Specification

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Data Bulletin

2700DB0202R03/12

09/2012

Replaces 2700DB0202R2/09 dated 02/2009

Corner-Grounded Delta (Grounded B Phase) Systems

Class 2700

Retain for future use.

™

ENGLISH

Introduction Corner-grounded delta systems are not recommended for new installations.

However, some utilities still provide this system, and many old installations

still exist. Schneider Electric has tested equipment for use on

corner-grounded delta systems to provide Underwriters Laboratories Inc.

(UL

) listed products for this application.

This document outlines the background of corner-grounded delta systems

and lists the equipment rated for use on these systems.

Background In the past, delta-delta connected transformers were extensively used in

electrical distribution systems. With this type of system, it was practical to

continue distributing three-phase power while performing maintenance on one

unit of the three-phase transformer bank. Now, with the advent of more reliable

modern transformers and the popularity of three-phase units, the delta-delta

connected transformer no longer has the advantage it had in the past.

One of the disadvantages of the delta-delta system is the absence of an

intentional connection to ground on the transformer secondary. To obtain a

grounded system, one of the corners of the delta secondary is grounded.

With decreased usage of the delta-delta connected transformer and

increased usage of delta-wye connected transformers, the corner-grounded

delta is rarely applied in modern systems.

Definitions

Corner-Grounded Delta System A system in which the transformer secondary is delta-connected with one

corner of the delta solidly grounded. Corner-grounded delta systems are

also referred to as grounded B phase systems, grounded phase services,

and end-grounded delta systems.

Ungrounded System A system without an intentional connection to ground, except through

potential indicating or measuring devices.

Grounded System A system that has at least one conductor or point intentionally connected to

ground, either solidly or through an impedance.

Solidly Grounded An intentional connection made directly to ground without inserting any

resistor or impedance.

Figure 1: System Diagram, 3Ø3W Ground BØ Delta

Summary of content (8 pages)

PAGE 1
2700DB0202R03/12 09/2012 Data Bulletin ENGLISH Replaces 2700DB0202R2/09 dated 02/2009 Corner-Grounded Delta (Grounded B Phase) Systems Class 2700 Retain for future use. Introduction Corner-grounded delta systems are not recommended for new installations. However, some utilities still provide this system, and many old installations still exist. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc.
PAGE 2
Corner-Grounded Delta (Grounded B Phase) Systems Standards Standards 2700DB0202R03/12 09/2012 ENGLISH 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.
PAGE 3
Article 404.2 Switch Connections Corner-Grounded Delta (Grounded B Phase) Systems Voltages (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.
PAGE 4
Corner-Grounded Delta (Grounded B Phase) Systems Theory Theory 2700DB0202R03/12 09/2012 A corner-grounded delta system has the following characteristics: ENGLISH • Grounding one phase stabilizes the voltage of the other two phases to ground. • High fault currents may flow on the first ground fault, requiring the immediate clearance of this first fault. • The voltage to ground in this system will be the system voltage, usually 240 or 480 volts.
PAGE 5
Application Corner-Grounded Delta (Grounded B Phase) Systems Application Schneider Electric has tested and obtained a UL listing for equipment to be used on grounded B phase systems. The “Devices” section below lists devices on unassembled and factory assembled distribution equipment that is suitable for such use.
PAGE 6
Corner-Grounded Delta (Grounded B Phase) Systems Devices Safety Switches ENGLISH Table 4: Table 4 lists 2-pole safety switches that are UL Listed for use on 240 and 480 Vac grounded B phase systems. Refer to the Digest, CAD drawings, or device wiring diagram(s) for complete information. Safety Switches Safety Switches Ampere Rating System Voltage (VAC) 30 General Duty 2700DB0202R03/12 09/2012 Type Construction Short Circuit Rating 10,000 A 60 100 NEMA Types 120 240 Neutral installed e.g.
PAGE 7
2700DB0202R03/12 09/2012 Corner-Grounded Delta (Grounded B Phase) Systems Unassembled and Assembled Equipment 480 Vac UL Listed Grounded B Phase Interrupting Ratings UL Listed 480 Vac Grounded Catalog No. of Footnotes Ampere Rating B Phase RMS Sym.
PAGE 8
Corner-Grounded Delta (Grounded B Phase) Systems References Switchboards 2700DB0202R03/12 09/2012 ENGLISH QED custom switchboards are UL Listed for use on grounded B phase systems when properly rated devices are installed (see the “Devices” section beginning on page 5 for details). QED switchboards can be rated up to 480 Vac as shown in Table 8. Table 8: Switchboard Voltages Type of Switchboard References Schneider Electric USA, Inc.