Independent grounding of switchboards in the same room.

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Dustin Foelber

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I have a project in which we have an existing switchboard containing a 1600A Main. This main feeds our new Main Lug switchgear that has multiple breakers feeding new panelboards. The drawings call for this new switchboard to be grounded with steel, cold water, and the ground in the sub-feed. It is my understanding that a sub-panel in the same room (or building) should not be grounded again if the equipment feeding it is already grounded as a main board/service entrance. Unfortunately I do not have a complete understanding of this from an electrical stand point. Any feedback is appreciated.

Thank you.
 
Depends on what you mean by grounded. If you mean there is a conductor that goes from the grounding electrode system to the neutral of the new switchboard the answer is that is probably prohibited.

However, nothing code wise that I can think of offhand prevents you from connecting the GES to the equipment ground bus of the new switchboard.
 
That is what I am curious of why would you ground both pieces of equipment and bond the neutral at both? Especially when you have an overcurrent device at the existing MSB on the secondary of the transformer. See cut below.
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Yeah I don't see anything prohibiting connecting the GES to the EGC bus of a sub, as long as it also connected to the proper place. A single point earthing system is probably better however

Just to clarify, my previous post didn't come out right. The GEC can connect anywhere from the service point up to and including the service disconnect.
 
Dustin Foelber said:
That is what I am curious of why would you ground both pieces of equipment and bond the neutral at both? Especially when you have an overcurrent device at the existing MSB on the secondary of the transformer. See cut below.
View attachment 2557252
Click to expand...
You can connect the GES to the EGC bus of a sub, but I can't think of any reason to do so. What you cant do is connect the GES to the neutral downstream of the service disconnect or bond N-G past the service disconnect.
 
The drawing you provided shows the neutral bonded to the EGC bus so obviously there is an error. This cannot be bonded downstream of the 1600 amp disconnect. This could be a boilerplate drawing that no one even looked at.
 
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