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GEC sizing for detached building

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Josuea1990

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If you are requiered to establish a grounding electrode system on a detach building because you are bringing feeders to power a remote distribiuton panel for this detach building, and one of your existing electrodes in this building like a water pipe uses 250.66 wich uses the size of service entrance conductors table to size the GEC. ¿Do you still have to size your GEC based on the service entrance consuctors?. Altought the feeders that you are bringing to feed this building are not service conductors? , i mean, they are feeders and they have their own OCPD. How do you do the seizing on this scenario for GEC?
 
Dennis Alwon

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hbiss said:
All you need to do is drive two ground rods and run #6 for the GEC to the subpanel ground bar.

-Hal
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I think the op is asking if he has a feeder that is 60 amps then what size grounding electrode conductor would you use to connect the water pipes that enter the building?
 
infinity

infinity

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It's a good question. Does the NEC actually say how to size the GEC(s) when there are no service conductors? Does T250.66 Note 2 apply?
 
infinity

infinity

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electrofelon said:
Well there is note #2 to T250.66..... but I guess it's still not clear if this would be a "no service entrance conductor" situation.
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And that table is used for conductors without overcurrent protection which doesn't exactly fit for the GEC at the end of a feeder.
 
Dennis Alwon

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infinity said:
And that table is used for conductors without overcurrent protection which doesn't exactly fit for the GEC at the end of a feeder.
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Table 250.66

250.66 Size of Alternating-Current Grounding Electrode Conductor.
The size of the grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system of a grounded or ungrounded ac system shall not be less than given in Table 250.66, except as permitted in 250.66(A) through (C).
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Dennis Alwon

Dennis Alwon

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infinity said:
If I have a 125 amp feeder to a separate building what size GEC do I need? I would guess that it's based on the feeder conductor size but I don't see that as being clearly defined.
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We know that we need a grounding electrode conductor at the structure and we know that the grounding electrode conductor for services is based on conductor size.
Section 250.66 tells us to use T250.66 for the grounding electrode conductor. The entire table is based on conductor size. Not sure what else you would be looking for. The feeder amperage isn't important since the Table is based on the conductor size for that feeder.

Services also-- we always say a 200 amp service requires a #4 grounding electrode conductor but it could be larger if your service conductors were increased for some reason.
 
infinity

infinity

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Dennis Alwon said:
We know that we need a grounding electrode conductor at the structure and we know that the grounding electrode conductor for services is based on conductor size.
Section 250.66 tells us to use T250.66 for the grounding electrode conductor. The entire table is based on conductor size. Not sure what else you would be looking for.
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I'm not disagreeing with you I'm just asking where the specific wording is in the NEC that says when sizing the GEC for a separate structure fed by a feeder to use the feeder conductor size to size the GEC.
 
electrofelon

electrofelon

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LarryFine said:
Doesn't saying to use the same table for feeders cover that?
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To me that says yes use the table for feeders, but it does not say to get the size from the feeder. The table column heading says to get the size from the service entrance conductors. As mentioned, maybe we can use note number two to get us there, but I always thought that was for where the service had no service entrance conductors.
 
augie47

augie47

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250.32(E)
(E) Grounding Electrode Conductor. The size of the grounding electrode conductor to the grounding electrode(s) shall not be smaller than given in 250.66, based on the largest ungrounded supply conductor. The installation shall comply with Part III of this article.
 
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