To convert kVA to amps, divide the apparent power (kVA × 1000) by the system voltage for single-phase, or by the voltage multiplied by √3 (1.732) for three-phase. For example, a 50 kVA transformer on a 480V three-phase system delivers a full-load current of 60.1 amps. Below is the complete kVA to amp conversion chart based on nominal voltages defined in IEC 60038 and standard North American NEC configurations.
The Master kVA to Amp Conversion Chart
This table provides the baseline full-load amperage (FLA) for common transformer and generator kVA ratings. How to read this table: The values assume a unity power factor (1.0) and represent apparent power. Locate your equipment's kVA rating in the first column, then move horizontally to the column matching your installation's nominal voltage. The most frequently queried commercial transformer sizes (45 kVA, 75 kVA, and 150 kVA) are highlighted for quick bookmarking.
Source Standards: Nominal voltages align with IEC 60038 standard voltage definitions and NFPA 70 (NEC) Article 220 for branch and feeder load calculation baselines.
| Transformer / Load Size (kVA) | 1-Phase 120V (Amps) | 1-Phase 240V (Amps) | 3-Phase 208V (Amps) | 3-Phase 480V (Amps) |
|---|---|---|---|---|
| 1 kVA | 8.33 | 4.17 | 2.78 | 1.20 |
| 5 kVA | 41.67 | 20.83 | 13.88 | 6.01 |
| 15 kVA | 125.00 | 62.50 | 41.64 | 18.04 |
| 30 kVA | 250.00 | 125.00 | 83.27 | 36.08 |
| 45 kVA (Quick Jump) | — | 187.50 | 124.90 | 54.13 |
| 75 kVA (Quick Jump) | — | 312.50 | 208.18 | 90.21 |
| 100 kVA | — | 416.67 | 277.58 | 120.28 |
| 150 kVA (Quick Jump) | — | — | 416.37 | 180.42 |
| 300 kVA | — | — | 832.74 | 360.84 |
| 500 kVA | — | — | 1387.90 | 601.40 |
• 1-Phase 120V / 240V: Standard North American residential, small commercial, and light agricultural services.
• 3-Phase 208V: Common in North American commercial buildings, strip malls, and office spaces (derived from a 120/208V Wye secondary).
• 3-Phase 480V: The standard for North American industrial plants, manufacturing floors, and heavy HVAC equipment.
Applying NEC Derating and Continuous Load Rules
The baseline amperage values in the chart above represent the exact mathematical conversion of apparent power. However, you cannot size a breaker or conductor using these raw numbers alone. The National Electrical Code (NEC) requires you to apply derating multipliers based on the duty cycle of the load and the ambient temperature of the installation environment.
How derating rows modify the base value: If the kVA load is considered "continuous" (expected to run at maximum current for 3 hours or more), NEC Article 210.20(A) and 215.3 mandate that the overcurrent protection device and conductor ampacity be sized at 125% of the base calculated load. Furthermore, if your THHN/XHHW copper conductors are installed in an environment exceeding 30°C (86°F), you must apply temperature correction factors from NEC Table 310.15(B)(16).
| Load Condition | NEC Reference | Multiplier | Example: 75 kVA at 480V 3P (Base 90.2A) |
|---|---|---|---|
| Non-Continuous Load | Base Calculation | 1.00× | 90.2A (Size for 90A+ breaker) |
| Continuous Load (3+ Hours) | 210.20(A) / 215.3 | 1.25× | 112.75A (Requires 125A breaker) |
| Ambient Temp 41-45°C (75°C Column) | 310.15(B)(16) | 0.82× | Conductor ampacity must be divided by 0.82 |
| 4 Current-Carrying Conductors in Raceway | 310.15(C)(1) | 0.80× | Conductor ampacity must be divided by 0.80 |
Worked Numeric Example: You are sizing the secondary feeder for a 75 kVA, 480V three-phase transformer powering a continuous-duty manufacturing panel. The base current from the master chart is 90.21A. Because the load is continuous, you multiply 90.21A by 1.25, yielding 112.76A. You must select a standard breaker size of 125A (per NEC 240.6) and size your copper conductors to safely carry at least 112.76A after all ambient and bundling derating factors are applied (typically requiring 1 AWG THHN copper in a standard 30°C environment).
What This Table Cannot Tell You (Edge Cases & Limits)
While a kVA to amp conversion chart is the mandatory first step for load calculations, relying on it blindly will result in undersized equipment if you ignore the physical realities of your specific loads. Here is what the baseline math omits:
- Power Factor (PF) and Real Power: kVA measures apparent power. If you are calculating the actual work being done (kW), or sizing a generator that is limited by real power, you must account for power factor. A 100 kVA load with a 0.80 lagging power factor (common in induction motors) draws the same 120.3A at 480V as a resistive heater, but only delivers 80 kW of real work. For deep diagnostics on this, refer to Fluke's power factor field guides.
- Motor Inrush and Locked Rotor Amps (LRA): The chart assumes steady-state operation. A 50 kVA three-phase motor load will draw 60.1A at full load, but its starting inrush current (LRA) can be 6 to 8 times higher (up to 480A) for several seconds. Breakers must be sized with magnetic trip curves (like HMS or time-delay fuses) to tolerate this inrush without nuisance tripping, a factor entirely invisible to a steady-state kVA chart.
- Voltage Drop Over Distance: The chart assumes nominal voltage at the point of measurement. If your 480V feeder runs 400 feet from the transformer to the panel, voltage drop will reduce the actual voltage at the load. Since $Amps = \frac{kVA}{Voltage}$, a lower voltage at the load end actually forces the equipment to draw higher current to maintain the same kVA output, compounding heat and requiring upsized conductors beyond the baseline NEC 310.16 ampacity tables.
- Harmonic Distortion: In modern commercial buildings heavily populated with Variable Frequency Drives (VFDs), LED drivers, and IT server racks, non-linear loads generate triplen harmonics. These harmonics do not show up in standard kVA calculations but cause severe overheating in the neutral conductor and transformer cores. This requires specifying K-rated transformers (e.g., K-4 or K-13) and upsizing the neutral conductor to 200% of the phase conductor ampacity.
Use this chart to establish your baseline full-load amperage, then immediately apply your continuous load multipliers, ambient temperature corrections, and voltage drop calculations before finalizing your bill of materials.
