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Calculator · E-501

Three-phase kVA, kW & amps calculator

Convert a load between kW, kVA and amps at the voltages Calgary commercial buildings use, and see the next common transformer size.

Three-phase kVA & amps · E-501Metric · SI
kW / kVA / A
PF
An assumption unless you have a measured value. Motors and drives vary; resistive loads are near 1.0.
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Planning estimate only. Not for sizing conductors, transformers or protection for installation.

CCT 01How it works

Apparent power, current and voltage are tied together by the supply:

  • Three phase: kVA = √3 × VL-L × I ÷ 1,000, so I = kVA × 1,000 ÷ (1.732 × V).
  • Single phase: kVA = V × I ÷ 1,000.
  • Real power: kW = kVA × power factor.

At 120/208 V the line-to-line voltage is 208 V; at 347/600 V it is 600 V. The same load draws a little over a third of the current at 600 V that it draws at 208 V, which is why larger buildings distribute at 600 V. See 120/208 V vs 347/600 V.

CCT 02Assumptions and limits

  • Balanced three-phase load. Unbalanced loads put more current on the heaviest phase.
  • The transformer list is the common set of three-phase dry-type ratings used in Canadian buildings. Sizing a real transformer also considers growth, harmonics, inrush, temperature rise and the code’s rules, and is done by the designer.
  • This calculator does not size conductors or overcurrent protection.

Questions people ask

How many amps is a 75 kVA transformer at 208 V?

At 208 V three phase, 75 kVA × 1,000 ÷ (1.732 × 208) is about 208 A. Enter 75 kVA above to see it at other voltages.

What is the difference between kW and kVA?

kW is the real power that does work; kVA is what the supply and the transformer must carry. The ratio is the power factor. Equipment is rated in kVA because heating depends on current, whatever the power factor.

Why do commercial buildings use 600 V?

Lower current for the same power means smaller feeders and less voltage drop over long runs. Lighting and receptacles then run from step-down transformers at 120/208 V. Read 120/208 V vs 347/600 V.