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#23732 - 03/25/03 11:01 PM back up generator  
wolfdog  Offline
Joined: Oct 2001
Posts: 135
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 - 03/26/03 12:05 AM Re: back up generator  
russ m  Offline
Joined: Feb 2003
Posts: 169
Try these links.;f=18;t=005123;f=18;t=005233#000000

#23734 - 03/26/03 01:26 AM Re: back up generator  
Nick  Offline
Joined: Aug 2001
Posts: 599
Riverside, CA
Short answer: When ground fault protection is required on either the service entrance or generator or both.

#23735 - 03/26/03 08:44 AM Re: back up generator  
wolfdog  Offline
Joined: Oct 2001
Posts: 135
Thanks for the responses and links.

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

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