Generator Wire 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 circular-mil area. Use copper K in ohm cmil/ft and reactance per foot 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

For a 100 kW, 240 V single-phase load at PF 1, 100 ft one-way run, a 3% drop budget, and K = 12.9, the area estimate is approximately 149,305.56 cmil. The two-wire return path is included. The number is an area, not an AWG recommendation or an ampacity approval.

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.