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Monday, October 16, 2017

Question:

Re: CQD answer published Tuesday, October 10, 2017 - Generator Grounding 1

In regards to Monday Oct. 9th 2017 Question & Answer: It seems to me the only way Nick’s generator (Separately Derived System) can feed the “Emergency” side of 2- 4 pole ATS’s and 1- 3 pole ATS, is if the 480V to 208/120V  Xfmr. feeding the “normal” side of the 3-pole ATS is three Phase only and has no Grounded conductor. Otherwise he would have to re-ground at the the 3- Pole ATS which as you said would violate 250.30(A).

Thanks, Kelly Wofford

A

Answer:

Hey Kelly it's good to hear from you and thanks for your comment. That would be true if there wasn't a transformer, of if it did not have a delta connected primary which is typical. The grounded neutral conductor of the 480Y277 volt system is not re-grounded because of the 4- pole transfer switches and it is not connected to the 480 primary 208Y120 volt secondary transformer. The 208Y120 volt system is separate so using a three pole transfer switch is acceptable if the grounded conductor is only "grounded" at one point.

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