Neutral in Automatic Transfer Switch
Neutral in Automatic Transfer Switch
(OP)
I saw automatic transfer switch with 4 pole where neutral of both source connected to one pole of switch and neutral of both switch never mixed.
I saw automatic transfer switch with 3 pole where 3 phases are connected to 3 poles and neutral is connected to common neutral bus. In this case neutral of two different source is connected together in common neutral bus.
I think neutral of two source should not mix together.
Dose CSA or ANSI code says about automatic transfer switch ?
I appreciate comment on this issue.
Thanks to all
I saw automatic transfer switch with 3 pole where 3 phases are connected to 3 poles and neutral is connected to common neutral bus. In this case neutral of two different source is connected together in common neutral bus.
I think neutral of two source should not mix together.
Dose CSA or ANSI code says about automatic transfer switch ?
I appreciate comment on this issue.
Thanks to all






RE: Neutral in Automatic Transfer Switch
We would need to see a system 1-line drawing to provide a more definitive answer.
IEEE Std 446 "Orange Book" has a lot of information on this subject.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Neutral in Automatic Transfer Switch
Non-separately systems, where the neutral is interconnected and grounded only at one point (at one of the sources). These system would permit 3 pole transfer switch with solid neutral. For more look up NEC code book. The idea is not to ground the neutral of the source at more than one point on customer premises.
4-pole transfer switches are also useful on premises with more than two sources, such as one generator but multiple utility services/substations.
Rafiq Bulsara
http://www.srengineersct.com
RE: Neutral in Automatic Transfer Switch
However, there may be other considerations such as ground current detection schemes, long distances to an alternate source such as a standby generator or other issues that are best addressed by using a four pole transfer switch.
An example may be a standby generator that is a long way from the transfer switch and it is desired to ground the neutral at the generator rather than with a common ground at the main panel. This issue may be addressed by switching the neutral in a four pole transfer switch.
Bill
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"Why not the best?"
Jimmy Carter