AmpSizerkVA to amps
kVA to amps
30.1 amps
from 25 kilovolt-amps at 480 V, power factor 1.00
| Also equal to | Value |
|---|---|
| Current | 30.1 A |
| Real power | 25,000 W = 25.00 kW |
| Apparent power | 25,000 VA = 25.00 kVA |
| Mechanical equivalent | 33.53 HP |
| In milliamps | 30,070 mA |
- Breaker for this as a continuous load
- 40 A
- Copper conductor that carries it
- 8 AWG
Keep the power factor at 1 for a straight kVA to amps conversion — kVA already includes it. Change it only when you want the kW figure alongside.
A sizing aid from the published NEC tables, not a design — have it signed off by a licensed electrician against the code your inspector enforces. Calculations follow the US NEC; outside the US, follow your local electrical code.
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MonthlyOne thing a month worth measuring, testing or recalculating on a home electrical system — the part of sizing that happens after the install. No product pitches, and nothing that needs a live panel.
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How do you convert kVA to amps?
The AmpSizer kVA-to-amps result for 25 kVA on a 480 volt three-phase supply is 30.1 amps. The formula is kVA × 1,000 ÷ (1.732 × volts) for three phase, and kVA × 1,000 ÷ volts for single phase.
Power factor does not belong in this conversion. kVA is apparent power — it already is volts times amps — so dividing by a power factor as well double-counts it. That is the most common mistake made with this particular formula.
Where power factor does come in is kW: 25 kVA at a power factor of 0.9 delivers 22.5 kW of real work. The transformer still has to carry all 25 kVA of current.
The transformer and generator sizes that actually exist, in amps, at the voltages they are usually connected to.
| Rating | 240 V, 1-phase | 208 V, 3-phase | 480 V, 3-phase |
|---|---|---|---|
| 5 kVA | 20.8 A | 13.9 A | 6.0 A |
| 10 kVA | 41.7 A | 27.8 A | 12.0 A |
| 15 kVA | 62.5 A | 41.6 A | 18.0 A |
| 25 kVA | 104.2 A | 69.4 A | 30.1 A |
| 45 kVA | 187.5 A | 124.9 A | 54.1 A |
| 75 kVA | 312.5 A | 208.2 A | 90.2 A |
| 112.5 kVA | 468.8 A | 312.3 A | 135.3 A |
The pattern worth internalising: at 480 V three-phase, amps are roughly 1.2 × kVA. At 208 V three-phase, amps are roughly 2.8 × kVA. Those two shortcuts cover most of commercial work.
Where the conversion goes wrong
Line voltage versus phase voltage. The 1.732 in the three-phase formula assumes you used the line-to-line voltage — 208, 480, 600. Using the line-to-neutral figure of 120 or 277 with the same formula gives an answer three times too small.
Single phase from a three-phase supply. A 120 V circuit taken from a 208 V three-phase panel is a single-phase circuit at 120 V, with no root three anywhere in it. The panel being three-phase does not make the circuit three-phase.
Assuming a power factor twice. Once in going kVA to kW, and again in going kVA to amps. Only the first one belongs there.
Frequently asked questions
How many amps is a 25 kVA transformer?
30.1 A on a 480 V three-phase primary and 60.1 A on a 240 V secondary. On single phase the same 25 kVA is 104 A at 240 V. The secondary current is always the bigger number, because the voltage went down and the power did not.
Do I divide by power factor when converting kVA to amps?
No. kVA is apparent power and already equals volts times amps, so the power factor is baked in. You use the power factor to go between kVA and kW, not between kVA and amps. Applying it twice is why people get answers that are 20% out.
Why are generators rated in kVA and not kW?
Because the alternator’s limit is current, and current comes from apparent power. A generator does not know or care what your load does with the amps — it only has to deliver them without overheating its windings. Many generators carry both ratings: a kVA figure for the alternator and a kW figure for the engine.
What size UPS do I need in kVA?
Add up the VA of the equipment, not the watts, and leave 20 to 25% headroom. Older UPS units were rated with an assumed power factor of 0.6 to 0.7, which is why a 1,000 VA unit often only delivered 600 W; modern ones with active power-factor-corrected loads are much closer to 1:1.
Is kVA always bigger than kW?
Bigger or equal, never smaller. They are equal at unity power factor, which is a resistive load. Every real installation has a power factor below 1 somewhere, so kVA is the larger figure in practice — and it is the one the wire, the breaker and the transformer are sized on.
How we calculate this
kVA × 1,000 ÷ volts; three-phase current is kVA × 1,000 ÷ (1.732 × volts),
where 1.732 is the square root of three and the voltage is line-to-line. Real power is
kVA × power factor and reactive power is the remainder in quadrature. Power factor is deliberately not
applied to the kVA-to-amps conversion itself, because apparent power already equals volts times amps.
Where a device and conductor are shown for the resulting current, the current is taken at 125%, the device
is the next standard rating in NEC 240.6(A), and the conductor satisfies Table 310.16 with 240.4(D)
applied. Transformer protection at 125% follows 450.3(B).Worked example
With Amount 25, Measured in kilovolt-amps, Convert to amps, Voltage 480 V, Supply Three phase, Power factor 1.00, this page works out 30.1 amps. from 25 kilovolt-amps at 480 V, power factor 1.00
- Breaker for this as a continuous load40 A
- Copper conductor that carries it8 AWG
Sources:
The three ratings on a nameplate
kVA — apparent power. What the supply has to deliver. Transformers, generators and UPS units are rated here, and conductors are sized from it.
kW — real power. What becomes work, heat or light. Motors are rated here, and this is what the meter bills.
kVAR — reactive power. The difference, circulating without doing anything. It is what power-factor correction capacitors cancel out, and what utilities penalise on large supplies.