Changing Existing Stand-By Generator To as Separately Derived System

Hello.

I am very confused and have spent the last 2 hours going in circles.



My scenario.

Some background

NEC 2014 is enforced in my state.

Electric service and stand-by generator are both 277/480V 3 phase Wye connected.



I have an existing 55KW emergency generator installed on an existing 800A service so no GFP is provided on the main service. We are upgrading the service to a 2000A service which will now have GFP. Because of this I need to replace the existing 3 pole transfer switch with a 4 pole transfer switch for proper operation of the new GFP. I am trying to determine the proper way to set this generator up as a separately derived system with respect to the grounding. To make matters more interesting this is an exterior generator on a concrete pad about 30’ from the door to the main electric room. There is currently an 100A -3P circuit breaker installed on the generator which feeds a 3 pole transfer switch inside the building. I have reviewed the NEC specifically 250.30. I was wondering since I need to follow 250.30 and the gen set is installed outside how do we comply? I imagine there will be questions first so Ill answer whatever is needed first. Thanks for responding!
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Also, you are using the term standby and emergency for this system. The terms can't be used interchangeably when discussing NEC requirements. Is it an Article 700, 701 or 702 system? Or some of each?
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
It is a Legally Required Standby (hence my unacceptable use of the word) System . Thanks!
Sorry, didn't mean to chide. As you know, this is an area of the NEC where terms can have a big impact.
Those links I posted are part of a whole series of white papers that Cummins has posted over the years. There are many excellent papers there.
 
Last edited:

tom baker

First Chief Moderator
Staff member
Also, you are using the term standby and emergency for this system. The terms can't be used interchangeably when discussing NEC requirements. Is it an Article 700, 701 or 702 system? Or some of each?
Thank you for clarifying that. My manager where I worked called all generators "emergency". And yes the Cummins papers are very well done.
 
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