Chapter 1 Electrical Fundamentals Review 15 Copyright Goodheart-Willcox Co., Inc. 240 V 240 V A B C Ground Step-down transformer 120/240 V single-phase, three-wire service 240 V Goodheart-Willcox Publisher Figure 1-20. Three-phase, three-wire delta system. This system provides 240 volts and 480 volts. A step- down transformer is used to supply 120-volt service. Neutral 120 V 208 V 120 V 120 V 208 V 208 V Ground A B C Goodheart-Willcox Publisher Figure 1-21. The three-phase, four-wire wye system is the most common three-phase system.