Chapter 10 The Service Entrance
185
Copyright Goodheart-Willcox Co., Inc.
Code Alert
Section 408.3(E)
AC Phase Arrangement. Alternating-
current phase arrangement on three-phase
buses shall be A, B, C from front to back, top
to bottom, or left to right, as viewed from
the front of the switchboard or panelboard.
The B phase shall be that phase having the
higher voltage to ground on three-phase,
four-wire, delta-connected systems. (See
the NEC for the complete section)
breaker connections are the same as in three-
wire, single-phase services.
The black (hot) circuit wire goes to the circuit
breaker terminal and the white neutral circuit
wire is connected to the neutral bus bar. As
with single-phase systems, the 120-volt circuits
should be balanced or equally arranged among
the three hot buses.
Two-pole circuit breakers are also installed
in the same manner as with three-wire, single-
phase service panels. That is, the double-pole
breaker is attached to any two of the three hot
bus bars. Again, carefully balance these between
all the buses. These comprise the two-wire,
single-phase, 208-volt circuits.
Grounded conductor
(neutral)
Three-phase
208 V circuit
Three-phase
120/208 V circuit
Neutral bus bar
Bond to cabinet
Enclosure
cabinet
Single-phase 120 V circuit
Single-phase 208 V circuit
Single-phase
120/208 V circuit
3 pole
main
breaker
N
N
Figure 10-36. Main breaker and panel circuit connections for a wye-connected three-phase, four-wire service. Hot
bus bars are marked A, B, and C.