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Old 10-25-2012, 09:58 PM   #1
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Steel Building questions?


I'm building a 40 x 30 steel building on my property. It will be used for my personal shop for building hot rods, Etc.
I need to know if it is OK to use 12/2 Aluminum MC Cable through out the building using metal boxes. Or do I have to run all electric in conduit from the sub panel and treat it as a commercial building?

I have a 320/400 amp service on the house already 200 going to the house. I'm going to pull off of the meter with double lugs and I plan on useing a 100 Amp Two-Pole Outdoor Enclosed Circuit Breaker and running 2/0,2/0,2/0,#8 aluminum wire from the house in 2" conduit to a 100-Amp 20-Space 20-Circuit Indoor Main Breaker Load Center. Does this sound good?
I plan on putting a grounding rod at the building to ground the building and the sub panel.

Thanks for looking,

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Old 10-26-2012, 12:01 AM   #2
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Steel Building questions?


You can use MC cable, or you could even use NM cable. Both are required to be protected from damage and neither are wet-rated, so pretty much anywhere that you could legally run MC, you could run NM. In reality MC is quite a bit more durable but the code doesn't acknowledge this. Sleeve the MC or NM in conduit where it is subject to damage.

If you have a main breaker panel, then you don't need the 100A outdoor circuit breaker. Just run directly to the panel from the meter. For grounding, you will need two rods (unless you can prove under 25 ohms impedance, which you can't). You also need to bond the steel building, and if the slab has rebar then you need to bond it too.

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Old 10-26-2012, 02:28 PM   #3
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I think the OP would need the 100 amp breaker as he isn't running 320/400 to the steel building.
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Old 10-26-2012, 04:54 PM   #4
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I think the OP would need the 100 amp breaker as he isn't running 320/400 to the steel building.
The OP mentioned using a main breaker load center, so the outdoor breaker is redundant. As long as the main breaker is properly sized for the wire used, he is good to go.
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Old 10-26-2012, 05:10 PM   #5
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Yes I'm only running 100 amps to the steel building from the house. So I would need one grounding rod for the building and one for the Electric? I need to tie the ground from the building to the grounding rod at the house together correct.
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Old 10-26-2012, 05:16 PM   #6
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Yes I'm only running 100 amps to the steel building from the house. So I would need one grounding rod for the building and one for the Electric? I need to tie the ground from the building to the grounding rod at the house together correct.
You will need two ground rods spaced at least 6ft apart from each other. These will need to be tied together, and tied to the panel. Then, you will need to tie all metal components of your building together to your grounding electrode (Steel frame, metal siding, rebar in the pad).
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Old 10-26-2012, 06:24 PM   #7
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Originally Posted by dawizman View Post
The OP mentioned using a main breaker load center, so the outdoor breaker is redundant. As long as the main breaker is properly sized for the wire used, he is good to go.
So he can run 2/0 straight from a 400 amp meter socket with no fusing? I'm assuming there is some distance beyond the tap rule to the metal building.
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Old 10-26-2012, 07:06 PM   #8
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So he can run 2/0 straight from a 400 amp meter socket with no fusing? I'm assuming there is some distance beyond the tap rule to the metal building.
As far as I know, the code states that the first disconnect must be "as close as possible" to the meter. In my opinion, you could run over to the shop without a breaker mounted near the panel. In the end, the inspector will have the final say, so ask your ahj what they want to see done
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Old 10-26-2012, 07:46 PM   #9
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If these will be service conductors coming directly from the meter, with no disconnect between the meter and the building panel only three conductors will be needed to the building and the panel should be connected as a service panel.
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Old 10-26-2012, 08:07 PM   #10
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There is a distance of 115' between the house and the garage ( meter can to service). To be clear I can just run my 2/0 strait off the meter can under ground to the service panel in the garage? I thought that I would need to have a breaker next to the meter then go to the garage? That and I don't need to run the ground from the garage to the house, keep them separate? I don't live in the city limits.

Thanks,
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Old 10-26-2012, 08:09 PM   #11
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There is a distance of 115' between the house and the garage ( meter can to service). To be clear I can just run my 2/0 strait off the meter can under ground to the service panel in the garage? I thought that I would need to have a breaker next to the meter then go to the garage? That and I don't need to run the ground from the garage to the house, keep them separate?

Thanks,
This should be okay, but to be sure you should talk to the ahj (whoever will be doing the electrical inspection)
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Old 10-26-2012, 08:11 PM   #12
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I need to know if it is OK to use 12/2 Aluminum
Is there a reason you wouldn't use copper? Do you already have a bunch of the aluminum?
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Old 10-26-2012, 08:12 PM   #13
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Quote:
Originally Posted by dawizman View Post
As far as I know, the code states that the first disconnect must be "as close as possible" to the meter. In my opinion, you could run over to the shop without a breaker mounted near the panel. In the end, the inspector will have the final say, so ask your ahj what they want to see done
I'm not positive, but I'm pretty sure it's "as close as possible" to the point where the service conductors enter the building, not to the meter. In other words, the service entrance conductors can be as long as you want outside of a structure. Maybe someone will have a code citation that states otherwise.
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Old 10-26-2012, 08:32 PM   #14
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edit out

Last edited by zappa; 10-26-2012 at 08:41 PM.
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Old 10-26-2012, 08:35 PM   #15
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Steel Building questions?


The reason I'm running Alum. is the cost. is about half.

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