Seperate structure grounding

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Dustin Foelber

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I have a project where we replaced the existing utility transformer with a new 3000 amp switchgear. The old transformer was feeding a 1200 Amp gear. We intercepted the conduits coming from that gear and reworked them into our new 3000 amp gear. I then repulled a triple feed of 600 MCMs to refeed the old 1200 amp gear. I am feeding it with a 1200 Amp subfeed breaker at the new gear and the 1200 amp gear also has a main breaker.

Here is my question/mistake.

When I pulled the triple 600 MCM I sized my ground to the individual run and not to the 1200 amp overcurrent. Basically I ran a 2 AWG instead of the required 1/0 per the paralell full size ground requirements. I am wondering because it is a seperate structure and is grounded seperately (no nuetral bond but has its own UFER and CW grounds) is there any exception anyone is aware of where the number 2 ground can be considered adequate? I really appreciate your help guys.
Dustin-
 
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iwire

iwire

Moderator
Staff member
Location
Massachusetts
Dustin Foelber said:
I am wondering because it is a separate structure and is grounded separately (no neutral bond but has its own UFER and CW grounds) is there any exception anyone is aware of where the number 2 ground can be considered adequate?
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Unfortunately no, there are no exceptions, the uffer has nothing to do with the EGC.

Any chance this installation is under the 2005 NEC or earlier?
 
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cpal

Senior Member
Location
MA
If your under the 02, and there is not any inter connecting metal between the structures (I think) you might not need a egc with the feeders to structure #2.

What type of raceway tothe second structure??
 
iwire

iwire

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Staff member
Location
Massachusetts
Yes, as cpal was mentioning under the 2002 NEC you might be able to use the neutral as the grounding means and abandon the EGC.

Read 225.32(B)(2) carefully and see if you meet all the qualifications.
 
K

KevinVost

Senior Member
Location
Las Vegas
iwire said:
Yes, as cpal was mentioning under the 2002 NEC you might be able to use the neutral as the grounding means and abandon the EGC.

Read 225.32(B)(2) carefully and see if you meet all the qualifications.
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I think Bob meant to say 250.32 B2 (there is no B2 section in the 02 code for article 225):grin::grin:
 
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Dustin Foelber

Senior Member
My new 3000 amp gear is free standing (replaced existing utility padmount transformer). Conduit is PVC sch 40. I looked into the code referenced and it appears I can only have the nuetral serve as my EGC if the feeders are not supplied by a subfeed breaker. Is that how you interpret it? Thanks again for your input. I am really in a bind on this one.
 
M. D.

M. D.

Senior Member
Not quite ,.. if the gear is a seperate structure which it sounds like it could be ,and there is no other metallic connection between the two structures then the requirement for the EGC is optional and the equipment in the second building can be bonded to the neutral regardless of the fact there is an OCPD.

http://ecmweb.com/nec/code_top50nec_102506/
 
M. D.

M. D.

Senior Member
From the link,...

This is only permitted where there?s no continuous metallic path between buildings and structures, and ground-fault protection of equipment isn?t installed on the supply side of the feeder.
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