kW and kVA to Amps
With rating 10 kW or kVA, voltage 400 V, power factor 0.8, kw and kva to amps comes to 18.0 A — amps. It is reached in 4 steps, the last of which is 12.5 * 1000 / (400 * 1.7320508), and each one is printed on the page with its numbers filled in. The formula is the one published by IEEE Std 141, not an approximation fitted to it.
Current drawn by a load rated in kW or kVA, on any voltage and phase. The unit on the nameplate decides whether power factor enters the sum.
Formula and sources checked · How we check
Nameplate is in kW — real power, Rating 10 kW or kVA, Voltage 400 V, Supply AC three phase — line-to-line voltage
18.0 A
Amps for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.
It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.
- Apparent power
0 * 10 + 1 * (10 / 0.8)12.5 kVA- Real power
1 * 10 + 0 * (10 * 0.8)10 kW- Current
12.5 * 1000 / (400 * 1.7320508)18.042 A- Reactive power
sqrt(abs(12.5 * 12.5 - 10 * 10))7.5 kVAr
Worked example
A 10 kW three-phase motor at 0.8 power factor draws 18.0 A, not the 14.4 A a power-factor-free sum gives. The extra 25% is reactive current the motor returns to the supply every cycle and the cable still has to carry.
How to work it out yourself
- 1.Read the nameplate unit before anything else. kW is real power and kVA is apparent power, and confusing them is a 25% error at a typical power factor — always in the direction of undersizing.
- 2.Use the line-to-line voltage for three phase. That is what a plate marked 400 V or 480 V means; the line-to-neutral 230 V or 277 V is a different number and gives an answer √3 too large.
- 3.Take the power factor from the nameplate where there is one. Generator sets are rated at 0.8 by convention, so a 100 kVA set is an 80 kW set.
- 4.The reactive line is what a capacitor bank would have to supply to correct the load to unity — the size of the correction problem, in kVAr.
Generator kVA to amps, 400 V three phase
| Rating (kW or kVA) | Amps | Real power |
|---|---|---|
| 5 | 9.0 A | 5 kW |
| 7.5 | 13.5 A | 7.5 kW |
| 10 | 18.0 A | 10 kW |
| 15 | 27.1 A | 15 kW |
| 20 | 36.1 A | 20 kW |
| 30 | 54.1 A | 30 kW |
| 40 | 72.2 A | 40 kW |
| 50 | 90.2 A | 50 kW |
| 60 | 108.3 A | 60 kW |
| 75 | 135.3 A | 75 kW |
| 100 | 180.4 A | 100 kW |
Generators are rated in kVA at a power factor of 0.8, so the usable real power is 80% of the plate figure: a 100 kVA set delivers 80 kW.
The formula
- Apparent power
0 * 10 + 1 * (10 / 0.8) - Real power
1 * 10 + 0 * (10 * 0.8) - Current
12.5 * 1000 / (400 * 1.7320508) - Reactive power
sqrt(abs(12.5 * 12.5 - 10 * 10))
Source: IEEE Std 141 — three-phase power relationships, 10 CFR 431 Subpart B — federal efficiency standards and nameplate data for electric motors, NFPA 70 (NEC) Article 430 — motor circuit conductors and full-load current tables
Questions people actually ask
- How do you convert kW to amps on three phase?
- Amps = kW × 1000 ÷ (volts × power factor × 1.732). At 400 V and 0.8 PF, 10 kW is 18.0 A. Leaving the power factor out gives 14.4 A and undersizes the cable by a quarter.
- What is the difference between kW and kVA?
- kVA is what the supply carries, kW is what the load converts to work. They are equal only at a power factor of 1. A generator rated 100 kVA at 0.8 PF delivers 80 kW, and connecting an 100 kW load to it overloads the alternator even though the "power" figures look compatible.
- Why are generators rated in kVA?
- Because the alternator windings and the cabling are limited by current, and current follows apparent power. The engine is limited by real power. Rating the set in kVA at an assumed 0.8 power factor states the electrical limit, which is the one that burns something out.
- What is kVAr?
- Reactive power — the part that shuttles between the supply and the load's magnetic fields without doing work. It is the third side of the triangle: kVA² = kW² + kVAr². Utilities charge large customers for it, and a capacitor bank sized in kVAr is how it is cancelled.
- Is motor full-load current the same as this?
- Close, but the NEC requires conductors to be sized from the tables in Article 430 rather than from a nameplate calculation. Those table values are deliberately conservative. Use this for sizing decisions and the code tables for anything being inspected.
Related
- Watts to AmpsWatts to amps and back, with the power factor and the phase that AC needs. A DC answer applied to a 3-phase motor is out by 73%.
- Voltage Drop CalculatorVoltage lost along a copper or aluminium run, as volts and as a percentage, against the 3% the NEC recommends for a branch circuit.
- Ohm's Law CalculatorVoltage, current, resistance and power from any two of them, with the whole set printed rather than the one you asked for.
- Resistor Colour Code CalculatorResistance and tolerance from the bands on a resistor, with the E-series value it is meant to be.
- Volts to WattsVolts alone do not give watts — one more quantity is required. Enter amps, ohms or the wattage and this gives the rest of the set.
- mAh to WhBattery capacity in mAh converted to watt-hours, which is the only figure two batteries at different voltages can be compared on — and the one airlines limit.
Put this calculator on your site
Free, no attribution required beyond the link.
<iframe src="https://rulecalculators.com/embed/kw-to-amps" width="100%" height="420" style="border:1px solid #e7e4de;border-radius:12px" title="kW and kVA to Amps"></iframe>