Basic Type of AC Power Systems
Types
Single Phase
120/240 volt, 1 phase, 3 wire Application
Any load up to 400 A, then
should consider 3 phase.
Motors 7.5 HP maximum.
Most equipment available 120-
240-Volt. This is the most
standard system.
Individual unit heaters are
limited to about 10 KW max.
Three Phase Three Phase
120/208 V, WYE, 3 phase, 4 wire Any application from 200A up,
allows motors larger than 7.5 HP
and has 120 volts available from
all legs to neutral. Must have 208
Volt rated motors and heaters.
Easy to balance 120 Volt loads
From each phase to neutral.
240 Volt heaters used on 208V
will supply only 75% of heat.
All three phase systems provide
1.73 times as much power as a
single phase system of same
120 V, 1 phase, 208V 1 phase and ampacity for only about 1.25%
3 phase loads can be used. the cost.
More economical.
All panel spaces can be used.
No wild leg.
6/20/02 Chapter 2: Basic Types of Ac Power Systems 1/3
