Separately Derived System Grounding Electrode

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Clayton502

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I recently inspected a building that had a new generator installed. The transfer switch switches the grounded conductor (neutral). The neutral and equipment grounding conductors are bonded at the generator and ground rods installed at the generator. Since this is a commercial building with a steel building frame I sited 250.30(4)1. Seems to me that with no solid neutral connection that the building steel or water pipe as in 250.30(4)2 must be used as the grounding electrode not the ground rods at the generator. The engineer for the job disagrees. Any opinions on this? Thank You
 
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benaround

Senior Member
Location
Arizona
Re: Separately Derived System Grounding Electrode

Clayton,

Do both systems have EGC at the ATS, If they do then the GES would be tied into the gen set. More importantly would be an effective EGC back to the gen set grounded conductor,or bus.
 
George Stolz

George Stolz

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Windsor, CO NEC: 2017
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Re: Separately Derived System Grounding Electrode

I don't quite understand your response, Frank. It is an SDS, it would need to be grounded to the steel structure per Clayton's reference, wouldn't it?

I'd imagine the bonding paths are present, right Clayton? Grounding seems to be the question, right?
 
dereckbc

dereckbc

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Location
Plano, TX
Re: Separately Derived System Grounding Electrode

Clayton, If I understand you correctly, then I agree because the building shall be served by a common electrode to comply with 250.58.

IMO all the client has to do is bond the genset rods to either building steel or other electrode that forms the GES.
 
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Clayton502

Member
Re: Separately Derived System Grounding Electrode

Yes, both systems (generator and normal power) have equipment grounding conductors ran to a common grounding bar in the ATS. I realize that building steel is connected thru the equipment grounding conductors of both systems but I didn't think that this could be used in place of a grounding electrode conductor as per 250.30(4)1 or 2. The way I am interpreting that code section is that the steel structure or water pipe is to be used for the required grounding electrode and that ground rods at the generator could only be used as the sole grounding electrode if the steel and metallic water pipe where not present. What I had asked to be done was for a separate grounding electrode of proper size be run from the generator to the building steel. I hope I wasn't to off base with my interpretation.Thank you
 
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benaround

Senior Member
Location
Arizona
Re: Separately Derived System Grounding Electrode

Clayton,

I agree,you made the right call. Sorry if I confused the issue with my first post.

frank
 
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