Understanding 3-Phase Utility Power
Open Delta High Leg 240V 3-Phase
Quite often in rural areas, farms and small businesses are supplied with only 240-Volt/120-Volt single phase. A single transformer supplies this with a center tap – thus yielding 2 120-volt connections and 1 240-volt connection. The addition of only one more transformer and utility phase yields a 3-Phase system called Open Delta. This provides motors and 3-Phase line-to-line loads with 3-Phase power, but it has that one extra phase wire yielding 208 Volts to the center tap of the 120-volt/240-volt transformer. This requires caution and special wiring to prevent that “High” leg from being connected to a 120-volt load.