Three Phase Electrical Wiring Diagram - System: Typical wiring requirements: Additional requirements: Heat pump: Wire to the condenser (outside unit) with a single-phase, 20 amp supply. • Larger units may require a 4 mm 2 /32 amp supply • Ducted or multi-evaporator systems require a three-phase supply.. King KBP2006-3MP 5700-Watt MAX 208-Volt 1 or Three Phase Paw Unit Heater - King Kbp Heater - Amazon.com. This section shows some lateral-thinking ideas using common switches and pickups. All are my own invention. Out of Phase - Series . If you have on/off switches for your pickups, you can use the off positions for out of phase on series..