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1.5, 3, and 5kva transformer grounding. #81641 09/04/02 06:59 AM
Joined: May 2002
Posts: 202
jlhmaint Offline OP
which section in the code will cover this and explain. please there are some different views at work and would like to clear this up. some are just hooking a ground to the metal case, others are tying X1 to ground and grounding the case. I have seen it done both ways or not at all. note these are typical 480V to 120 V

[This message has been edited by jlhmaint (edited 09-04-2002).]

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Re: 1.5, 3, and 5kva transformer grounding. #81642 09/04/02 01:03 PM
Joined: Jul 2002
Posts: 175
electric-ed Offline
I can't quote code rules, as I do not know the NEC well enough, but the basic principles of grounding and bonding are similar everywhere.

The sketch below shows grounding and bonding for a typical single phase stepdown transformer.

[Linked Image from]


Re: 1.5, 3, and 5kva transformer grounding. #81643 09/04/02 02:57 PM
Joined: Nov 2000
Posts: 2,148
resqcapt19 Offline
These are Separately Derived Alternating-Current Systems as covered in 250.30. Eds drawing is right on the mark.

Re: 1.5, 3, and 5kva transformer grounding. #81644 09/04/02 10:05 PM
Joined: May 2002
Posts: 202
jlhmaint Offline OP
ok that pic shows exactly how we do it in our building but we have seen some from our other building that were not like that or no ground or bond at all. Thanks

Re: 1.5, 3, and 5kva transformer grounding. #81645 09/04/02 10:48 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
I may be missing something, but don't {99NEC} 250-30 and 250-26 fairly well cover the matter? The sizes listed are all above 1000VA. Probably one aspect of the ‘building steel’ versus “case” ground, it would seem more critical if the wiring runs extended out of a local area. [In the case of an open secondary bonding jumper, it’s maddening to have to do much troubleshooting on ungrounded 120V controls.]


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