Cable current calculator

Convert load power to full-load line current before sizing cable, breakers and connectors. Enter power in kilowatts or horsepower, the line voltage and power factor, then read the current for single-phase and three-phase circuits — with the same load at common nominal voltages.

Load power

Line voltage

Line-to-line for three-phase

Circuit type

I = P ÷ (√3 × V × PF), using line-to-line voltage

Power factor (PF)

Resistive loads: 1.0; typical motors: 0.8–0.9

Result

Full-load line current: 18.7A

Three-phase circuits carry this current per phase — each conductor is sized for it. The result is the minimum rating for the cable, circuit breaker and connector. Real installations add a service factor (typically 125 %) and de-rating for bundling and ambient temperature.

At common line voltages

The same load at the standard nominal voltages:

Voltage	Current
230 V (three-phase)	32.5 A
400 V (three-phase)	18.7 A
480 V (three-phase)	15.6 A

Size the whole path

The connector and cable must both carry the current you just calculated: power connectors, terminal blocks and power cable are all rated by current capacity.

Frequently asked questions

How do you calculate full-load current from kW for a three-phase motor?

Three-phase current is I = P × 1000 ÷ (√3 × V × PF) using line-to-line voltage. At the defaults — 11 kW, 400 V, power factor 0.85 — that gives about 18.7 A per phase, which is the value each conductor and breaker must be rated for.

What is the difference between single-phase and three-phase current calculations?

Single-phase uses I = P ÷ (V × PF) — no √3 factor, because there is only one line-to-neutral circuit. Three-phase divides by √3 as well and uses the line-to-line voltage. For the same 11 kW load, single-phase at 230 V draws about 56 A while three-phase at 400 V draws only about 19 A.

Why does power factor matter when sizing cables?

Power factor below 1.0 means the apparent current is higher than the real power suggests, so a motor with PF 0.85 draws more current than a resistive load of the same kW. The calculator defaults to 0.85 for a typical motor, but you should enter the nameplate value of your actual load.

How it works

Single-phase: I = P ÷ (V × PF); three-phase: I = P ÷ (√3 × V × PF) using line-to-line voltage. HP is converted at 1 hp = 0.7457 kW. The result is the theoretical full-load current — add your local de-rating factors and service margin before choosing a rating.

← Back to all calculators

More calculators

← Back to all calculators