Two services at one campus, but at different buildings, should grounding systems be bonded together?

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palojai

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At a college campus, I designed for two services, (1) 480V, 3 phase, and (1) 208V, 3 phase, where each service is installed at a different building. This campus consists of old buildings that do not have steel and are made of precast concrete. The contractor has submitted an RFI where he is proposing to install a bonding conductor 3/0 from 480V service (switchboard) to 208V service (switchboard) for a hefty fee and is saying the inspector is requiring it.

I have looked at NEC 250, and I cannot find anywhere in the code where it is pointed out that I need to bond two AC services grounding systems together. NEC 250.58 calls out that two AC systems coming in the same building should share a grounding system, but in my case, two services are not in the same building. And buildings that use 208V circuits do not have circuits from 480V service and vice-versa.

Can anyone elaborate or clarify for me, whether I should agree or disagree with the RFI of installing a bonding conductor between two services? I personally do not think a bonding conductor is needed, and that it would be a waste of money and potentially might be dangerous to bond these two services together.
 
If I have two houses on the same lot with different street addresses and separate services, do I need to bond the load centers? No, I do not. Don't let him snow you by challenging you to show in the code where you don't need the bond; that's not how the code works. It tells you when you need to do something, with exceptions. Have him give you the code section he thinks is applicable.
 
Not required. And it can cause objectionable current, as the neutral current from one service may find its way to the other via the 3/0, which would be a violation of 250.6
And as pointed out by Gadfly, they need to submit the code section.
Maybe they have some 3/0 left over from another job...
 
Dumb question: are these buildings entirely separate, or are the electrical systems common across the campus, eg 480V service ends up providing 480V circuits to all campus buildings; similarly 208V is distributed around the campus?

Jon
 
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