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Generator running load and startup surge

Job / reference: ______________________________Printed date: ____

Formula registry version 1.0.0 · researched 2026-07-24

PS-04 · Power & supply

Generator running load and startup surge

Enter electrical input power, power factor and a manufacturer or scenario startup multiplier. Select exactly which load starts while the others run.

PLANNING ESTIMATE

Entered loads and startup scenario

Load 1
Load 2

Method and worked example

S_run = Σ(Pᵢ ÷ PFᵢ)

S_start,j = (Pⱼ × Mⱼ ÷ PFⱼ) + Σ(i≠j)(Pᵢ ÷ PFᵢ)

S_plan = S_start × (1 + margin ÷ 100)

Worked example: 1.6 kW / PF 0.9 starts at entered 2.5× while 0.8 kW / PF 0.8 runs: 2.778 kVA running, 5.444 kVA startup peak and 6.533 kVA with an entered 20% margin.

Blank worksheet

Load / input kW / PF / start multiplier:
Selected startup load:
Running sum:
Startup peak:
Entered margin / planned figure:

Generator demand result

Result recordPLANNING ESTIMATE

Worked example — default entered values

2.778 kVA running
5.444 kVA startup peak
6.533 kVA with entered margin

Load 1 starts at 2.5×; entered margin 20%. Manufacturer transient confirmation required.

Assumptions register

Load 1: 1.6 kW ÷ PF 0.9 = 1.778 kVA · selected start 2.5× · Load 2: 0.8 kW ÷ PF 0.8 = 1.000 kVA · Entered margin: 20% · Entered environment/location scenario: Outdoors in an open, manufacturer-permitted location

One explicitly selected load starts while every other entered load is already running.

Each startup multiplier is entered by the user; it is not a universal motor value.

Startup power factor is approximated by the entered running power factor.

Waveform, voltage/frequency dip, phase, earthing, nonlinear loads and altitude/temperature derating are not modelled.

△ Manufacturer data governs

Confirm nameplate input, phase, voltage, frequency, waveform, earthing, transient kVA, voltage dip, load-step limits and derating. Sensitive, nonlinear, welding, lifting or critical loads require specialist assessment.

PLANNING ESTIMATE. Nameplates, waveform, phase, voltage, frequency, earthing and manufacturer transient/load-step limits govern. Never convert the result directly into a generator product size.

Source register · registry version 1.0.0

Cummins, How to size a genset: Proper generator set sizing requires analysis of parameters and loads — effective 2007-07-01 — accessed 2026-07-24

Cummins, T-030: Liquid-Cooled Generator Set Application Manual — effective 2015-02-01 — accessed 2026-07-24

Health and Safety Executive, Construction hazardous substances: Carbon monoxide — accessed 2026-07-24

Formula researched 2026-07-24