When selecting the correct sized SCR power controller, rate the SCR for at least 110% of the heater load. Heaters and power lines have tolerances that can swing on any given day or location.
Single Phase
| Watts | ÷ | Volts | = | Amps |
| ÷ |
Example: 18,000W ÷ 240V = 75A
| Amps | ⨯ | Volts | = | Watts |
| ⨯ |
Example: 60A ⨯ 480V = 28,800W
3-Phase
| Watts | ÷ | Volts | ÷ | 1.73 | = | Amps |
| ÷ | ÷ | 1.73 |
Example: 18,000W ÷ 240V = 75 ÷ 1.73 = 43.35 A
| Amps | ⨯ | Volts | ⨯ | 1.73 | = | Watts |
| ⨯ | ⨯ | 1.73 |
Example: 60A ⨯ 480V ⨯ 1.73 = 49,824W