119 A (component table, 25 mm²) × 0.87 × 1 = 103.53 A; Ib 70 > In 63; In 63 ≤ Iz 103.53; I2 = 1.45 × 63 = 91.35 A ≤ 1.45 Iz = 150.12 A; curve B (AS/NZS 60898.1 instantaneous 189–315 A) (validation case `c0033-load-exceeds-breaker-fails`)

Example 5 — Boundary: Ib equal to In on 10 mm²

Ib = In = 50 A is allowed (≤), and Iz = 54 × 0.95 = 51.3 A just covers In: a pass at 100 % utilisation.

Given: Design current I_B = 50 A (general load); 50 A circuit breaker at thermal setting 1; 1 × 10 mm² copper multicore cable, installation derating 0.95.

Device current	I_n = rating × setting = 50 × 1 = 50.00 A
Cable capacity	Tabulated rating for 10 mm² PVC multicore Cu in air = 54 A; I_z = 54 × 0.95 × 1 = 51.30 A
Operating current	I₂ = 1.45 × I_n = 1.45 × 50.00 = 72.50 A (circuit-breaker conventional tripping current); limit 1.45 × I_z = 1.45 × 51.30 = 74.38 A
Ib ≤ In	Device rated for the design current: I_B vs I_n → 50.00 vs limit 50.00 A PASS
In ≤ Iz	Device no larger than the cable rating: I_n vs I_z → 50.00 vs limit 51.30 A PASS
I2 ≤ 1.45 Iz	Device operates before 1.45 × the cable rating: I₂ vs 1.45 I_z → 72.50 vs limit 74.38 A PASS
MCB curve	General load → type C (AS/NZS 60898.1 instantaneous band 5–10 × I_n = 250.0–500.0 A)
Alternatives	smallest cable with I_z ≥ 50.00 A at this derating: 10 mm²; largest rating × setting with I_B ≤ I_n ≤ 51.30 A on this cable: 50.4 A
Result	3/3 checks pass → PASS; I_B 50 A, I_n 50.0 A, I_z 51.30 A; governing: ib le in
Reference	Hand calculation (AS/NZS 3000 cl 2.5.3 / IEC 60364-4-43 cl 433.1): In = 50 × 1 = 50 A; Iz = 54 A (component table, 10 mm²) × 0.95 × 1 = 51.30 A; Ib 50 ≤ In 50; In 50 ≤ Iz 51.30; I2 = 1.45 × 50 = 72.50 A ≤ 1.45 Iz = 74.38 A; curve C (AS/NZS 60898.1 instantaneous 250–500 A); smallest table size with Iz ≥ 50 A is 10 mm² (validation case `c0033-boundary-ib-equals-in`)

Example 6 — 160 A frame at 0.63 on derated 35 mm²

A 0.63 thermal setting (100.8 A) on a heavily derated (0.7) 35 mm² XLPE cable passes with 2 A to spare.

Given: Design current I_B = 95 A (general load); 160 A circuit breaker at thermal setting 0.63; 1 × 35 mm² copper multicore cable, installation derating 0.7.

Device current	I_n = rating × setting = 160 × 0.63 = 100.80 A
Cable capacity	Tabulated rating for 35 mm² XLPE multicore Cu in air = 147 A; I_z = 147 × 0.7 × 1 = 102.90 A
Operating current	I₂ = 1.45 × I_n = 1.45 × 100.80 = 146.16 A (circuit-breaker conventional tripping current); limit 1.45 × I_z = 1.45 × 102.90 = 149.20 A
Ib ≤ In	Device rated for the design current: I_B vs I_n → 95.00 vs limit 100.80 A PASS
In ≤ Iz	Device no larger than the cable rating: I_n vs I_z → 100.80 vs limit 102.90 A PASS
I2 ≤ 1.45 Iz	Device operates before 1.45 × the cable rating: I₂ vs 1.45 I_z → 146.16 vs limit 149.20 A PASS
MCB curve	General load → type C (AS/NZS 60898.1 instantaneous band 5–10 × I_n = 504.0–1,008.0 A)
Alternatives	smallest cable with I_z ≥ 100.80 A at this derating: 35 mm²; largest rating × setting with I_B ≤ I_n ≤ 102.90 A on this cable: 100.8 A
Result	3/3 checks pass → PASS; I_B 95 A, I_n 100.8 A, I_z 102.90 A; governing: in le iz
Reference	Hand calculation (AS/NZS 3000 cl 2.5.3 / IEC 60364-4-43 cl 433.1): In = 160 × 0.63 = 100.8 A; Iz = 147 A (component table, 35 mm²) × 0.7 × 1 = 102.90 A; Ib 95 ≤ In 100.8; In 100.8 ≤ Iz 102.90; I2 = 1.45 × 100.8 = 146.16 A ≤ 1.45 Iz = 149.20 A; curve C (AS/NZS 60898.1 instantaneous 504–1008 A); smallest table size with Iz ≥ 100.8 A is 35 mm² (validation case `c0033-160a-setting-0-63-35mm2`)

Example 7 — Heavy derating 0.6 on 35 mm² fails

With a 0.6 grouping/ambient derating 35 mm² carries only 88.2 A under a 100 A breaker; the tool reports 50 mm² as the smallest passing cable and 87.5 A as the largest passing setting.

Given: Design current I_B = 80 A (general load); 100 A circuit breaker at thermal setting 1; 1 × 35 mm² copper multicore cable, installation derating 0.6.

Device current	I_n = rating × setting = 100 × 1 = 100.00 A
Cable capacity	Tabulated rating for 35 mm² XLPE multicore Cu in air = 147 A; I_z = 147 × 0.6 × 1 = 88.20 A
Operating current	I₂ = 1.45 × I_n = 1.45 × 100.00 = 145.00 A (circuit-breaker conventional tripping current); limit 1.45 × I_z = 1.45 × 88.20 = 127.89 A
Ib ≤ In	Device rated for the design current: I_B vs I_n → 80.00 vs limit 100.00 A PASS
In ≤ Iz	Device no larger than the cable rating: I_n vs I_z → 100.00 vs limit 88.20 A FAIL
I2 ≤ 1.45 Iz	Device operates before 1.45 × the cable rating: I₂ vs 1.45 I_z → 145.00 vs limit 127.89 A FAIL
MCB curve	General load → type C (AS/NZS 60898.1 instantaneous band 5–10 × I_n = 500.0–1,000.0 A)
Alternatives	smallest cable with I_z ≥ 100.00 A at this derating: 50 mm²; largest rating × setting with I_B ≤ I_n ≤ 88.20 A on this cable: 87.5 A
Result	1/3 checks pass → FAIL; I_B 80 A, I_n 100.0 A, I_z 88.20 A; governing: in le iz. Reduce circuit breaker setting or increase cable size. The circuit breaker operating current exceeds cable protection limit. Consider a larger cable or smaller breaker.
Reference	Hand calculation (AS/NZS 3000 cl 2.5.3 / IEC 60364-4-43 cl 433.1): In = 100 × 1 = 100 A; Iz = 147 A (component table, 35 mm²) × 0.6 × 1 = 88.20 A; Ib 80 ≤ In 100; In 100 > Iz 88.20; I2 = 1.45 × 100 = 145.00 A > 1.45 Iz = 127.89 A; curve C (AS/NZS 60898.1 instantaneous 500–1000 A); smallest table size with Iz ≥ 100 A is 50 mm²; largest frame × setting with 80 ≤ In ≤ 88.2 A is 125 × 0.7 = 87.5 A (validation case `c0033-heavy-derating-fails-50mm2-needed`)

Example 8 — 400 A breaker on 2 × 120 mm² in parallel (motor, D curve)

Two parallel 120 mm² XLPE cables at 0.8 derating give Iz = 528 A for a 380 A motor load on a 400 A breaker; D curve for inrush.

Given: Design current I_B = 380 A (inductive load); 400 A circuit breaker at thermal setting 1; 2 × 120 mm² copper multicore cables in parallel, installation derating 0.8.

Device current	I_n = rating × setting = 400 × 1 = 400.00 A
Cable capacity	Tabulated rating for 120 mm² XLPE multicore Cu in air = 330 A; I_z = 330 × 0.8 × 2 = 528.00 A
Operating current	I₂ = 1.45 × I_n = 1.45 × 400.00 = 580.00 A (circuit-breaker conventional tripping current); limit 1.45 × I_z = 1.45 × 528.00 = 765.60 A
Ib ≤ In	Device rated for the design current: I_B vs I_n → 380.00 vs limit 400.00 A PASS
In ≤ Iz	Device no larger than the cable rating: I_n vs I_z → 400.00 vs limit 528.00 A PASS
I2 ≤ 1.45 Iz	Device operates before 1.45 × the cable rating: I₂ vs 1.45 I_z → 580.00 vs limit 765.60 A PASS
MCB curve	Inductive load → type D (AS/NZS 60898.1 instantaneous band 10–20 × I_n = 4,000.0–8,000.0 A)
Alternatives	smallest cable with I_z ≥ 400.00 A at this derating: 95 mm²; largest rating × setting with I_B ≤ I_n ≤ 528.00 A on this cable: 504.0 A
Result	3/3 checks pass → PASS; I_B 380 A, I_n 400.0 A, I_z 528.00 A; governing: ib le in
Reference	Hand calculation (AS/NZS 3000 cl 2.5.3 / IEC 60364-4-43 cl 433.1): In = 400 × 1 = 400 A; Iz = 330 A (component table, 120 mm²) × 0.8 × 2 = 528.00 A; Ib 380 ≤ In 400; In 400 ≤ Iz 528.00; I2 = 1.45 × 400 = 580.00 A ≤ 1.45 Iz = 765.60 A; curve D (AS/NZS 60898.1 instantaneous 4000–8000 A); smallest table size with Iz ≥ 400 A is 95 mm² (validation case `c0033-parallel-2x120mm2-400a`)

Standards & References

AS/NZS 3000:2018 — Electrical installations (Wiring Rules). Clause 2.5.3 sets the coordination conditions between conductors and overload protective devices.
AS/NZS 3008.1:2017 — Electrical installations – Selection of cables. Source of the current-carrying capacities (I_z).
IEC 60364-4-43 — Protection against overcurrent. International equivalent of the AS/NZS coordination requirements.
AS/NZS 60898.1 — Circuit breakers for overcurrent protection. Defines B, C, and D curve characteristics.

Tips & Limitations

The derating factor should account for all installation derating: ambient temperature, grouping, burial depth, soil resistivity, etc. Use the Motor/Load Cable Sizing calculator for precise derating calculations.
Cable ratings are for 3-phase multicore copper conductors in air. PVC insulation is used for sizes up to 16mm²; XLPE for 25mm² and above.
The I₂ = 1.45 × I_N relationship applies specifically to circuit breakers. For HRC fuses, I₂ varies — this calculator does not cover fuse coordination.
Parallel cables multiply the total cable capacity. Ensure all parallel cables are identical (same size, type, length, and installation method).
The CB matrix highlights all valid frame/setting combinations for the selected cable — useful for exploring alternatives without re-running the calculation.

Developer Guide — Architecture

This calculator follows the standard calcs component pattern:

components/c0033_cb_overload_protection/
├── __init__.py              # Docstring
├── apps.py                  # Django AppConfig
├── calculations.py          # Pure Python — all math, no Django
├── component.py             # Schema, Calculator class, builders, registration
├── equations.py             # LaTeX equation templates
└── templates/.../sidebar_form.html  # Vue 3 sidebar form

Data flow: Sidebar form → CBOverloadProtectionCalculator.calculate() → calculate_cb_overload_protection() (pure Python) → results dict → equation_builder() / summary_cards_builder() → UI rendering

Developer Guide — Code Paths

Purpose	File	Key Function / Class
Core evaluation	`calculations.py`	`evaluate_coordination(ib, in_effective, iz)`
CB matrix	`calculations.py`	`build_cb_matrix(ib, iz)`
Cable matrix	`calculations.py`	`build_cable_matrix(ib, in_effective, derating, parallel)`
Main entry	`calculations.py`	`calculate_cb_overload_protection(data)`
Validation	`component.py`	`CBOverloadProtectionCalculator.validate_parameters()`
Registration	`component.py`	`register_component(registry)`
Excel export	`excel_generator.py`	`create_c0033_excel_report(calculation)`

Developer Guide — Testing

# Run all tests for this component
pytest calcs/test_c0033_cb_overload_protection.py -v

Test coverage includes:

TestEvaluateCoordination — safe/unsafe combinations, boundary cases
TestGetCableRating — valid/invalid size lookups
TestGetCurveRecommendation — B/C/D curve mapping
TestBuildCBMatrix — matrix structure, known safe/unsafe entries
TestBuildCableMatrix — all sizes, parallel cable multiplier
TestCalculateCBOverloadProtection — full integration, pass/fail, recommendations
TestCalculatorClass — validation, round-trip through calculator