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kVA to Amps Conversion
Converting kVA to amperes is one of the most common calculations in electrical engineering and is essential for properly sizing conductors, breakers, and protective devices. The conversion depends on whether the system is single-phase or three-phase, and requires knowing the system voltage.
Electrical equipment such as transformers, generators, and UPS systems are typically rated in kVA. However, wire sizing, fuse selection, and circuit breaker ratings are based on current in amperes. Accurately converting between these units ensures safe and code-compliant electrical installations.
Conversion Formulas
Where I is current in amperes, kVA is apparent power in kilovolt-amperes, V is line voltage (line-to-line for 3-phase), and sqrt(3) approximately equals 1.732.
Quick Reference Table (3-Phase)
| kVA | 208V | 240V | 480V | 600V |
|---|---|---|---|---|
| 15 | 41.6 A | 36.1 A | 18.0 A | 14.4 A |
| 30 | 83.3 A | 72.2 A | 36.1 A | 28.9 A |
| 50 | 138.8 A | 120.3 A | 60.1 A | 48.1 A |
| 75 | 208.2 A | 180.4 A | 90.2 A | 72.2 A |
| 100 | 277.6 A | 240.6 A | 120.3 A | 96.2 A |
| 500 | 1388 A | 1203 A | 601 A | 481 A |
Wire Sizing Guide
- Up to 20 A: 12 AWG copper (20A breaker)
- 21-30 A: 10 AWG copper (30A breaker)
- 31-60 A: 6 AWG copper (60A breaker)
- 61-100 A: 3 AWG copper (100A breaker)
- 101-200 A: 3/0 AWG copper (200A breaker)
- Always verify with NEC tables and local codes for specific installation conditions.
Frequently Asked Questions
Why is sqrt(3) used for three-phase calculations?
In a balanced three-phase system, the three voltage phases are 120 degrees apart. The relationship between line voltage and phase voltage involves sqrt(3) = 1.732. This factor appears because power in a three-phase system is the sum of power in three single-phase circuits, and the vector relationship between line and phase quantities introduces the sqrt(3) factor.
Should I use line-to-line or line-to-neutral voltage?
For three-phase calculations, always use line-to-line voltage (e.g., 480V, not 277V). For single-phase calculations, use the voltage at which the load operates. In a 480V three-phase system, single-phase loads between a line and neutral operate at 277V.
How do I account for derating and safety margins?
The NEC requires that conductors be sized for 125% of the continuous load current. For example, if your calculated current is 80A, you need conductors rated for at least 100A. Additionally, apply derating factors for ambient temperature, conduit fill, and altitude as required by NEC Article 310.