15 kVA converts to 62.5 amps at 240V single-phase, 65.2 amps at 230V single-phase, 125 amps at 120V single-phase, and 36.1 amps at 240V three-phase. The exact amperage depends entirely on your system voltage and phase configuration. Because kVA measures apparent power, this conversion does not require a power factor (PF) assumption—unlike kW conversions.
The Core Formulas (With Values Substituted)
To find the current (I) in amps from apparent power (S) in kilovolt-amps, you multiply the kVA by 1,000 to get volt-amps, then divide by the system voltage. For three-phase systems, you must also divide by the square root of 3 (approximately 1.732).
Single-Phase Calculation
The formula for single-phase AC is:
I = (kVA × 1000) / V
Substituting 15 kVA at a standard US 240V residential supply:
I = (15 × 1000) / 240I = 15,000 / 240- I = 62.5 Amps
Three-Phase Calculation
The formula for three-phase AC is:
I = (kVA × 1000) / (√3 × V)
Substituting 15 kVA at a standard US 240V three-phase industrial supply:
I = 15,000 / (1.732 × 240)I = 15,000 / 415.68- I = 36.08 Amps
1.732 × 400 = 692.8. Dividing 15,000 by 692.8 yields 21.65 Amps. Always verify your regional nominal voltage before sizing wire.
Neighboring Values Chart (12 kVA to 18 kVA)
Equipment rarely lands on an exact integer, and transformer nameplates often sit in the 12 to 18 kVA range. Use this reference table to quickly find amperage across common global voltages without recalculating.
| kVA Rating | 120V (1Ø) | 230V (1Ø) | 240V (1Ø) | 208V (3Ø) | 400V (3Ø) | 480V (3Ø) |
|---|---|---|---|---|---|---|
| 12 kVA | 100.0 A | 52.2 A | 50.0 A | 33.3 A | 17.3 A | 14.4 A |
| 13 kVA | 108.3 A | 56.5 A | 54.2 A | 36.1 A | 18.8 A | 15.6 A |
| 14 kVA | 116.7 A | 60.9 A | 58.3 A | 38.9 A | 20.2 A | 16.8 A |
| 15 kVA | 125.0 A | 65.2 A | 62.5 A | 41.6 A | 21.7 A | 18.0 A |
| 16 kVA | 133.3 A | 69.6 A | 66.7 A | 44.4 A | 23.1 A | 19.2 A |
| 17 kVA | 141.7 A | 73.9 A | 70.8 A | 47.2 A | 24.5 A | 20.5 A |
| 18 kVA | 150.0 A | 78.3 A | 75.0 A | 50.0 A | 26.0 A | 21.7 A |
Critical Assumptions: Voltage, Phase, and the Power Factor Trap
The numbers above are fixed by two assumptions: system voltage and phase configuration. If you change either, the amperage shifts drastically. Dropping from a 240V 1Ø supply to a 120V 1Ø supply doubles the current draw for the same 15 kVA load, which is why high-draw appliances like HVAC compressors and EV chargers are wired for 240V—to keep amperage (and required wire gauge) down.
When is this conversion meaningless?
Converting kVA to amps is always mathematically valid as long as you know the voltage and phase. However, the conversion becomes meaningless if your equipment nameplate actually specifies kW (kilowatts) instead of kVA, and you do not know the Power Factor (PF).
kVA is apparent power (the total power supplied by the utility). kW is real power (the power actually doing work). According to Fluke's electrical measurement guidelines, the relationship is kW = kVA × PF. If a motor nameplate reads 15 kW, you must multiply by 1,000 and divide by both voltage and PF. A 15 kW motor at 0.85 PF draws significantly more apparent current than a 15 kW resistive heater at 1.0 PF. Always double-check the 'W' versus 'VA' on the stamp plate before sizing your breakers.
Frequently Asked Questions
How many amps is a 15 kVA transformer secondary?
It depends on the transformer's winding configuration. A very common commercial setup is a 15 kVA step-down transformer (480V Delta primary to 120/208V Wye secondary). On the secondary side, the three-phase 208V output delivers 41.6 amps per phase. However, if you are pulling single-phase 120V line-to-neutral loads from that same secondary, each leg can safely supply up to 125 amps (15,000 VA / 120V), provided the total load across all three legs remains balanced and does not exceed the 15 kVA total capacity.
What size breaker and wire do I need for a continuous 15 kVA load?
Under NEC Article 210.20 and 215.3, continuous loads (those expected to run for 3 hours or more) require the overcurrent protective device to be sized at 125% of the calculated load.
For a 15 kVA load at 240V single-phase (62.5 amps): 62.5A × 1.25 = 78.12A.
You must round up to the next standard breaker size, which is 80 amps. For wire sizing, checking the 75°C column of NEC Table 310.16, you would need 4 AWG THHN copper wire (rated for 85A) or 3 AWG to safely handle the 80A breaker without violating termination temperature limits. Always verify these calculations with your local Authority Having Jurisdiction (AHJ), as local amendments may require stricter derating for ambient temperatures or conduit fill.
Why does my 15 kVA diesel generator only output 12 kW?
This is standard industry practice, not a defect. Most commercial diesel generators are rated at a 0.8 Power Factor. Because generators must supply both real power (kW) and reactive power (kVAR) to handle inductive loads like motors, the manufacturer limits the real power output to 80% of the apparent power (kVA) rating. Therefore, a 15 kVA generator × 0.8 PF = 12 kW of usable real power. If you attempt to pull 15 kW of pure resistive heating load from it, you will overload the prime mover (the engine), even if the alternator's electrical windings haven't reached their thermal limit.
