How many amps is a 25 kVA transformer?

Single-phase at 240 V: 25,000 ÷ 240 = 104 A. Three-phase at 208 V: 25,000 ÷ (√3 × 208) = 69 A per line.

kVA or kW for a generator?

Generators carry both: the kVA is the alternator’s current limit, the kW the engine’s. At PF 0.8 a 10 kVA set delivers 8 kW. Size on the larger of the load’s kVA and kW needs.

kVA calculator

Apparent power · single-phase24.00kVAkVA = V × I ÷ 1000240 V × 100 A

Given

Phase

Voltage

Line-to-neutral or 240

Current

Per line

Power factor

0.8 is the usual assumption for mixed motor loads

Real powerkVA × PF: 19.20 kW
Reactive power√(kVA² − kW²): 14.40 kvar
Line currentkVA × 1000 ÷ 240 V: 100.0 A
Next common transformer ratingcommon dry-type catalogue sizes, not a code table: 25 kVA

Transformers and generators are rated in kVA because heating depends on current, not on the power factor of what is plugged in. Sizing a transformer also needs the load calculation of Article 220 and the 450.3 protection table; this page is the arithmetic only.

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Transformers, generators and services are rated in kilovolt-amperes because heating follows current, not the power factor of the load. Give volts and amps, or kilowatts and a power factor, and read the kVA, the real and reactive power, the line current and the next common transformer size. Sizing a transformer also needs the Article 220 load calculation and the 450.3 protection table; this is the arithmetic.

Worked examples

240 V, 100 A single-phase: 24 kVA. At PF 0.8 that is 19.2 kW and 14.4 kvar; a 25 kVA transformer is the next standard size. Open this run
480 V, 100 A three-phase: √3 × 480 × 100 ÷ 1000 = 83.1 kVA; a 112.5 kVA three-phase transformer is the next common rating. Open this run
100 kW at PF 0.8: 125 kVA and 75 kvar. Improving the power factor to 0.95 brings the same 100 kW down to 105 kVA. Open this run
Generator: 7.5 kW at PF 0.8, 240 V: 9.4 kVA and 39 A. Most portable generators are rated in watts at PF 1; standby units in kW at 0.8. Open this run

How it is worked out

kVA = V × I ÷ 1000 (single-phase) or √3 × V × I ÷ 1000 (three-phase, V line-to-line). kVA = kW ÷ PF. kW = kVA × PF. kvar = √(kVA² − kW²). I = kVA × 1000 ÷ V or ÷ (√3 × V).

The transformer list (1 to 1000 kVA) is the common dry-type catalogue sizes, not a code table.

The figures behind it

Apparent power: S = V × I, P = S × PF, Q = √(S² − P²); arithmetic, no table.

Questions people ask

How many amps is a 25 kVA transformer?: Single-phase at 240 V: 25,000 ÷ 240 = 104 A. Three-phase at 208 V: 25,000 ÷ (√3 × 208) = 69 A per line.
kVA or kW for a generator?: Generators carry both: the kVA is the alternator’s current limit, the kW the engine’s. At PF 0.8 a 10 kVA set delivers 8 kW. Size on the larger of the load’s kVA and kW needs.

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