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Three Phase Current – Calculation

Use this guide to size the right generator for your needs

The power taken by a circuit (single or three-phase) is measured in watts W (or kW). The product of the voltage and current is the apparent power, measured in VA (or kVA). The relationship between kVA and kW is the Power Factor (PF):

kW = kVA × PF (or) kVA = kW / PF

Single Phase System

Given the kW and power factor, the kVA can be worked out directly. The current is the kVA divided by the voltage.

Example: 23 kW load at 230V, PF 0.86 → kVA = 23/0.86 = 26.7 kVA → Current = 26,700 / 230 = 116 A

Three Phase System

In a three-phase system, convert to single-phase by dividing total kW by 3, then follow the single-phase method.

Example: 36 kW balanced load at 400V line-to-line, PF 0.86 → Single-phase power = 36/3 = 12 kW → kVA = 12/0.86 = 13.9 kVA → Current = 13,900 / 230 = 60 A

Three-Phase Current Formula

I = P / (√3 × V × PF), where P is watts, V is line voltage (380V in Saudi Arabia), PF is power factor.

Frequently Asked Questions

How do I calculate the kVA needed for my generator?

Divide the total watt load by the power factor (typically 0.8 for diesel generators), then divide by 1000 to get kVA. Multiply by 1.25 to operate at 80% prime power capacity.

What is the difference between prime power and standby power in a generator?

Prime power is the continuous maximum power available at variable load for unlimited hours. Standby power is the maximum power available during a utility outage — typically 10% higher than prime, not for continuous use.

What is the formula for three-phase current calculation?

I = P / (√3 × V × PF), where P is power in watts, V is line voltage (380V in Saudi Arabia), and PF is the power factor.

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