MCC GROUND FAULT PROTECTION

[MJK]

I am supplying a 480VAC 3PH, 3Wire, No neutral MCC to an end user for connection to his distribution system. By contract the end user is responsible for the design and specification of his distribution system. The end user has reviewed and accepted my MCC specification, which does not include ground fault protection in this case. The MCC has a 1600A incoming breaker and controls several motors that require an orderly shutdown to avoid increased hazards due to the presence of liquid steel. NEC 230.95 states that GFP is required for each service disconnect rated 1000A or more, however exception 1 clearly states that GFP shall not apply if nonorderly shutdown will introduce additional or increased hazards. Question: Is the exclusion of GFP for the MCC in this case acceptable? If not, who should supply it. Thanks in advance.

 

[pablo02]

Hmmm, fuzzy point in contract, huh... (I was working on ground fault settings today...)

I do not know the process, so I can't say whether or not GFP is required (although sounds legit)... it'll probably be up to the local inspector... if deemed not necessary, I'd try to get something in writing from the owner indicating their request not to have it for stated reasons...

if required, I suspect you may be required to provide at your cost... (look over your PO or contract carefully to see what was actually requested -- you might have a negotiating point for them to pay the price if they specified what they wanted, but didn't mention the GFP) -- I think it would be in your best interests to bring up GFP (it's requirement by code and the exemptions allowed) and have them determine it's requirement (possibly allows you an out to get them to cover the cost)

The GFP will need to be tested, etc. so there are costs associated with this too...

 

[rbulsara]

While I agree with pablo, One way to avoid GFP, is to break the MCC into two 800A units.

Btw, you are referring to a service disconnet, is this a service entrance equipment? However I think newer code requires ( I am not in the office to look up Code book)GFP for any distribution rated 1000A or more on 480/277V grounded system.

 

[jbartos]

Suggestion: It would be prudent to provide the GFP to the 1600A main cb, if not already installed upstream, e.g. visit

http://www.sea.siemens.com/SpecGuide/Sections/Sec21.pdf

for the concept.