bonding

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micary

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Hello,
First entry so I don't know if I'm doing this right.
Having trouble with Art. 250. Please verify my findings.
In short; I believe I'm correct in understanding that in a situation where I have a single phase service disconnect grounded on a utility pole serving a structure, remotely via underground feeders, I need to run a ground conductor with those feeders even though I will be installing a 'driven ground' at the structure also. It seems that Art 250.32 addresses this, but it indicates that the second ground should be bonded to the service ground. I thought that was a no-no.
Please advise.

Thanks,
Mike Krouse
Texas State University-San Marcos Texas
 
Re: bonding

250.32 (B)(1) Equipment Grounding Conductors. An equipment grounding conductor as described in 255.118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrodes. The equipment grounding conductor shall be used for grounding or bonding of equipment,structures,or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122.
( this part should answer your question )
Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrodes.
 
Re: bonding

250.32 is the code section that you need to study. This is a case where the pole is considered a "structure" so you will definitely need a Grounding electrode at the pole. Since the building will be served by more than one circuit you will also need a grounding electrode at the building.
The conductors between the pole and the building are "feeders". Whether you are required to install a ground wire with the feeder is determined by whether or not there are other "continuous metallic baths bonded to the grounding system in each building or structure". These paths could be a telephone or cable TV line, or a metallic waterline for example. If you KNOW there are no other metallic paths you may install three conductors (2 hots and 1 grounded (neutral) conductor) from the pole to the building. Tie the neutral and grounds together just as you would in a new service. Otherwise run four conductors and separate the grounds and grounded (neutral) conductors just as you would in a sub-panel. It is never wrong to install the four conductors and it "future-proofs" your installation against someone in the future installing a metallic path between the two structures. I usually recommend the four conductors, but you need to understand why you are doing it. With only three conductors and another metallic path available you will have neutral currents travelling on "conductors" that are not meant to carry current.
 
Re: bonding

Thanks for the replies. As it turns out, I was mis-reading the article and it is as I have thought all along.

Thanks again,
mike
 
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