16 Modern Commercial Wiring Copyright Goodheart-Willcox Co., Inc. There are other system confi gurations used for both commercial and industrial applica- tions. However, they are essentially derived from these fi ve basic types. Phase is represented by the Greek letter ϕ, wire is abbreviated with a w, and a wye system is designated with a Y. For example, a three- phase, four-wire 120/208-volt wye system is abbreviated as 3ϕ, 208 Y/120 V, 4 w. 1.4.1 Voltage Standards Nominal voltage indicates a desired level of the supply voltage for the electrical system. Rated voltage is the preferred voltage for equipment, particularly motors. Commercial electrical systems are within the category of low and medium voltage high voltage is reserved for power company distribution systems. The table in Figure 1-24 lists the nominal and rated voltages for low and medium voltage categories as issued by the American National Standards Institute (ANSI). Neutral 277 V 480 V 277 V 277 V 480 V 480 V Ground A B C Goodheart-Willcox Publisher Figure 1-22. A three-phase, four-wire, 480/277-volt wye system is similar to the 120/208-volt, four-wire wye system. 120 V 240 V 120 V 240 V 240 V 208 V Neutral High leg B C A Goodheart-Willcox Publisher Figure 1-23. The three-phase, four-wire delta system is a modified three-wire delta system. A grounded neutral wire is connected to one of the secondary transformer windings. Goodheart-Willcox Publisher Figure 1-24. This table lists nominal voltage, rated voltage, and general voltage class of standard supply systems. Nominal Voltages for Commercial Electrical Systems Nominal Voltage Rated Voltage (Motor Rating) General Voltage Class Low Voltage 1Φ, 120/240 V, 3 w 115/230 V 125/250 V 3Φ Electrical Sytems 208 Y/120 V, 4 w 200 V 125/250 V 240 V, 3 w 230 V 250 V 480 Y/277 V, 4 w 460 V 600 V 480 V, 3 w 460 V 600 V 600 V, 3 w 575 V 600 V Medium Voltage 2400 V, 3 w 2300 V 5 kV 4160 Y/2400 V, 4 w 4000 V 5 kV 4160 V, 3 w 4000 V 5 kV 4800 V, 3 w 4600 V 5 kV 6900 V, 3 w 6600 V 15 kV 13800 Y/7970 V, 4 w 13200 V 15 kV 13800 V, 3 w 13200 V 15 kV