ANSI C84.1
NOTES FOR TABLE 17
(a) Three-phase, three-wire systems are systems in which only the three-phase conductors are carried out from the source
for connection of loads. The source may be derived from any type of three-phase transformer connection, grounded
or ungrounded. Three-phase, four-wire systems in which a grounded neutral conductor is also carried out from the
source for connection of loads. Four-wire systems in this table are designated by the phase-to-phase voltage,
followed by the letter Y (except for the 240/120 V delta system), a slant line, and the phase-to-neutral voltage.
Single-phase services and loads may be supplied from either single-phase or three-phase systems. The principal
transformer connections that are used to supply single-phase and three-phase systems are illustrated in Fig 3.
IEEE 241
The nominal system voltages in Table 17 are designated in the same way as the designation on the nameplate of the
transformer for the winding or windings supplying the system.
1) Single-Phase Systems 120 V - Indicates a single-phase, two-wire system in which the nominal voltage
between the two wires is 120 V.
120/240 V - Indicates a single-phase, three-wire system in which the nominal voltage between the two
phase conductors is 240 V, and from each phase conductor to the neutral is 120 V.
2) Three-Phase Systems 240/120 V - Indicates a three-phase, four-wire system supplied from a delta
connected transformer. The midtap of one winding is connected to a neutral. The three phase conductors
provide a nominal 240 V three-phase, three-wire system, and the neutral and two adjacent phase conductors
provide a nominal 120/240 V single-phase, three-wire system.
Single number - Indicates a three-phase, three-wire system in which the number designates the nominal
voltage between phases.
Two numbers separated by Y/ - Indicates a three-phase, four-wire system from a wye-connected
transformer in which the Þrst number indicates the nominal phase-to-phase voltage and the second the
nominal phase-to-neutral voltage.
NOTES
1) All single-phase systems and all three-phase, four-wire systems are suitable for the connection of phase-to-neutral load.
(2) See Chapter 4 for methods of system grounding.
(3) See Fig 3 for transformer connections.
