Specification

2700DB0202R03/12 Corner-Grounded Delta (Grounded B Phase) Systems
09/2012 Voltages
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3
ENGLISH
Article 404.2 Switch Connections (A) Three- and Four-Way Switches. Three- and four-way switches shall be
wired so that all switching is done only in the ungrounded circuit
conductor. Where in metal raceways or metal-armored cables, wiring
between switches and outlets shall be in accordance with 300.20(A).
Exception: Switch loops shall not require a grounded conductor.
(B) Grounded Conductors. Switches or circuit breakers shall not disconnect
the grounded conductor of a circuit.
Exception: A switch or circuit breaker shall be permitted to disconnect a
grounded circuit conductor where all circuit conductors are disconnected
simultaneously, or where the device is arranged so that the grounded
conductor cannot be disconnected until all the ungrounded conductors
of the circuit have been disconnected.
Article 430.36 Fuses—In Which Conductor Where fuses are used for motor overload protection, a fuse shall be inserted
in each ungrounded conductor and also in the grounded conductor if the
supply system is 3-wire, 3-phase ac with one conductor grounded.
Schneider Electric adds the following clarification note to Article
430.36:
NOTE: It is prohibited to fuse the grounded conductor on service or
distribution disconnects.
Article 430.85 In Grounded Conductors One pole of the controller shall be permitted to be placed in a permanently
grounded conductor, provided the controller is designed so that the pole in
the grounded conductor cannot be opened without simultaneously opening
all conductors of the circuit.
UL Standard 67
Paragraph 12.2.3 A 2-pole circuit breaker, used in a panelboard marked for use on a
corner-grounded delta system, shall be marked “1Ø–3Ø.”
Paragraph 12.5.2 An overcurrent device shall not be connected in the permanently grounded
wire of any circuit unless opening of the overcurrent device simultaneously
opens all the conductors in that circuit.
UL Standard 891
Paragraph 8.6.11.3 A 2-pole circuit breaker intended for use on a 3-phase load shall be marked
“1Ø–3Ø” when installed in a switchboard for use on a corner grounded delta
system.
Paragraph 8.6.6.3 No overcurrent device shall be placed in any permanently grounded
conductor unless it simultaneously opens all conductors of the circuit.
UL Standard 489
Paragraph 7.1.11.3.1.4 2-pole circuit breakers are to be tested on a single-phase circuit with the
load terminals short circuited. An additional 2-pole sample shall be tested on
a 3-phase circuit if the circuit breaker is marked “1Ø–3Ø.”
Voltages
Table 1: Possible Low Voltage Corner-Grounded Delta Systems
System Voltage Phase-to-Phase Voltage Description
120 V 120 V
The ungrounded phases, generally A and C
phases, have the same phase-to-ground
voltage, while B phase is solidly grounded.
240 V 240 V
480 V 480 V
600 V 600 V