Generator Sizing Calculator — help

Overview

Calculates the required generator capacity for industrial and commercial facilities based on connected loads, diversity factors, motor starting characteristics, and fuel autonomy requirements. The calculator determines the sizing basis (running load or motor starting demand), applies a safety margin, and selects the next standard generator size. Supports parallel generator configurations and provides optimisation recommendations such as soft starter installation.

Input Parameters

Facility Parameters

Parameter	Type	Default	Range	Description
`facility_type`	Enum	manufacturing	—	Type of facility — determines the diversity factor. Options: continuous_process, manufacturing, commercial, accommodation, essential_services
`custom_diversity`	Number	none	0.5 – 1.0	Override the automatic diversity factor with a custom value
`safety_margin`	Number	1.25	1.0 – 2.0	Safety margin applied to required kVA before selecting standard size (1.25 = 25%)

Connected Loads (array)

Each entry in the loads array represents a connected load or group of identical loads. At least one load is required.

Parameter	Type	Default	Range	Description
`name`	String	required	—	Descriptive name for the load
`power_kw`	Number	required	min 0	Power rating in kW (per unit)
`quantity`	Integer	1	min 1	Number of identical loads
`load_type`	Enum	motor	—	Load type: motor, resistive, welding, hvac, pumps, lighting, control
`power_factor`	Number	auto	0.5 – 1.0	Power factor (if omitted, a typical value is used based on load_type)
`duty_cycle`	Number	1.0	0.1 – 1.0	Duty cycle factor for intermittent loads
`starting_method`	Enum	dol	—	Motor starting method: dol, star_delta, soft_start, vsd (applies to the motor-driven load types motor, pumps and hvac)

Analysis Options

Parameter	Type	Default	Range	Description
`include_starting_analysis`	Boolean	True	—	Include motor starting demand in sizing analysis
`fuel_tank_capacity`	Number	none	min 0	Fuel tank capacity in litres — enables autonomy calculation
`consider_parallel`	Boolean	False	—	Evaluate a parallel generator configuration
`num_parallel_generators`	Integer	2	2 – 4	Number of parallel units (hidden when consider_parallel is false)

Output Results

Primary Results

Output	Unit	Description
`selected_generator_kva`	kVA	Recommended standard generator size
`required_kva`	kVA	Required capacity before rounding to standard size
`sizing_basis`	text	"running" or "starting" — which demand drove the selection
`generator_utilization`	%	Utilization of the selected generator at diversified running load
`fuel_consumption_l_per_hour`	L/hr	Estimated diesel fuel consumption at operating load
`fuel_autonomy_hours`	hr	Hours of operation on the specified fuel tank (only if fuel_tank_capacity is provided)

Running Load Analysis

Output	Unit	Description
`running_load.total_kva`	kVA	Total connected load (before diversity)
`running_load.diversified_kva`	kVA	Diversified running load
`running_load.diversity_factor`	—	Applied diversity factor
`running_load.overall_pf`	—	Overall power factor of connected loads

Starting Load Analysis

Output	Unit	Description
`starting_load.largest_starting_kva`	kVA	Starting kVA of the largest motor
`starting_load.background_kva`	kVA	kVA of other loads running during motor start
`starting_load.total_starting_demand`	kVA	Total demand during motor starting event

Parallel Generator Analysis

Output	Unit	Description
`parallel_generators.size_per_unit_kva`	kVA	Selected standard size per generator unit
`parallel_generators.total_capacity_kva`	kVA	Combined capacity of all parallel units
`parallel_generators.redundancy_percent`	%	Redundancy above required capacity
`parallel_generators.n_plus_1_capable`	Boolean	Whether the configuration can lose one unit and still meet demand

Formulas

Load kVA from kW

\[ S_{load} = \frac{P_{kW} \times D}{\cos\phi} \quad (\text{kVA}) \]

Where \(P_{kW}\) is the rated power, \(D\) is the duty cycle (0.1–1.0), and \(\cos\phi\) is the power factor.

Motor Starting kVA

\[ S_{start} = P_{kW} \times k_{start} \quad (\text{kVA}) \]

Where \(k_{start}\) is the starting multiplier for the chosen starting method. Every motor-driven load is a starting candidate: load types motor, pumps and hvac (pump, compressor and fan motors). \(P_{kW}\) is the rating of one unit — quantity and duty cycle do not change the starting kVA.

Starting Multipliers

Starting Method	\(k_{start}\)	Notes
Direct-On-Line (DOL)	6.0	Full voltage start — highest starting demand
Star-Delta	2.0	Reduced voltage start (1/3 of DOL current)
Soft Start	2.5	Controlled ramp-up via thyristors
VSD	1.2	Variable Speed Drive — minimal starting impact

Diversified Running Load

\[ S_{diversified} = S_{total} \times f_{diversity} \quad (\text{kVA}) \]

Where \(S_{total} = \sum (S_{load,i} \times n_i)\) is the sum of all individual load kVA values multiplied by quantity, and \(f_{diversity}\) is the diversity factor for the facility type.

Diversity Factors by Facility Type

Facility Type	\(f_{diversity}\)
Continuous Process	0.95
Manufacturing	0.75
Commercial	0.80
Accommodation	0.85
Essential Services	1.00

Total Starting Demand

\[ S_{starting\_demand} = S_{start,largest} + S_{diversified} \quad (\text{kVA}) \]

The worst-case starting event is the motor-driven load (motor, pumps or hvac) with the largest \(S_{start}\) starting while all loads are running at the diversified level.

Sizing Basis

\[ S_{required} = \max\!\left(S_{diversified},\; S_{starting\_demand}\right) \]

The generator is sized for whichever demand is greater: the diversified running load or the total starting demand.

Generator Selection

\[ S_{selected} = \text{next standard size} \geq S_{required} \times m_{safety} \]

Where \(m_{safety}\) is the safety margin (default 1.25). The selected size is the smallest value from the standard sizes list that meets or exceeds the required capacity with margin.

Generator Utilization

\[ U = \frac{S_{required}}{S_{selected}} \times 100 \quad (\%) \]

Fuel Consumption

\[ \dot{F} = S_{selected} \times 0.8 \times f_{load} \times 0.25 \quad (\text{L/hr}) \]

Where \(f_{load} = S_{diversified} / S_{selected}\) is the operating load factor. The 0.8 factor converts kVA to approximate kW, and 0.25 L/kWh is a typical diesel consumption rate.

Fuel Autonomy

\[ t_{autonomy} = \frac{V_{tank}}{\dot{F}} \quad (\text{hours}) \]

Where \(V_{tank}\) is the fuel tank capacity in litres and \(\dot{F}\) is the hourly fuel consumption.

Typical Power Factors

Load Type	\(\cos\phi\)
Motor	0.87
Resistive	1.00
Welding	0.70
HVAC	0.88
Pumps	0.88
Lighting	0.95
Control	1.00

Standard Generator Sizes (kVA)

Available Sizes
100, 125, 150, 175, 200, 250, 300, 350, 400, 450, 500, 600, 750, 800, 900, 1000, 1250, 1500, 1750, 2000, 2250, 2500, 3000, 3500, 4000, 5000

Worked Examples

The 21 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_generator; worked examples for every calculation).

#	Case	Running (kVA)	Starting (kVA)	Basis	Selected (kVA)	Result
1	100 kW resistive load in a commercial building	80.00	80.00	running	100	PASS
2	75 kW DOL pump with lighting, two units in parallel	109.29	559.29	starting	750	FAIL
3	Remote accommodation camp with 5000 L tank	144.12	234.12	starting	300	PASS
4	4500 kW furnace beyond the standard ratings	4,500.00	–	running	5,700	PASS
5	Press shop with a 0.6 diversity override	85.74	415.74	starting	600	PASS
6	Large DOL pump (load type pumps) sets the starting demand	327.76	1,119.76	starting	1,500	PASS
7	4000 kW electric boilers on the largest standard rating	4,000.00	–	running	5,000	PASS
8	Manufacturing workshop with VSD machines and welding	88.99	151.49	starting	200	PASS
9	400 kW heater bank with no safety margin	400.00	–	running	400	PASS
10	Hospital standby set with a 1.5 safety margin	205.27	655.27	starting	1,000	PASS
11	Eight 22 kW motors with motor starting excluded	189.23	–	running	250	PASS
12	Cold store with three DOL compressors on four units	505.80	1,165.80	starting	1,500	FAIL
13	Four parallel units with a soft-started crusher	510.00	735.00	starting	1,000	PASS
14	Three parallel units carrying the load with one out	80.00	200.00	starting	250	PASS
15	500 kVA essential load on two parallel units	500.00	–	running	750	FAIL
16	Small shop on two 100 kVA units, no motors	80.00	80.00	running	100	PASS
17	Smaller DOL agitator out-starts a larger star-delta mixer	175.95	445.95	starting	600	PASS
18	160 kW soft-started borehole pump	193.61	593.61	starting	750	PASS
19	132 kW star-delta compressor governs starting	143.76	407.76	starting	600	PASS
20	Water pumping station (continuous process)	149.57	809.57	starting	1,250	PASS
21	Welding shop with 50 % duty welders and pump loads	80.62	170.62	starting	250	PASS

Example 1 — 100 kW resistive load in a commercial building

A purely resistive load with commercial diversity lands exactly on the 100 kVA rating, sized on the running load.

Given: Loads: Heaters 100 kW (resistive, typical pf). Commercial facility (typical diversity); safety margin 1.25, largest-motor starting checked.

Load kVA	S_load = P × duty / pf × qty: Heaters: 100 / 1 = 100.00 kVA
Connected	S_total = 100.00 = 100.00 kVA; P_total = 100.00 kW; overall pf = 100.00 / 100.00 = 1.000
Running load	S_div = 100.00 × 0.8 (commercial) = 80.00 kVA (80.00 kW)
Starting demand	No motor-driven loads (motor, pumps, hvac) → S_sd = 0 + 80.00 = 80.00 kVA
Sizing	S_req = max(80.00, 80.00) = 80.00 kVA → sized on running; S_req × m = 80.00 × 1.25 = 100.00 kVA → next standard rating ≥ 100.00 = 100 kVA PASS
Utilisation	Running = 80.00 / 100 = 80.0 %; peak = 80.00 / 100 = 80.0 %
Fuel	F = 100 × 0.8 × (80.00 / 100) × 0.25 = 16.00 L/h
Result	1/1 checks pass → PASS; 100 kVA set, running utilisation 80.0 %; governing: running load
Reference	Hand calculation: S = 100/1 = 100.00 kVA; running = 100.00 × 0.8 = 80.00 kVA; no motor loads, so starting demand = running load; 80.00 × 1.25 = 100.00 → 100 kVA (running); running utilisation = 80.00/100 = 80.0 %; fuel = 0.25 × 100 × 0.8 × 80.00/100 = 16.00 L/h (validation case `c0014-100kw-resistive-commercial`)

Example 2 — 75 kW DOL pump with lighting, two units in parallel

A DOL-started pump drives the rating on starting demand; a 2-unit parallel set cannot carry the starting load with one unit out, and the tank gives the autonomy.

Given: Loads: Pump 75 kW (motor, pf 0.85, DOL starting); Lights 20 kW (lighting, typical pf). Essential services facility (typical diversity); safety margin 1.25, largest-motor starting checked, fuel tank 1,000 L, 2 identical units in parallel.

Load kVA	S_load = P × duty / pf × qty: Pump: 75 / 0.85 = 88.24 kVA; Lights: 20 / 0.95 = 21.05 kVA
Connected	S_total = 88.24 + 21.05 = 109.29 kVA; P_total = 95.00 kW; overall pf = 95.00 / 109.29 = 0.869
Running load	S_div = 109.29 × 1 (essential services) = 109.29 kVA (95.00 kW)
Starting demand	Largest starting kVA: Pump 75 kW DOL → S_start = 6 × 75 = 450.00 kVA; S_sd = 450.00 + 109.29 = 559.29 kVA
Sizing	S_req = max(109.29, 559.29) = 559.29 kVA → sized on starting; S_req × m = 559.29 × 1.25 = 699.11 kVA → next standard rating ≥ 699.11 = 750 kVA PASS
Utilisation	Running = 109.29 / 750 = 14.6 %; peak = 559.29 / 750 = 74.6 %
Fuel	F = 750 × 0.8 × (109.29 / 750) × 0.25 = 21.86 L/h; autonomy = 1,000 / 21.86 = 45.7 h
Parallel set	Unit = next standard ≥ 1.1 × 559.29 / 2 = 307.61 → 350 kVA; 2 × 350 = 700 kVA; N−1 = 1 × 350 = 350 kVA vs S_req 559.29 kVA (159.8 %) FAIL
Result	1/2 checks pass → FAIL; 750 kVA set, running utilisation 14.6 %; governing: motor starting. Install soft starter on Pump: Reduce generator from 750 kVA to 400 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 75/0.85 + 20/0.95 = 109.29 kVA; running = 109.29 × 1 = 109.29 kVA; start = 6 × 75 + 109.29 = 559.29 kVA; 559.29 × 1.25 = 699.11 → 750 kVA (starting); running utilisation = 109.29/750 = 14.6 %; peak = 559.29/750 = 74.6 %; fuel = 0.25 × 750 × 0.8 × 109.29/750 = 21.86 L/h; autonomy = 1000/21.86 = 45.7 h; parallel 2 units: 1.1 × 559.29/2 = 307.61 → 350 kVA each, N−1 = 350 kVA < 559.29 kVA (validation case `c0014-75kw-dol-pump-with-lighting`)

Example 3 — Remote accommodation camp with 5000 L tank

Mixed HVAC, lighting, kitchen, control and a soft-started pump at accommodation diversity, with the typical power factor of each load type and the tank autonomy; the DOL split AC units (hvac is motor-driven) set the starting demand, not the soft-started pump.

Given: Loads: Split AC units 15 kW × 6 (hvac, typical pf, DOL starting); Lighting 12 kW (lighting, typical pf); Kitchen 40 kW (resistive, typical pf); Water pump 11 kW (motor, typical pf, soft-start starting); Control 2 kW (control, typical pf). Accommodation facility (typical diversity); safety margin 1.25, largest-motor starting checked, fuel tank 5,000 L.

Load kVA	S_load = P × duty / pf × qty: Split AC units: 15 / 0.88 × 6 = 102.27 kVA; Lighting: 12 / 0.95 = 12.63 kVA; Kitchen: 40 / 1 = 40.00 kVA; Water pump: 11 / 0.87 = 12.64 kVA; Control: 2 / 1 = 2.00 kVA
Connected	S_total = 102.27 + 12.63 + 40.00 + 12.64 + 2.00 = 169.55 kVA; P_total = 155.00 kW; overall pf = 155.00 / 169.55 = 0.914
Running load	S_div = 169.55 × 0.85 (accommodation) = 144.12 kVA (131.75 kW)
Starting demand	Largest starting kVA: Split AC units 15 kW DOL → S_start = 6 × 15 = 90.00 kVA; S_sd = 90.00 + 144.12 = 234.12 kVA
Sizing	S_req = max(144.12, 234.12) = 234.12 kVA → sized on starting; S_req × m = 234.12 × 1.25 = 292.65 kVA → next standard rating ≥ 292.65 = 300 kVA PASS
Utilisation	Running = 144.12 / 300 = 48.0 %; peak = 234.12 / 300 = 78.0 %
Fuel	F = 300 × 0.8 × (144.12 / 300) × 0.25 = 28.82 L/h; autonomy = 5,000 / 28.82 = 173.5 h
Result	1/1 checks pass → PASS; 300 kVA set, running utilisation 48.0 %; governing: motor starting. Install soft starter on Split AC units: Reduce generator from 300 kVA to 250 kVA
Reference	Hand calculation: S = 15/0.88 × 6 + 12/0.95 + 40/1 + 11/0.87 + 2/1 = 169.55 kVA; running = 169.55 × 0.85 = 144.12 kVA; start = 6 × 15 (Split AC units, hvac) + 144.12 = 234.12 kVA; 234.12 × 1.25 = 292.65 → 300 kVA (starting); running utilisation = 144.12/300 = 48.0 %; peak = 234.12/300 = 78.0 %; fuel = 0.25 × 300 × 0.8 × 144.12/300 = 28.82 L/h; autonomy = 5000/28.82 = 173.5 h (validation case `c0014-accommodation-camp`)

Example 4 — 4500 kW furnace beyond the standard ratings

Above 5000 kVA the tool rounds up to the next 100 kVA (5625 → 5700 kVA) instead of a list entry.

Given: Loads: Arc furnace supply 4,500 kW (resistive, typical pf). Essential services facility (typical diversity); safety margin 1.25, motor starting not checked.

Load kVA	S_load = P × duty / pf × qty: Arc furnace supply: 4,500 / 1 = 4,500.00 kVA
Connected	S_total = 4,500.00 = 4,500.00 kVA; P_total = 4,500.00 kW; overall pf = 4,500.00 / 4,500.00 = 1.000
Running load	S_div = 4,500.00 × 1 (essential services) = 4,500.00 kVA (4,500.00 kW)
Starting demand	Motor starting not checked (include_motor_starting = no)
Sizing	S_req = S_div = 4,500.00 kVA → sized on running; S_req × m = 4,500.00 × 1.25 = 5,625.00 kVA → above 5000 kVA, next 100 kVA ≥ 5,625.00 = 5,700 kVA PASS
Utilisation	Running = 4,500.00 / 5,700 = 79.0 %; peak = 4,500.00 / 5,700 = 79.0 %
Fuel	F = 5,700 × 0.8 × (4,500.00 / 5,700) × 0.25 = 900.00 L/h
Result	1/1 checks pass → PASS; 5,700 kVA set, running utilisation 79.0 %; governing: running load
Reference	Hand calculation: S = 4500/1 = 4500.00 kVA; running = 4500.00 × 1 = 4500.00 kVA; 4500.00 × 1.25 = 5625.00 → 5700 kVA (running); running utilisation = 4500.00/5700 = 79.0 %; fuel = 0.25 × 5700 × 0.8 × 4500.00/5700 = 900.00 L/h (validation case `c0014-beyond-standard-ratings`)

Example 5 — Press shop with a 0.6 diversity override

diversity_factor overrides the manufacturing default of 0.75; six lathes and a 40 % duty welder show quantity and duty cycle in the load kVA.

Given: Loads: Press 55 kW (motor, pf 0.86, DOL starting); Lathes 7.5 kW × 6 (motor, typical pf, DOL starting); Lighting 15 kW (lighting, typical pf); Welder 20 kW (welding, typical pf, duty 0.4). Diversity override 0.6; safety margin 1.25, largest-motor starting checked.

Load kVA	S_load = P × duty / pf × qty: Press: 55 / 0.86 = 63.95 kVA; Lathes: 7.5 / 0.87 × 6 = 51.72 kVA; Lighting: 15 / 0.95 = 15.79 kVA; Welder: 20 × 0.4 / 0.7 = 11.43 kVA
Connected	S_total = 63.95 + 51.72 + 15.79 + 11.43 = 142.90 kVA; P_total = 123.00 kW; overall pf = 123.00 / 142.90 = 0.861
Running load	S_div = 142.90 × 0.6 (given) = 85.74 kVA (73.80 kW)
Starting demand	Largest starting kVA: Press 55 kW DOL → S_start = 6 × 55 = 330.00 kVA; S_sd = 330.00 + 85.74 = 415.74 kVA
Sizing	S_req = max(85.74, 415.74) = 415.74 kVA → sized on starting; S_req × m = 415.74 × 1.25 = 519.67 kVA → next standard rating ≥ 519.67 = 600 kVA PASS
Utilisation	Running = 85.74 / 600 = 14.3 %; peak = 415.74 / 600 = 69.3 %
Fuel	F = 600 × 0.8 × (85.74 / 600) × 0.25 = 17.15 L/h
Result	1/1 checks pass → PASS; 600 kVA set, running utilisation 14.3 %; governing: motor starting. Install soft starter on Press: Reduce generator from 600 kVA to 300 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 55/0.86 + 7.5/0.87 × 6 + 15/0.95 + 20 × 0.4/0.7 = 142.90 kVA; running = 142.90 × 0.6 = 85.74 kVA; start = 6 × 55 + 85.74 = 415.74 kVA; 415.74 × 1.25 = 519.67 → 600 kVA (starting); running utilisation = 85.74/600 = 14.3 %; peak = 415.74/600 = 69.3 %; fuel = 0.25 × 600 × 0.8 × 85.74/600 = 17.15 L/h (validation case `c0014-diversity-override`)

Example 6 — Large DOL pump (load type pumps) sets the starting demand

A 132 kW pump entered as load type 'pumps' is a motor-driven starting candidate: its DOL start (6 × 132 kW) outweighs the 30 kW motor and drives the rating; quantity 2 does not double the single-unit starting kVA.

Given: Loads: Raw water pump 132 kW × 2 (pumps, typical pf, DOL starting); Dosing skid 30 kW (motor, typical pf, DOL starting); Lighting 10 kW (lighting, typical pf). Continuous process facility (typical diversity); safety margin 1.25, largest-motor starting checked, fuel tank 3,000 L.

Load kVA	S_load = P × duty / pf × qty: Raw water pump: 132 / 0.88 × 2 = 300.00 kVA; Dosing skid: 30 / 0.87 = 34.48 kVA; Lighting: 10 / 0.95 = 10.53 kVA
Connected	S_total = 300.00 + 34.48 + 10.53 = 345.01 kVA; P_total = 304.00 kW; overall pf = 304.00 / 345.01 = 0.881
Running load	S_div = 345.01 × 0.95 (continuous process) = 327.76 kVA (288.80 kW)
Starting demand	Largest starting kVA: Raw water pump 132 kW DOL → S_start = 6 × 132 = 792.00 kVA; S_sd = 792.00 + 327.76 = 1,119.76 kVA
Sizing	S_req = max(327.76, 1,119.76) = 1,119.76 kVA → sized on starting; S_req × m = 1,119.76 × 1.25 = 1,399.70 kVA → next standard rating ≥ 1,399.70 = 1,500 kVA PASS
Utilisation	Running = 327.76 / 1,500 = 21.9 %; peak = 1,119.76 / 1,500 = 74.7 %
Fuel	F = 1,500 × 0.8 × (327.76 / 1,500) × 0.25 = 65.55 L/h; autonomy = 3,000 / 65.55 = 45.8 h
Result	1/1 checks pass → PASS; 1,500 kVA set, running utilisation 21.9 %; governing: motor starting. Install soft starter on Raw water pump: Reduce generator from 1500 kVA to 900 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 132/0.88 × 2 + 30/0.87 + 10/0.95 = 345.01 kVA; running = 345.01 × 0.95 = 327.76 kVA; start = 6 × 132 (Raw water pump, pumps) + 327.76 = 1119.76 kVA; 1119.76 × 1.25 = 1399.70 → 1500 kVA (starting); running utilisation = 327.76/1500 = 21.9 %; peak = 1119.76/1500 = 74.7 %; fuel = 0.25 × 1500 × 0.8 × 327.76/1500 = 65.55 L/h; autonomy = 3000/65.55 = 45.8 h (validation case `c0014-large-pump-governs-starting`)

Example 7 — 4000 kW electric boilers on the largest standard rating

4000 kVA × 1.25 = 5000 kVA exactly: the largest entry in the standard rating list.

Given: Loads: Electric boiler 2,000 kW × 2 (resistive, typical pf). Essential services facility (typical diversity); safety margin 1.25, motor starting not checked.

Load kVA	S_load = P × duty / pf × qty: Electric boiler: 2,000 / 1 × 2 = 4,000.00 kVA
Connected	S_total = 4,000.00 = 4,000.00 kVA; P_total = 4,000.00 kW; overall pf = 4,000.00 / 4,000.00 = 1.000
Running load	S_div = 4,000.00 × 1 (essential services) = 4,000.00 kVA (4,000.00 kW)
Starting demand	Motor starting not checked (include_motor_starting = no)
Sizing	S_req = S_div = 4,000.00 kVA → sized on running; S_req × m = 4,000.00 × 1.25 = 5,000.00 kVA → next standard rating ≥ 5,000.00 = 5,000 kVA PASS
Utilisation	Running = 4,000.00 / 5,000 = 80.0 %; peak = 4,000.00 / 5,000 = 80.0 %
Fuel	F = 5,000 × 0.8 × (4,000.00 / 5,000) × 0.25 = 800.00 L/h
Result	1/1 checks pass → PASS; 5,000 kVA set, running utilisation 80.0 %; governing: running load
Reference	Hand calculation: S = 2000/1 × 2 = 4000.00 kVA; running = 4000.00 × 1 = 4000.00 kVA; 4000.00 × 1.25 = 5000.00 → 5000 kVA (running); running utilisation = 4000.00/5000 = 80.0 %; fuel = 0.25 × 5000 × 0.8 × 4000.00/5000 = 800.00 L/h (validation case `c0014-largest-standard-rating`)

Example 8 — Manufacturing workshop with VSD machines and welding

Two VSD-fed CNC machines, a 60 % duty welding bay, lighting and soft-started HVAC at manufacturing diversity; every motor-driven load (motor, pumps, hvac) enters the starting check, and the soft-started 25 kW HVAC (62.5 kVA) outweighs the VSD CNC drive (36 kVA).

Given: Loads: CNC Machine 30 kW × 2 (motor, typical pf, VSD starting); Welding Bay 15 kW (welding, typical pf, duty 0.6); Lighting 8 kW (lighting, typical pf); HVAC 25 kW (hvac, typical pf, soft-start starting). Manufacturing facility (typical diversity); safety margin 1.25, largest-motor starting checked.

Load kVA	S_load = P × duty / pf × qty: CNC Machine: 30 / 0.87 × 2 = 68.97 kVA; Welding Bay: 15 × 0.6 / 0.7 = 12.86 kVA; Lighting: 8 / 0.95 = 8.42 kVA; HVAC: 25 / 0.88 = 28.41 kVA
Connected	S_total = 68.97 + 12.86 + 8.42 + 28.41 = 118.65 kVA; P_total = 102.00 kW; overall pf = 102.00 / 118.65 = 0.860
Running load	S_div = 118.65 × 0.75 (manufacturing) = 88.99 kVA (76.50 kW)
Starting demand	Largest starting kVA: HVAC 25 kW soft-start → S_start = 2.5 × 25 = 62.50 kVA; S_sd = 62.50 + 88.99 = 151.49 kVA
Sizing	S_req = max(88.99, 151.49) = 151.49 kVA → sized on starting; S_req × m = 151.49 × 1.25 = 189.36 kVA → next standard rating ≥ 189.36 = 200 kVA PASS
Utilisation	Running = 88.99 / 200 = 44.5 %; peak = 151.49 / 200 = 75.8 %
Fuel	F = 200 × 0.8 × (88.99 / 200) × 0.25 = 17.80 L/h
Result	1/1 checks pass → PASS; 200 kVA set, running utilisation 44.5 %; governing: motor starting
Reference	Hand calculation: S = 30/0.87 × 2 + 15 × 0.6/0.7 + 8/0.95 + 25/0.88 = 118.65 kVA; running = 118.65 × 0.75 = 88.99 kVA; start = 2.5 × 25 (HVAC, hvac) + 88.99 = 151.49 kVA; 151.49 × 1.25 = 189.36 → 200 kVA (starting); running utilisation = 88.99/200 = 44.5 %; peak = 151.49/200 = 75.7 %; fuel = 0.25 × 200 × 0.8 × 88.99/200 = 17.80 L/h (validation case `c0014-manufacturing-workshop`)

Example 9 — 400 kW heater bank with no safety margin

safety_margin 1.0 and a 400 kVA running load land exactly on the 400 kVA rating at 100 % utilisation, which triggers the high-utilisation warning.

Given: Loads: Heater bank 400 kW (resistive, typical pf). Essential services facility (typical diversity); safety margin 1, motor starting not checked.

Load kVA	S_load = P × duty / pf × qty: Heater bank: 400 / 1 = 400.00 kVA
Connected	S_total = 400.00 = 400.00 kVA; P_total = 400.00 kW; overall pf = 400.00 / 400.00 = 1.000
Running load	S_div = 400.00 × 1 (essential services) = 400.00 kVA (400.00 kW)
Starting demand	Motor starting not checked (include_motor_starting = no)
Sizing	S_req = S_div = 400.00 kVA → sized on running; S_req × m = 400.00 × 1 = 400.00 kVA → next standard rating ≥ 400.00 = 400 kVA PASS
Utilisation	Running = 400.00 / 400 = 100.0 %; peak = 400.00 / 400 = 100.0 %
Fuel	F = 400 × 0.8 × (400.00 / 400) × 0.25 = 80.00 L/h
Result	1/1 checks pass → PASS; 400 kVA set, running utilisation 100.0 %; governing: running load. High generator utilization: Limited margin for transients. Consider larger unit or load shedding strategy.
Reference	Hand calculation: S = 400/1 = 400.00 kVA; running = 400.00 × 1 = 400.00 kVA; 400.00 × 1 = 400.00 → 400 kVA (running); running utilisation = 400.00/400 = 100.0 %; fuel = 0.25 × 400 × 0.8 × 400.00/400 = 80.00 L/h (validation case `c0014-margin-1p0-on-rating`)

Example 10 — Hospital standby set with a 1.5 safety margin

A 75 kW DOL chiller at essential-services diversity with a 50 % margin and a 3000 L tank.

Given: Loads: Chiller 75 kW (motor, pf 0.85, DOL starting); Lighting 30 kW (lighting, typical pf); Medical equipment 40 kW (control, typical pf); AHU 20 kW × 2 (hvac, typical pf, DOL starting). Essential services facility (typical diversity); safety margin 1.5, largest-motor starting checked, fuel tank 3,000 L.

Load kVA	S_load = P × duty / pf × qty: Chiller: 75 / 0.85 = 88.24 kVA; Lighting: 30 / 0.95 = 31.58 kVA; Medical equipment: 40 / 1 = 40.00 kVA; AHU: 20 / 0.88 × 2 = 45.45 kVA
Connected	S_total = 88.24 + 31.58 + 40.00 + 45.45 = 205.27 kVA; P_total = 185.00 kW; overall pf = 185.00 / 205.27 = 0.901
Running load	S_div = 205.27 × 1 (essential services) = 205.27 kVA (185.00 kW)
Starting demand	Largest starting kVA: Chiller 75 kW DOL → S_start = 6 × 75 = 450.00 kVA; S_sd = 450.00 + 205.27 = 655.27 kVA
Sizing	S_req = max(205.27, 655.27) = 655.27 kVA → sized on starting; S_req × m = 655.27 × 1.5 = 982.90 kVA → next standard rating ≥ 982.90 = 1,000 kVA PASS
Utilisation	Running = 205.27 / 1,000 = 20.5 %; peak = 655.27 / 1,000 = 65.5 %
Fuel	F = 1,000 × 0.8 × (205.27 / 1,000) × 0.25 = 41.05 L/h; autonomy = 3,000 / 41.05 = 73.1 h
Result	1/1 checks pass → PASS; 1,000 kVA set, running utilisation 20.5 %; governing: motor starting. Install soft starter on Chiller: Reduce generator from 1000 kVA to 600 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 75/0.85 + 30/0.95 + 40/1 + 20/0.88 × 2 = 205.27 kVA; running = 205.27 × 1 = 205.27 kVA; start = 6 × 75 + 205.27 = 655.27 kVA; 655.27 × 1.5 = 982.90 → 1000 kVA (starting); running utilisation = 205.27/1000 = 20.5 %; peak = 655.27/1000 = 65.5 %; fuel = 0.25 × 1000 × 0.8 × 205.27/1000 = 41.05 L/h; autonomy = 3000/41.05 = 73.1 h (validation case `c0014-margin-1p5-hospital`)

Example 11 — Eight 22 kW motors with motor starting excluded

With include_motor_starting false the set is sized on the diversified running load alone, even though DOL motors are present.

Given: Loads: Conveyor motors 22 kW × 8 (motor, typical pf, DOL starting); Resistive heating 50 kW (resistive, typical pf). Manufacturing facility (typical diversity); safety margin 1.25, motor starting not checked.

Load kVA	S_load = P × duty / pf × qty: Conveyor motors: 22 / 0.87 × 8 = 202.30 kVA; Resistive heating: 50 / 1 = 50.00 kVA
Connected	S_total = 202.30 + 50.00 = 252.30 kVA; P_total = 226.00 kW; overall pf = 226.00 / 252.30 = 0.896
Running load	S_div = 252.30 × 0.75 (manufacturing) = 189.23 kVA (169.50 kW)
Starting demand	Motor starting not checked (include_motor_starting = no)
Sizing	S_req = S_div = 189.23 kVA → sized on running; S_req × m = 189.23 × 1.25 = 236.54 kVA → next standard rating ≥ 236.54 = 250 kVA PASS
Utilisation	Running = 189.23 / 250 = 75.7 %; peak = 189.23 / 250 = 75.7 %
Fuel	F = 250 × 0.8 × (189.23 / 250) × 0.25 = 37.85 L/h
Result	1/1 checks pass → PASS; 250 kVA set, running utilisation 75.7 %; governing: running load
Reference	Hand calculation: S = 22/0.87 × 8 + 50/1 = 252.30 kVA; running = 252.30 × 0.75 = 189.23 kVA; 189.23 × 1.25 = 236.54 → 250 kVA (running); running utilisation = 189.23/250 = 75.7 %; fuel = 0.25 × 250 × 0.8 × 189.23/250 = 37.85 L/h (validation case `c0014-no-starting-check`)

Example 12 — Cold store with three DOL compressors on four units

Four 350 kVA units fail the N−1 check against a 1166 kVA DOL starting demand; the tool also recommends a soft starter.

Given: Loads: Refrigeration compressor 110 kW × 3 (motor, pf 0.88, DOL starting); Evaporator fans 30 kW × 4 (hvac, typical pf, DOL starting); Lighting 20 kW (lighting, typical pf). Continuous process facility (typical diversity); safety margin 1.25, largest-motor starting checked, 4 identical units in parallel.

Load kVA	S_load = P × duty / pf × qty: Refrigeration compressor: 110 / 0.88 × 3 = 375.00 kVA; Evaporator fans: 30 / 0.88 × 4 = 136.36 kVA; Lighting: 20 / 0.95 = 21.05 kVA
Connected	S_total = 375.00 + 136.36 + 21.05 = 532.42 kVA; P_total = 470.00 kW; overall pf = 470.00 / 532.42 = 0.883
Running load	S_div = 532.42 × 0.95 (continuous process) = 505.80 kVA (446.50 kW)
Starting demand	Largest starting kVA: Refrigeration compressor 110 kW DOL → S_start = 6 × 110 = 660.00 kVA; S_sd = 660.00 + 505.80 = 1,165.80 kVA
Sizing	S_req = max(505.80, 1,165.80) = 1,165.80 kVA → sized on starting; S_req × m = 1,165.80 × 1.25 = 1,457.25 kVA → next standard rating ≥ 1,457.25 = 1,500 kVA PASS
Utilisation	Running = 505.80 / 1,500 = 33.7 %; peak = 1,165.80 / 1,500 = 77.7 %
Fuel	F = 1,500 × 0.8 × (505.80 / 1,500) × 0.25 = 101.16 L/h
Parallel set	Unit = next standard ≥ 1.1 × 1,165.80 / 4 = 320.60 → 350 kVA; 4 × 350 = 1,400 kVA; N−1 = 3 × 350 = 1,050 kVA vs S_req 1,165.80 kVA (111.0 %) FAIL
Result	1/2 checks pass → FAIL; 1,500 kVA set, running utilisation 33.7 %; governing: motor starting. Install soft starter on Refrigeration compressor: Reduce generator from 1500 kVA to 1000 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 110/0.88 × 3 + 30/0.88 × 4 + 20/0.95 = 532.42 kVA; running = 532.42 × 0.95 = 505.80 kVA; start = 6 × 110 + 505.80 = 1165.80 kVA; 1165.80 × 1.25 = 1457.25 → 1500 kVA (starting); running utilisation = 505.80/1500 = 33.7 %; peak = 1165.80/1500 = 77.7 %; fuel = 0.25 × 1500 × 0.8 × 505.80/1500 = 101.16 L/h; parallel 4 units: 1.1 × 1165.80/4 = 320.60 → 350 kVA each, N−1 = 1050 kVA < 1165.80 kVA (validation case `c0014-parallel-four-units-fail`)

Example 13 — Four parallel units with a soft-started crusher

Four 250 kVA units give 750 kVA with one out, above the 735 kVA starting demand, so N−1 passes.

Given: Loads: Crusher 90 kW (motor, pf 0.9, soft-start starting); Process heaters 410 kW (resistive, typical pf). Essential services facility (typical diversity); safety margin 1.25, largest-motor starting checked, 4 identical units in parallel.

Load kVA	S_load = P × duty / pf × qty: Crusher: 90 / 0.9 = 100.00 kVA; Process heaters: 410 / 1 = 410.00 kVA
Connected	S_total = 100.00 + 410.00 = 510.00 kVA; P_total = 500.00 kW; overall pf = 500.00 / 510.00 = 0.980
Running load	S_div = 510.00 × 1 (essential services) = 510.00 kVA (500.00 kW)
Starting demand	Largest starting kVA: Crusher 90 kW soft-start → S_start = 2.5 × 90 = 225.00 kVA; S_sd = 225.00 + 510.00 = 735.00 kVA
Sizing	S_req = max(510.00, 735.00) = 735.00 kVA → sized on starting; S_req × m = 735.00 × 1.25 = 918.75 kVA → next standard rating ≥ 918.75 = 1,000 kVA PASS
Utilisation	Running = 510.00 / 1,000 = 51.0 %; peak = 735.00 / 1,000 = 73.5 %
Fuel	F = 1,000 × 0.8 × (510.00 / 1,000) × 0.25 = 102.00 L/h
Parallel set	Unit = next standard ≥ 1.1 × 735.00 / 4 = 202.13 → 250 kVA; 4 × 250 = 1,000 kVA; N−1 = 3 × 250 = 750 kVA vs S_req 735.00 kVA (98.0 %) PASS
Result	2/2 checks pass → PASS; 1,000 kVA set, running utilisation 51.0 %; governing: motor starting
Reference	Hand calculation: S = 90/0.9 + 410/1 = 510.00 kVA; running = 510.00 × 1 = 510.00 kVA; start = 2.5 × 90 + 510.00 = 735.00 kVA; 735.00 × 1.25 = 918.75 → 1000 kVA (starting); running utilisation = 510.00/1000 = 51.0 %; peak = 735.00/1000 = 73.5 %; fuel = 0.25 × 1000 × 0.8 × 510.00/1000 = 102.00 L/h; parallel 4 units: 1.1 × 735.00/4 = 202.13 → 250 kVA each, N−1 = 750 kVA ≥ 735.00 kVA (validation case `c0014-parallel-four-units-pass`)

Example 14 — Three parallel units carrying the load with one out

Three 100 kVA units: the N−1 capacity equals the 200 kVA starting demand exactly, so the parallel check passes on the boundary.

Given: Loads: Fan 20 kW (motor, pf 0.8, DOL starting); Heaters 55 kW (resistive, typical pf). Essential services facility (typical diversity); safety margin 1.25, largest-motor starting checked, 3 identical units in parallel.

Load kVA	S_load = P × duty / pf × qty: Fan: 20 / 0.8 = 25.00 kVA; Heaters: 55 / 1 = 55.00 kVA
Connected	S_total = 25.00 + 55.00 = 80.00 kVA; P_total = 75.00 kW; overall pf = 75.00 / 80.00 = 0.938
Running load	S_div = 80.00 × 1 (essential services) = 80.00 kVA (75.00 kW)
Starting demand	Largest starting kVA: Fan 20 kW DOL → S_start = 6 × 20 = 120.00 kVA; S_sd = 120.00 + 80.00 = 200.00 kVA
Sizing	S_req = max(80.00, 200.00) = 200.00 kVA → sized on starting; S_req × m = 200.00 × 1.25 = 250.00 kVA → next standard rating ≥ 250.00 = 250 kVA PASS
Utilisation	Running = 80.00 / 250 = 32.0 %; peak = 200.00 / 250 = 80.0 %
Fuel	F = 250 × 0.8 × (80.00 / 250) × 0.25 = 16.00 L/h
Parallel set	Unit = next standard ≥ 1.1 × 200.00 / 3 = 73.33 → 100 kVA; 3 × 100 = 300 kVA; N−1 = 2 × 100 = 200 kVA vs S_req 200.00 kVA (100.0 %) PASS
Result	2/2 checks pass → PASS; 250 kVA set, running utilisation 32.0 %; governing: motor starting. Install soft starter on Fan: Reduce generator from 250 kVA to 175 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 20/0.8 + 55/1 = 80.00 kVA; running = 80.00 × 1 = 80.00 kVA; start = 6 × 20 + 80.00 = 200.00 kVA; 200.00 × 1.25 = 250.00 → 250 kVA (starting); running utilisation = 80.00/250 = 32.0 %; peak = 200.00/250 = 80.0 %; fuel = 0.25 × 250 × 0.8 × 80.00/250 = 16.00 L/h; parallel 3 units: 1.1 × 200.00/3 = 73.33 → 100 kVA each, N−1 = 200 kVA ≥ 200.00 kVA (validation case `c0014-parallel-three-units-pass`)

Example 15 — 500 kVA essential load on two parallel units

The help page's parallel example: a 500 kVA running load split over two units gives 300 kVA each, which cannot carry the load with one unit out.

Given: Loads: Process heaters 500 kW (resistive, typical pf). Essential services facility (typical diversity); safety margin 1.25, motor starting not checked, 2 identical units in parallel.

Load kVA	S_load = P × duty / pf × qty: Process heaters: 500 / 1 = 500.00 kVA
Connected	S_total = 500.00 = 500.00 kVA; P_total = 500.00 kW; overall pf = 500.00 / 500.00 = 1.000
Running load	S_div = 500.00 × 1 (essential services) = 500.00 kVA (500.00 kW)
Starting demand	Motor starting not checked (include_motor_starting = no)
Sizing	S_req = S_div = 500.00 kVA → sized on running; S_req × m = 500.00 × 1.25 = 625.00 kVA → next standard rating ≥ 625.00 = 750 kVA PASS
Utilisation	Running = 500.00 / 750 = 66.7 %; peak = 500.00 / 750 = 66.7 %
Fuel	F = 750 × 0.8 × (500.00 / 750) × 0.25 = 100.00 L/h
Parallel set	Unit = next standard ≥ 1.1 × 500.00 / 2 = 275.00 → 300 kVA; 2 × 300 = 600 kVA; N−1 = 1 × 300 = 300 kVA vs S_req 500.00 kVA (166.7 %) FAIL
Result	1/2 checks pass → FAIL; 750 kVA set, running utilisation 66.7 %; governing: running load
Reference	Hand calculation: S = 500/1 = 500.00 kVA; running = 500.00 × 1 = 500.00 kVA; 500.00 × 1.25 = 625.00 → 750 kVA (running); running utilisation = 500.00/750 = 66.7 %; fuel = 0.25 × 750 × 0.8 × 500.00/750 = 100.00 L/h; parallel 2 units: 1.1 × 500.00/2 = 275.00 → 300 kVA each, N−1 = 300 kVA < 500.00 kVA (validation case `c0014-parallel-two-units-500kva`)

Example 16 — Small shop on two 100 kVA units, no motors

With no motor-driven loads (motor, pumps, hvac) the starting demand equals the running load and sizing is on running; two 100 kVA units pass N−1 against 80 kVA.

Given: Loads: Shop lighting 28.5 kW (lighting, typical pf); IT and control 22 kW (control, pf 0.88); Office 45 kW (resistive, typical pf). Commercial facility (typical diversity); safety margin 1.25, largest-motor starting checked, 2 identical units in parallel.

Load kVA	S_load = P × duty / pf × qty: Shop lighting: 28.5 / 0.95 = 30.00 kVA; IT and control: 22 / 0.88 = 25.00 kVA; Office: 45 / 1 = 45.00 kVA
Connected	S_total = 30.00 + 25.00 + 45.00 = 100.00 kVA; P_total = 95.50 kW; overall pf = 95.50 / 100.00 = 0.955
Running load	S_div = 100.00 × 0.8 (commercial) = 80.00 kVA (76.40 kW)
Starting demand	No motor-driven loads (motor, pumps, hvac) → S_sd = 0 + 80.00 = 80.00 kVA
Sizing	S_req = max(80.00, 80.00) = 80.00 kVA → sized on running; S_req × m = 80.00 × 1.25 = 100.00 kVA → next standard rating ≥ 100.00 = 100 kVA PASS
Utilisation	Running = 80.00 / 100 = 80.0 %; peak = 80.00 / 100 = 80.0 %
Fuel	F = 100 × 0.8 × (80.00 / 100) × 0.25 = 16.00 L/h
Parallel set	Unit = next standard ≥ 1.1 × 80.00 / 2 = 44.00 → 100 kVA; 2 × 100 = 200 kVA; N−1 = 1 × 100 = 100 kVA vs S_req 80.00 kVA (80.0 %) PASS
Result	2/2 checks pass → PASS; 100 kVA set, running utilisation 80.0 %; governing: running load
Reference	Hand calculation: S = 28.5/0.95 + 22/0.88 + 45/1 = 100.00 kVA; running = 100.00 × 0.8 = 80.00 kVA; no motor-driven (motor/pumps/hvac) loads, so starting demand = running load; 80.00 × 1.25 = 100.00 → 100 kVA (running); running utilisation = 80.00/100 = 80.0 %; fuel = 0.25 × 100 × 0.8 × 80.00/100 = 16.00 L/h; parallel 2 units: 1.1 × 80.00/2 = 44.00 → 100 kVA each, N−1 = 100 kVA ≥ 80.00 kVA (validation case `c0014-parallel-two-units-small-shop`)

Example 17 — Smaller DOL agitator out-starts a larger star-delta mixer

The starting check takes the largest starting kVA, not the largest motor: 45 kW DOL (270 kVA) beats 90 kW star-delta (180 kVA).

Given: Loads: Mixer 90 kW (motor, pf 0.88, star-delta starting); Agitator 45 kW (motor, pf 0.85, DOL starting); Heater 30 kW (resistive, typical pf). Continuous process facility (typical diversity); safety margin 1.25, largest-motor starting checked.

Load kVA	S_load = P × duty / pf × qty: Mixer: 90 / 0.88 = 102.27 kVA; Agitator: 45 / 0.85 = 52.94 kVA; Heater: 30 / 1 = 30.00 kVA
Connected	S_total = 102.27 + 52.94 + 30.00 = 185.21 kVA; P_total = 165.00 kW; overall pf = 165.00 / 185.21 = 0.891
Running load	S_div = 185.21 × 0.95 (continuous process) = 175.95 kVA (156.75 kW)
Starting demand	Largest starting kVA: Agitator 45 kW DOL → S_start = 6 × 45 = 270.00 kVA; S_sd = 270.00 + 175.95 = 445.95 kVA
Sizing	S_req = max(175.95, 445.95) = 445.95 kVA → sized on starting; S_req × m = 445.95 × 1.25 = 557.44 kVA → next standard rating ≥ 557.44 = 600 kVA PASS
Utilisation	Running = 175.95 / 600 = 29.3 %; peak = 445.95 / 600 = 74.3 %
Fuel	F = 600 × 0.8 × (175.95 / 600) × 0.25 = 35.19 L/h
Result	1/1 checks pass → PASS; 600 kVA set, running utilisation 29.3 %; governing: motor starting. Install soft starter on Agitator: Reduce generator from 600 kVA to 400 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 90/0.88 + 45/0.85 + 30/1 = 185.21 kVA; running = 185.21 × 0.95 = 175.95 kVA; start = 6 × 45 + 175.95 = 445.95 kVA; 445.95 × 1.25 = 557.44 → 600 kVA (starting); running utilisation = 175.95/600 = 29.3 %; peak = 445.95/600 = 74.3 %; fuel = 0.25 × 600 × 0.8 × 175.95/600 = 35.19 L/h (validation case `c0014-smaller-dol-motor-governs`)

Example 18 — 160 kW soft-started borehole pump

A soft starter (2.5 × kW) on the largest motor keeps the starting demand within a 750 kVA set for an essential-services site.

Given: Loads: Borehole pump 160 kW (motor, pf 0.9, soft-start starting); Dosing pump 7.5 kW (motor, typical pf, DOL starting); Lighting 4 kW (lighting, typical pf); Control 3 kW (control, typical pf). Essential services facility (typical diversity); safety margin 1.25, largest-motor starting checked.

Load kVA	S_load = P × duty / pf × qty: Borehole pump: 160 / 0.9 = 177.78 kVA; Dosing pump: 7.5 / 0.87 = 8.62 kVA; Lighting: 4 / 0.95 = 4.21 kVA; Control: 3 / 1 = 3.00 kVA
Connected	S_total = 177.78 + 8.62 + 4.21 + 3.00 = 193.61 kVA; P_total = 174.50 kW; overall pf = 174.50 / 193.61 = 0.901
Running load	S_div = 193.61 × 1 (essential services) = 193.61 kVA (174.50 kW)
Starting demand	Largest starting kVA: Borehole pump 160 kW soft-start → S_start = 2.5 × 160 = 400.00 kVA; S_sd = 400.00 + 193.61 = 593.61 kVA
Sizing	S_req = max(193.61, 593.61) = 593.61 kVA → sized on starting; S_req × m = 593.61 × 1.25 = 742.01 kVA → next standard rating ≥ 742.01 = 750 kVA PASS
Utilisation	Running = 193.61 / 750 = 25.8 %; peak = 593.61 / 750 = 79.2 %
Fuel	F = 750 × 0.8 × (193.61 / 750) × 0.25 = 38.72 L/h
Result	1/1 checks pass → PASS; 750 kVA set, running utilisation 25.8 %; governing: motor starting. Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 160/0.9 + 7.5/0.87 + 4/0.95 + 3/1 = 193.61 kVA; running = 193.61 × 1 = 193.61 kVA; start = 2.5 × 160 + 193.61 = 593.61 kVA; 593.61 × 1.25 = 742.01 → 750 kVA (starting); running utilisation = 193.61/750 = 25.8 %; peak = 593.61/750 = 79.2 %; fuel = 0.25 × 750 × 0.8 × 193.61/750 = 38.72 L/h (validation case `c0014-soft-start-borehole-pump`)

Example 19 — 132 kW star-delta compressor governs starting

A star-delta compressor (2 × kW) still out-starts a 30 kW DOL conveyor; the oversized set runs below 40 % and the tool warns of wet stacking.

Given: Loads: Compressor 132 kW (motor, pf 0.9, star-delta starting); Conveyor 30 kW (motor, typical pf, DOL starting); Lighting 10 kW (lighting, typical pf). Manufacturing facility (typical diversity); safety margin 1.25, largest-motor starting checked.

Load kVA	S_load = P × duty / pf × qty: Compressor: 132 / 0.9 = 146.67 kVA; Conveyor: 30 / 0.87 = 34.48 kVA; Lighting: 10 / 0.95 = 10.53 kVA
Connected	S_total = 146.67 + 34.48 + 10.53 = 191.68 kVA; P_total = 172.00 kW; overall pf = 172.00 / 191.68 = 0.897
Running load	S_div = 191.68 × 0.75 (manufacturing) = 143.76 kVA (129.00 kW)
Starting demand	Largest starting kVA: Compressor 132 kW star-delta → S_start = 2 × 132 = 264.00 kVA; S_sd = 264.00 + 143.76 = 407.76 kVA
Sizing	S_req = max(143.76, 407.76) = 407.76 kVA → sized on starting; S_req × m = 407.76 × 1.25 = 509.70 kVA → next standard rating ≥ 509.70 = 600 kVA PASS
Utilisation	Running = 143.76 / 600 = 24.0 %; peak = 407.76 / 600 = 68.0 %
Fuel	F = 600 × 0.8 × (143.76 / 600) × 0.25 = 28.75 L/h
Result	1/1 checks pass → PASS; 600 kVA set, running utilisation 24.0 %; governing: motor starting. Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 132/0.9 + 30/0.87 + 10/0.95 = 191.68 kVA; running = 191.68 × 0.75 = 143.76 kVA; start = 2 × 132 + 143.76 = 407.76 kVA; 407.76 × 1.25 = 509.70 → 600 kVA (starting); running utilisation = 143.76/600 = 24.0 %; peak = 407.76/600 = 68.0 %; fuel = 0.25 × 600 × 0.8 × 143.76/600 = 28.75 L/h (validation case `c0014-star-delta-compressor-governs`)

Example 20 — Water pumping station (continuous process)

The help page's pumping-station example: a 110 kW DOL main pump beside a star-delta jockey pump, control and lighting, with a 2000 L tank.

Given: Loads: Main Pump 110 kW (motor, pf 0.89, DOL starting); Jockey Pump 22 kW (motor, pf 0.86, star-delta starting); Control Panel 3 kW (control, typical pf); Lighting 5 kW (lighting, typical pf). Continuous process facility (typical diversity); safety margin 1.25, largest-motor starting checked, fuel tank 2,000 L.

Load kVA	S_load = P × duty / pf × qty: Main Pump: 110 / 0.89 = 123.60 kVA; Jockey Pump: 22 / 0.86 = 25.58 kVA; Control Panel: 3 / 1 = 3.00 kVA; Lighting: 5 / 0.95 = 5.26 kVA
Connected	S_total = 123.60 + 25.58 + 3.00 + 5.26 = 157.44 kVA; P_total = 140.00 kW; overall pf = 140.00 / 157.44 = 0.889
Running load	S_div = 157.44 × 0.95 (continuous process) = 149.57 kVA (133.00 kW)
Starting demand	Largest starting kVA: Main Pump 110 kW DOL → S_start = 6 × 110 = 660.00 kVA; S_sd = 660.00 + 149.57 = 809.57 kVA
Sizing	S_req = max(149.57, 809.57) = 809.57 kVA → sized on starting; S_req × m = 809.57 × 1.25 = 1,011.96 kVA → next standard rating ≥ 1,011.96 = 1,250 kVA PASS
Utilisation	Running = 149.57 / 1,250 = 12.0 %; peak = 809.57 / 1,250 = 64.8 %
Fuel	F = 1,250 × 0.8 × (149.57 / 1,250) × 0.25 = 29.91 L/h; autonomy = 2,000 / 29.91 = 66.9 h
Result	1/1 checks pass → PASS; 1,250 kVA set, running utilisation 12.0 %; governing: motor starting. Install soft starter on Main Pump: Reduce generator from 1250 kVA to 600 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 110/0.89 + 22/0.86 + 3/1 + 5/0.95 = 157.44 kVA; running = 157.44 × 0.95 = 149.57 kVA; start = 6 × 110 + 149.57 = 809.57 kVA; 809.57 × 1.25 = 1011.96 → 1250 kVA (starting); running utilisation = 149.57/1250 = 12.0 %; peak = 809.57/1250 = 64.8 %; fuel = 0.25 × 1250 × 0.8 × 149.57/1250 = 29.91 L/h; autonomy = 2000/29.91 = 66.9 h (validation case `c0014-water-pumping-station`)

Example 21 — Welding shop with 50 % duty welders and pump loads

Four welders at 50 % duty and pf 0.7, a pumps-type load (not starting-checked) and a 15 kW DOL compressor that governs starting.

Given: Loads: Welders 25 kW × 4 (welding, typical pf, duty 0.5); Compressor 15 kW (motor, typical pf, DOL starting); Cooling pumps 5.5 kW × 2 (pumps, typical pf, DOL starting); Lighting 6 kW (lighting, typical pf). Manufacturing facility (typical diversity); safety margin 1.25, largest-motor starting checked.

Load kVA	S_load = P × duty / pf × qty: Welders: 25 × 0.5 / 0.7 × 4 = 71.43 kVA; Compressor: 15 / 0.87 = 17.24 kVA; Cooling pumps: 5.5 / 0.88 × 2 = 12.50 kVA; Lighting: 6 / 0.95 = 6.32 kVA
Connected	S_total = 71.43 + 17.24 + 12.50 + 6.32 = 107.49 kVA; P_total = 82.00 kW; overall pf = 82.00 / 107.49 = 0.763
Running load	S_div = 107.49 × 0.75 (manufacturing) = 80.62 kVA (61.50 kW)
Starting demand	Largest starting kVA: Compressor 15 kW DOL → S_start = 6 × 15 = 90.00 kVA; S_sd = 90.00 + 80.62 = 170.62 kVA
Sizing	S_req = max(80.62, 170.62) = 170.62 kVA → sized on starting; S_req × m = 170.62 × 1.25 = 213.28 kVA → next standard rating ≥ 213.28 = 250 kVA PASS
Utilisation	Running = 80.62 / 250 = 32.2 %; peak = 170.62 / 250 = 68.2 %
Fuel	F = 250 × 0.8 × (80.62 / 250) × 0.25 = 16.12 L/h
Result	1/1 checks pass → PASS; 250 kVA set, running utilisation 32.2 %; governing: motor starting. Install soft starter on Compressor: Reduce generator from 250 kVA to 150 kVA Low generator utilization: Risk of wet stacking in diesel engines. Consider smaller unit or load management.
Reference	Hand calculation: S = 25 × 0.5/0.7 × 4 + 15/0.87 + 5.5/0.88 × 2 + 6/0.95 = 107.49 kVA; running = 107.49 × 0.75 = 80.62 kVA; start = 6 × 15 + 80.62 = 170.62 kVA; 170.62 × 1.25 = 213.28 → 250 kVA (starting); running utilisation = 80.62/250 = 32.2 %; peak = 170.62/250 = 68.2 %; fuel = 0.25 × 250 × 0.8 × 80.62/250 = 16.12 L/h (validation case `c0014-welding-shop-duty-cycle`)

Standards & References

IEC 60034 — Rotating electrical machines — motor starting characteristics and ratings
ISO 8528 — Reciprocating internal combustion engine driven alternating current generating sets
Manufacturer guidelines — Caterpillar, Cummins, FG Wilson generator sizing application guides
Industry practice — diversity factors and safety margins based on engineering handbooks and real-world project experience
Fuel consumption — based on typical diesel generator specific fuel consumption of 0.25 L/kWh at rated load

Tips & Limitations

Tips

DOL-started motors often drive generator sizing far beyond the running load. Adding a soft starter on the largest motor can reduce the required generator size significantly.
Optimal generator utilization is 60–80%. This provides adequate margin for transients while avoiding wet stacking in diesel engines.
If the power factor of a load is not known, the calculator uses typical values (e.g., 0.87 for motors, 0.70 for welding). These are conservative — actual values may be higher.
For intermittent loads (e.g., welding at 60% duty cycle), set the duty cycle to reduce the effective running load contribution.
Fuel autonomy calculations assume a constant load. In practice, load variation will extend actual autonomy somewhat.
Essential services (hospitals, fire systems) should use a diversity factor of 1.0 — assume all loads run simultaneously.
For parallel generator configurations, consider N+1 redundancy so one unit can be taken offline for maintenance.

Limitations

Steady-state analysis — the calculator does not model transient voltage dip or frequency recovery during motor starting events.
No harmonic derating — VSD and other non-linear loads may require generator derating for harmonics, which is not modelled.
No altitude/temperature derating — generators at high altitude or elevated ambient temperatures require capacity derating per manufacturer data.
Simplified fuel model — actual fuel consumption varies with load profile, generator efficiency, altitude, and fuel quality. The 0.25 L/kWh figure is approximate.
Single starting event — only the motor-driven load (motor, pumps or hvac) with the largest starting kVA is considered. Simultaneous starting of multiple motors is not analysed.
No load sequencing — the calculator does not model sequential load application (block loading) on generator startup.
Generator sizes above 5000 kVA are rounded up to the nearest 100 kVA rather than matched to a standard catalogue size.

Developer Guide

Architecture

File layout:

components/c0014_generator_sizing/component.py — Component registration, parameter schema, calculator class, equation builder, summary cards builder
components/c0014_generator_sizing/calculations.py — Pure calculation functions, constants, and data tables (no Django dependencies)
components/c0014_generator_sizing/equations.py — Builds the unified article structure for report output

The calculator class is GeneratorSizingCalculator, inheriting from ElectricalCalculator. It delegates all math to the pure functions in calculations.py.

Key constants are defined as Python dicts in calculations.py:

STARTING_MULTIPLIERS — motor starting kVA multipliers by method
TYPICAL_POWER_FACTORS — default power factors by load type
DIVERSITY_FACTORS — diversity factors by facility type
STANDARD_GENERATOR_SIZES — list of standard generator sizes (100–5000 kVA)

Code Paths

Key functions in calculations.py:

Function	Purpose
`calculate_load_kva(power_kw, pf, duty_cycle)`	Convert kW to kVA with duty cycle
`calculate_motor_starting_kva(power_kw, starting_method)`	Calculate motor starting kVA demand
`analyze_load_inventory(loads)`	Sum all connected loads and calculate totals
`calculate_running_load(loads, diversity_factor)`	Apply diversity factor to total connected load
`calculate_starting_load(loads, background_kva)`	Find worst-case motor starting scenario
`select_standard_generator_size(required_kva, margin)`	Select next standard size with safety margin
`calculate_fuel_consumption(generator_kva, load_factor)`	Estimate diesel fuel consumption (L/hr)
`calculate_fuel_autonomy(generator_kva, load_factor, tank)`	Calculate hours of fuel autonomy
`calculate_parallel_generators(total_kva, num_generators)`	Evaluate parallel generator configuration
`calculate_generator_sizing(data)`	Main orchestration function — calls all of the above

Key methods in component.py:

Function / Method	Purpose
`GeneratorSizingCalculator.validate_parameters()`	Validate loads array, safety margin, custom diversity
`GeneratorSizingCalculator.calculate()`	Orchestrate calculation with fuel and parallel analysis
`equation_builder(results)`	Build unified article structure for report generation
`summary_cards_builder(results)`	Build dashboard summary cards (generator size, utilization, fuel)

Testing

Running tests:

pytest calcs/components/c0014_generator_sizing/ -v
pytest calcs/test_c0014* -v

Worked examples: the examples above are generated from the validation corpus in mcp_public/validation/cases/fe_calc_generator/ by python manage.py generate_help_examples --tool fe_calc_generator (renderer calcs/core/help_examples/generator.py). Do not edit _generator_sizing_examples.html by hand; add or change a case and regenerate.

How to extend:

Add new load types by extending the TYPICAL_POWER_FACTORS dict and adding the new value to the load_type enum in the parameter schema.
Add new starting methods by extending STARTING_MULTIPLIERS and the starting_method enum.
Add new facility types by extending DIVERSITY_FACTORS and the facility_type enum.
Extend standard sizes by adding values to STANDARD_GENERATOR_SIZES (keep sorted).
For temperature/altitude derating, add a derating factor to select_standard_generator_size() and expose new input parameters in the schema.
Write tests covering new constants, edge cases (empty loads, single load, all-motor loads), and boundary conditions (utilization near 40% and 90% thresholds).