ECN Forum Forums General Topics of the Trade General Discussion Area Underground supply

You are using #2 gauge wire so I am assuming you are going to use a double pole, 100-amp breaker to feed the sub panel on your house.

You will need to run three #2 gauge wires,(two hots and one neutral), from your main panel at the garage to the sub panel on your house. Along with one #8 gauge copper wire for your equipment ground, (Earth).

This is all of the grounding or Earthing that you will need to do. You don't need to drive ground rods in the earth. The #8 gauge equipment ground comming from the garage is sufficient for your ground faults. You still need to run a separate bare copper ground wire from the sub panel to your gas line and metal water line.

Like Tom posted, you will need to keep your equipment ground and neutral wire separate inside of the sub panel on your house. To do this you will need a ground buss bar bolted directly to the sheet metal of the can. (for all of your grounds,(earths), to land on. (Usually the bare copper wires). Then another buss bar called the neutral buss bar mounted inside of the sub panel on your house. Mount it in such a way that it is insulated from the metal can. They come with a plastic spacer to keep it off of the metal can. This is were the #2 neutral wire will land, comming from the main panel at the garage. Also this is were all of the white wires that go into your house will land.

The sub panel will need a 100-amp main breaker. Make sure you don't get a Main-Lug-Only type sub panel. (MLO).

Tev

guys....it's actually easier to find #2 URD quadriplex, probably pull easier in 2" too

Straightedge: How do plan on complying with article 250.32?

You will need to drive at least one rod.

Ryan,

I am not able to look up your code reference, for I only have the 1996 code book. I do want to reply.

I don't understand why you have to put a ground rod at a sub panel. I install sub panels all of the time on houses. Usually only three feet from the main panel. I never install a ground rod with my sub panels.

I am of the understanding that the separate equipment grounding conductor, (EGC). Is all that is required.

Learn me.

Tev

Straightedge: The grounding electrode is required because it is a separate structure supplied from a common AC service. Look at 250-24 of your 1996 NEC.

Ryan,

Thanks, I do have the 1996 code book. 250-24 (a) exception no. 2: Exempts aznewsh from having to pound a ground rod.

As long as he runs an equipment grounding conductor with the circuit conductors for grounding any noncurrent-carrying metal equipment.

The reason I am against another ground rod is because it introduces a second direct path to earth. I believe there should only be one path to Earth. At the main service panel.

Tev

Tev: I apologize, I should not have posted the reference to the 96' NEC. The current code is much more restrictive.

My (and local inspectors) interpretation of this part of the code is this:

Feeding a separate structure from the main service can be done both ways.
One is the way described. Sepearate ground and neutral conductors and keep the grounds and neutrals separate in the subpanel.
The other is to run only the grounded conductor and no ecg. In a sense the new structure becomes another main panel. Ground and neutrals can be together. We run 3 wire URD for this purpose.
I don't have my books at home with me but I know it is in there in not too complicated terms. This exact scenario was debated in a code meeting with all the brass out of Albany, NY not too long ago.

Bottom line is if you run 3 wire it's treated as another main panel. If you run 4 wire it's a sub-panel even though it's in a separate structure.

Either way you need a ground rod (or two) at the separate structure.


For a purpose such as yours we often use a feed-through panel. This has a main breaker at the top with usually 6 or 8 spaces and main lugs a the bottom. This means the full load can be drawn off the main without the need for a sub-breaker.