From the link Sven posted:
Electrical Requirements
15 OR 20 Ampere, 120 Volts, 60 Hertz (1/second). AC-ONLY. USE COPPER WIRE ONLY. A FOUR-WIRE OR THREE-WIRE, SINGLE PHASE ELECTRICAL SUPPLY REQUIRED. A TIME-DELAY FUSE OR CIRCUIT BREAKER AND SEPARATE CIRCUIT IS RECOMMENDED
I don't get it. What does a 4 wire 1Ø 120 Volt circuit look like?
