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Convert apparent power in kilovolt-amperes (kVA) to electrical current in amperes (A). Calculate amps for single-phase and three-phase electrical systems.
Common voltages: 120V, 208V, 240V, 277V, 480V, 600V
A = (kVA × 1000) ÷ V
Amps equals kVA times 1000 divided by volts
A = (kVA × 1000) ÷ (√3 × V)
√3 ≈ 1.732 for three-phase calculations
| kVA | Amps @ 120V | Amps @ 208V | Amps @ 240V | Amps @ 480V |
|---|---|---|---|---|
| 5 kVA | 41.67 A | 24.04 A | 20.83 A | 10.42 A |
| 10 kVA | 83.33 A | 48.08 A | 41.67 A | 20.83 A |
| 15 kVA | 125.00 A | 72.12 A | 62.50 A | 31.25 A |
| 25 kVA | 208.33 A | 120.19 A | 104.17 A | 52.08 A |
| 50 kVA | 416.67 A | 240.38 A | 208.33 A | 104.17 A |
| 75 kVA | 625.00 A | 360.58 A | 312.50 A | 156.25 A |
| 100 kVA | 833.33 A | 480.77 A | 416.67 A | 208.33 A |
| kVA | Amps @ 208V | Amps @ 240V | Amps @ 480V | Amps @ 600V |
|---|---|---|---|---|
| 15 kVA | 41.65 A | 36.08 A | 18.04 A | 14.43 A |
| 25 kVA | 69.42 A | 60.14 A | 30.07 A | 24.06 A |
| 50 kVA | 138.84 A | 120.28 A | 60.14 A | 48.11 A |
| 75 kVA | 208.25 A | 180.42 A | 90.21 A | 72.17 A |
| 100 kVA | 277.67 A | 240.56 A | 120.28 A | 96.23 A |
| 150 kVA | 416.50 A | 360.84 A | 180.42 A | 144.34 A |
| 200 kVA | 555.33 A | 481.13 A | 240.56 A | 192.45 A |
| 500 kVA | 1388.34 A | 1202.81 A | 601.41 A | 481.13 A |
kVA to amps conversion translates apparent power measured in kilovolt-amperes into electrical current measured in amperes. While transformers, generators, and UPS systems are rated in kVA to describe their total power capacity, the physical components that carry electricity — wires, breakers, busbars, and switches — are all rated in amps. This conversion is therefore a fundamental step in electrical system design. The calculation depends on the system voltage and whether the circuit is single-phase or three-phase, because higher voltages carry the same power at lower current levels. Electricians, engineers, and facility managers use this conversion daily when sizing conductors, selecting overcurrent protection devices, and verifying that existing infrastructure can handle new loads.
Find the kVA rating on the equipment nameplate. Transformers, generators, and UPS systems always display their kVA capacity. This represents the total apparent power the device can deliver.
Note the operating voltage of the circuit. Common single-phase voltages include 120V and 240V. Common three-phase voltages include 208V, 240V, 480V, and 600V. Use the line-to-line voltage for three-phase calculations.
For single-phase: A = (kVA × 1000) ÷ V. For three-phase: A = (kVA × 1000) ÷ (√3 × V). The √3 factor (approximately 1.732) accounts for the phase relationship in three-phase systems.
After calculating amps, select conductors and breakers rated for the calculated current. For continuous loads, multiply by 1.25 per NEC requirements. Choose the next standard breaker size above the calculated value.
Conductors and breakers rated in amps must match the actual current flowing through them. An undersized wire carrying too many amps overheats, degrades insulation, and can start fires. Accurate kVA to amps conversion is the first step to a safe installation.
The amperage determines the minimum conductor gauge (AWG or kcmil) needed for a circuit. Getting this calculation wrong means either paying for oversized copper or risking dangerous overloading of undersized conductors.
The National Electrical Code (NEC) and local regulations require that all circuits be properly protected. Inspectors verify that breaker ratings match calculated loads. Incorrect kVA to amps conversion leads to code violations and failed inspections.
| Transformer kVA | 1φ 240V | 3φ 208V | 3φ 480V |
|---|---|---|---|
| 15 | 62.5 A | 41.6 A | 18.0 A |
| 25 | 104.2 A | 69.4 A | 30.1 A |
| 45 | 187.5 A | 124.9 A | 54.1 A |
| 75 | 312.5 A | 208.3 A | 90.2 A |
| 112.5 | 468.8 A | 312.4 A | 135.3 A |
| 150 | 625.0 A | 416.5 A | 180.4 A |
| 300 | 1250.0 A | 833.0 A | 360.8 A |
| 500 | 2083.3 A | 1388.3 A | 601.4 A |
| 750 | 3125.0 A | 2082.5 A | 902.1 A |
| 1000 | 4166.7 A | 2776.7 A | 1202.8 A |
Current and voltage are inversely related for a given kVA rating. Doubling the voltage halves the current. This is why higher voltage systems (480V, 600V) use significantly smaller wires and breakers than lower voltage systems (120V, 208V) for the same kVA load. A 100 kVA load draws 833 amps at 120V but only 120 amps at 480V three-phase.
Use the formula: Amps = (kVA × 1000) ÷ (1.732 × Voltage). For a 500 kVA transformer at 480V: Amps = (500 × 1000) ÷ (1.732 × 480) = 601.4 amps per phase. This is the current each phase conductor must carry, so size your wires and breakers accordingly.
It depends on which side of the transformer you are sizing components for. Use the primary voltage to calculate primary-side breakers and wiring, and the secondary voltage for secondary-side components. The kVA rating remains the same on both sides, but the amps will differ because the voltages are different.
Power factor does not directly change the kVA-to-amps math since kVA already includes both real and reactive power. However, poor power factor increases the kVA needed for a given real power (kW) load, which in turn increases the amps. Improving power factor reduces kVA and therefore reduces current, allowing smaller conductors.
Size conductors and protective devices for 125% of the calculated continuous load current per NEC Article 215. Additionally, consider reserving 20-30% spare capacity in panels and transformers for future expansion. This practice avoids costly re-wiring when new equipment is added to the system.