Generator Cable Size Calculator

What this calculator measures

Estimate conductor area for the entered lagging-PF voltage-drop model using the correct single-phase or balanced three-phase relationship. This is not an ampacity, protection, AWG, or installation approval.

Inputs and units

Use readings and ratings that describe the same equipment, operating interval, and measurement boundary. The sample entries are editable examples; they do not establish the specifications of your generator.

Calculation method

The model uses line current = real W ÷ (V × PF) for single phase, or real W ÷ (√3 × V × PF) for balanced three phase. Longitudinal voltage drop is 2IL(R cosφ + X sinφ) for the two-wire circuit and √3IL(R cosφ + X sinφ) for balanced three phase.

With cosφ = PF and sinφ = √(1 − PF²), solve the resistance term for cross-sectional area in mm². Use conductor resistivity in ohm mm²/m and reactance per metre on the same temperature and length basis. If the assumed reactive drop already consumes the entire drop budget, no finite area solves this constant-reactance model and the tool reports a calculation failure.

Worked example

With 10 kW, 400 V, balanced three phase, 50 m one-way length, PF 1, a 3% run-drop budget, and an assumed resistivity of 0.0237 ohm mm²/m, the area estimate is 2.47 mm². Reactance contributes no longitudinal drop at PF 1 in this model. This result does not establish that a 2.5 mm² installation meets ampacity or any other requirement.

Limitations and checks

Use the conductor manufacturer’s operating-temperature resistance and configuration-specific reactance. The defaults illustrate assumptions. This approximate steady-load voltage-drop calculation does not check ampacity, fault duty, protective coordination, conductor availability, neutral current, mechanical installation, or motor-start voltage dip. A calculated area is not a selected cable.

For a practical decision, keep the original readings, the generator model, the relevant manual or specification, and the assumptions alongside the result. A different load, site condition, rating basis, or unit convention can answer a different question even when the arithmetic is correct.

Sources and methodology

• Schneider Electric Electrical Installation Guide: voltage-drop relationships

Publisher: CSP Digital Media Ltd. To report a formula, unit, or example error, contact us with the tool name, inputs, displayed result, and expected calculation.