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Jason
Jason, Service Technician
Category: Electrical
Satisfied Customers: 4271
Experience:  Over 20 years of experience in all types of installations, troubleshooting, and repairs.
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I have a 100amp service in my house. It is a three wire no

Customer Question

I have a 100amp service in my house. It is a three wire no ground wire installation. I want to run a 100amp service to a shop 150 feet away. I buried three 4/0 copper wires in conduit 3 feet deep from the house to the shop. In the same ditch there are two one inch copper pipes that supply heat to the shop from the house. Can I use one of the copper pipes as a ground connection between the house panel and the shop sub panel? What is the best way to hook this up? I will be using a main breaker panel in the shop.
Submitted: 3 years ago.
Category: Electrical
Expert:  Jason replied 3 years ago.

Jason :

Hello. Welcome to Just Answer.

Jason :

From reading your question, it sounds like you are trying to comply with the Code as much as you can.

Jason :

I'm curious as to why the feed to your main panel isn't grounded. Do you not have a ground wire to the main panel, from a ground rod or a cold water pipe?

JACUSTOMER-m8zr5fk5- :

Not sure. I am 200 miles from the property at the moment.

Jason :

I understand. In order to be Code compliant, you actually need a 4 wire feed from the main panel to the sub. Since the building is not attached to the house, you also need a ground rod at the sub panel. If you don't have room in the conduit for a 4th (ground) wire, you actually could reduce the size of the 3 existing copper wires. They are substantially larger than they need to be for the length of the run, and the load you will be placing on them.

Jason :

Reducing the size would free up room in the conduit for a 4th wire, for grounding purposes.

JACUSTOMER-m8zr5fk5- :

Unfortunately that is not an option. Can I still do the hook up safely?

Jason :

I won't call it unsafe if you have a ground rod at the sub panel. But it just wouldn't be Code compliant.

JACUSTOMER-m8zr5fk5- :

So. This is consistent with what I have seen and read. Let me go through what I understand it to be.

JACUSTOMER-m8zr5fk5- :

I would hook up neutral in the new box to an insulated bar and keep it isolated from the ground bar which would ground hook up to two 8 foot ground rods 6 feet apart. Circuits from this box could be wired as conventional circuits with neutral and ground.

Jason :

Yes, other than we don't typically install 2 ground rods for a 100 amp service. I would only use 2 ground rods on a 200 amp service.

JACUSTOMER-m8zr5fk5- :

Great saves time and money. Will I have any problems from the copper pipe if I leave it unattached to the electrical sytem on both ends?

Jason :

I don't think so. It should be fine. I wouldn't use a heating pipe for a ground.

JACUSTOMER-m8zr5fk5- :

Thanks I think that does it.

Jason :

You are most welcome. Is there anything else I can do for you?

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