Specification

Corner-Grounded Delta (Grounded B Phase) Systems 2700DB0202R03/12
Standards 09/2012
© 2002–2012 Schneider Electric All Rights Reserved2
ENGLISH
Standards This section contains a list of standards that are applicable to
corner-grounded delta systems. These standards address three basic points:
1. Any 2-pole circuit breaker intended for use on corner-grounded delta
systems shall be tested and rated for such use.
2. No overcurrent device is permitted to be used to disconnect the
grounded conductor, unless this device simultaneously disconnects all
conductors of the circuit, including the ground.
3. If the system is a corner-grounded delta system and fuses will be used
for motor overload protection, a fuse must be installed in the grounded
conductor, but only at the motor controller.
NEMA Standards Publication No. PB 1
PB 1–7.7 Corner-Grounded (Grounded B Phase)
Three-Phase Delta Applications
2-pole circuit breakers intended to be installed on corner-grounded
(grounded B phase) delta systems to supply three-phase loads shall be
marked “1 phase–3 phase.”
NEMA Standards Publication No. PB 2
PB 2–7.9 Corner-Grounded (Grounded B Phase)
Three-Phase Delta Applications
2-pole circuit breakers intended to be installed on corner-grounded
(grounded B phase) delta systems to supply three-phase loads shall be
marked “1 phase–3 phase.”
National Electrical Code
®
(NEC
®
)
Article 240.85 Applications A circuit breaker with a straight voltage rating, such as 240 V or 480 V, shall
be permitted to be applied in a circuit in which the nominal voltage between
any two conductors does not exceed the circuit breaker’s voltage rating.
A 2-pole circuit breaker shall not be used for protecting a 3-phase,
corner-grounded delta circuit unless the circuit breaker is marked
1Ø–3Ø to indicate such suitability.
A circuit breaker with a slash rating, such as 120/240 V or 480Y/277 V, shall
be permitted to be applied in a solidly grounded circuit where the nominal
voltage of any conductor to ground does not exceed the lower of the two
values of the circuit breaker’s voltage rating and the nominal voltage
between any two conductors does not exceed the higher value of the circuit
breaker’s voltage rating.
Informational Note: Proper application of molded case circuit breakers on
three-phase systems, other than solidly grounded wye, particularly on corner
grounded delta systems, considers the circuit breaker’s individual pole-
interrupting capability.
Article 230.90 (B) Not in Grounded Conductor No overcurrent device shall be inserted in a grounded service conductor
except a circuit breaker that simultaneously opens all conductors of
the circuit.
Article 240.22 Grounded Conductor No overcurrent device shall be connected in series with any conductor that
is intentionally grounded, unless one of the following two conditions are met:
(1) The overcurrent device opens all conductors of the circuit, including the
grounded conductor, and is designed so that no pole can operate
independently.
(2) Where required by Articles 430.36 or 430.37 for motor overload
protection.