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
Example: 18,000W ÷ 240V = 75A
Example: 60A ⨯ 480V = 28,800W
3-Phase
Example: 18,000W ÷ 240V = 75 ÷ 1.73 = 43.35 A
Example: 60A ⨯ 480V ⨯ 1.73 = 49,824W