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#23732 - 03/25/03 07:01 PM back up generator
wolfdog Offline
Registered: 10/24/01
Posts: 135
Loc: Dallas,TX
This question was asked of me at another web site and I don't have a good answer. Would you folks enlighten me so I can pass it on.

Consider a commercial building with a three phase service and 100% generator back up.

If you use a 3 pole transfer switch, you don't break the neutral.

If you use a 4 pole switch, you break the neutral, add some extra grounding, and the system is now "Separately Derived".

When in your opinion do you have to have the 4 pole transfer switch and the separately derived system?

I would like your opinion on tapping service feeders also.

[This message has been edited by wolfdog (edited 03-25-2003).]
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#23733 - 03/25/03 08:05 PM Re: back up generator
russ m Offline
Registered: 02/22/03
Posts: 169
Loc: Burbank,IL,USA
Try these links.;f=18;t=005123;f=18;t=005233#000000
#23734 - 03/25/03 09:26 PM Re: back up generator
Nick Offline
Registered: 08/13/01
Posts: 599
Loc: Riverside, CA
Short answer: When ground fault protection is required on either the service entrance or generator or both.
#23735 - 03/26/03 04:44 AM Re: back up generator
wolfdog Offline
Registered: 10/24/01
Posts: 135
Loc: Dallas,TX
Thanks for the responses and links.

Obviously, I have not been keeping up very well with the Mike Holt forum.

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