1、 1 Copyright 2015 IEE. Al rights reserved. Interpretation Section 9. Grounding methods for electric suply and comunications facilities Rule 097B2 Separation of grounding conductors (2012 Edition, page 32) (29 June 2015) IR578 Question: Is the multi-grounded conductor of a corner-grounded delta syste
2、m an aceptable grounding conductor even though it is not specificaly listed in Rule 097B2? Discusion: Corner-grounded delta primary circuits are relatively rare and, as a result, are not directly specified in the NESC as presently writen. However, it is believed that the language of the NESC alowsan
3、d even promotesbonding of the secondary neutral with the corner-grounded delta conductor of the primary circuit, because the multi-grounded primary phase is efectively equivalent to a multi-grounded neutral or overhead shield wire. It is not uncommon for a utility with a corner-grounded delta system
4、 to ground one conductor in acordance with NESC 97C, and for al practical purposes treat this system like a V-phase open-wye system. Electricaly, the grounded conductor in a corner-grounded delta system operates identicaly to a multi-grounded neutral conductor on a wye system meting Rule 230E1. Some
5、 have argued that, because Rule 097B2 does not specificaly mention the multi-grounded phase of a corner-grounded delta circuit, the multi-grounded phase cannot be connected to the secondary neutral. Others argue that the multi-grounded phase of a corner-grounded delta circuit is no diferent from an
6、overhead shield wire as a practical mater and, because Rule 097B2 alows connection of a secondary neutral to a multi-grounded overhead shield wire, connection of the multi-grounded phase of a corner-grounded delta circuit is alowed by the NESC. It is believed that is the case. In terms of safety, if
7、 the primary corner-grounded delta conductor is forced to be separated from the secondary neutral conductor at the transformer supplying the 2 Copyright 2015 IEE. Al rights reserved. secondary service, then the customer is prevented aces to the most efective grounding system available, i.e. the mult
8、i-grounded conductor of the delta system. The customer is then relegated to use a separate grounding system that is usualy les efective and has potential for additional safety concerns due to the separation of grounding systems. The most efective ground for the secondary neutral is achieved by bondi
9、ng to a multi-grounded phase of a corner-grounded delta primary in such cases. Interpretation While the multi-grounded conductor of a corner-grounded delta system is not listed in Rule 097B2, there is no deliberate intent to exclude it. Note that a three-wire delta system may be corner-grounded if e
10、fectively grounded. Se Rule 215B3. Because the NESC does not specificaly cover the system described above, Rule 012C applies. _ National Electrical Safety Code and NESC are both registered trademarks and service marks of The Institute of Electrical and Electronics Enginers, Inc. The NESC is available from The Institute of Electrical and Electronics Engineers, Inc., 45 Hoes Lane, Piscataway, NJ 0854, USA (http:/standards.iee.org/)
