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Old 11-06-2008, 03:34 PM   #1
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New House and Shop Building Service


I am building my own house and part of the work that I have taken on is the electrical wiring. I am getting ready to install the meter can and the main breaker panels. I am looking at having a 400 amp service for the house and a detached workshop. I was originally looking at installing two 150 AMP main breaker panels in the house and one 100 amp panel in the workshop. I was going to come off of 400 amp meter can with direct connections to each of the 3 panels with 3 cables (2 hot, 1 neutral) using 2/0 for the 150 amp house panels and 1/0 for the workshop which is 130 feet away from the meter can. I have had trouble finding 3 position lugs for the 400 amp meter can so am looking at changing the way things are run. Now I am going to feed two 200 AMP main breaker panels from the meter can with 2/0 and then run the 1/0 from a 100 amp breaker in one of the 200 amp panels out to the detached workshop. My question is will this second scenario work and what do I need to do for the ground on both ends?

Rbeard

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Old 11-06-2008, 05:01 PM   #2
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Ideally, you will place the disconnects outside at the meter, or have a meter socket with dual 200 A breakers. From this you need to feed the panels with 4-wire cables, and bond the ground and neutral at the outside main, but keep them separate in the panels. Feed the shop with a 4-wire feeder, and drive a couple of ground rods at the shop and tie them to the ground in the subpanel.

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Old 11-07-2008, 10:51 AM   #3
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The two panels I have for the inside of the house have 200 amp breakers already installed. Should that be ok? Also if there is no other connection between the house and the detached workshop can I get away without runing a ground all the way back to the meter (expensive wire) and just ground outside the shop with ground rods.
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Old 11-07-2008, 12:14 PM   #4
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The two panels I have for the inside of the house have 200 amp breakers already installed. Should that be ok? Also if there is no other connection between the house and the detached workshop can I get away without runing a ground all the way back to the meter (expensive wire) and just ground outside the shop with ground rods.
It's okay, but you do not need a main breaker in the house sub panel, only the main service panel.
You will need a disconnect outside at the garage/workshop, the main breaker in one of these panels will suffice. You could use one of these in the garage/workshop. Then get a lug panel for the house sub panel.

You do not have to run a 200 amp service to the workshop, but you still can use one of the 200 amp panels you have. You will feed the 200 with the breaker of your choice (60 amp min) from either the main service panel or the sub panel inside.
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Old 11-07-2008, 01:20 PM   #5
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Originally Posted by Rbeard View Post
The two panels I have for the inside of the house have 200 amp breakers already installed. Should that be ok? Also if there is no other connection between the house and the detached workshop can I get away without runing a ground all the way back to the meter (expensive wire) and just ground outside the shop with ground rods.
How far does the cable run from the meter can to the panels? I ask because you really don't want, and your inspector may not allow, more than a few feet of un-fused conductors inside the building. Here's the rub: The ground and neutral bond needs to occur at the first means of disconnect. If you have two panels, each being a main disconnect, then each neutral must bond there. Now, you also have to connect each one to a common grounding electrode, and this would allow a parallel path for neutral current, a no-no.

You can keep the panels with the mains, but I would put a disconnect of some sort outside for each one, and use a 4-wire cable to feed them. This allows you to have a single point for the grounding electrode, and provides a means to disconnect the feeders going inside.

As for the shop wiring, you really should have 4-wires. It really depends on what code your area is under. Up to and including the 2005 Code, you were allowed to run a 3-wire feeder to a remote subpanel and bond the grounds and neutrals again, as long as there were no other metallic paths back to the house. In the 2008 code, this was outlawed. As it should be. I ave never liked the 3-wire practice myself, because it allows neutral current to flow through the earth. Really, if you are already spending the money to do all of this, then one more #6 isn't going to break the bank, especially where safety is concerned.
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Old 11-07-2008, 01:53 PM   #6
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The two 200 amp Main breaker panels are on the other side of the block wall from the 400 amp meter base. Everything will be back to back and run through conduct between the mater can and the two panels. I was not planning on putting any other means of disconnect for these two panels. Unless required by code.

I think I permitted under the 2005 code but not sure. For the detached workshop there are no other connections between them at this point but at some point I will be running data/voice/video and water (PVC pipe) to the shop. The panel for the workshop will have a 100 amp main breaker which will be connected back to the 100 amp breaker in one of the 200 amp panels.

I guess a 150 ft of cable for the ground won't break the already broken budget. What type of cable would you suggest for the ground to the workshop? Can it be #6 THHN through the 2" conduct that is being run for the two hot and neutral conductors? Or do I need something different. I don't want to get myself electrocuted when I turn on a saw that is malfunctioning.

I hope I'm not making this more complicated then it has to be.
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Old 11-07-2008, 02:36 PM   #7
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You should probably place the grounding electrode on the neutral in the meter socket, after consulting with your inspector and power company. This would be the best place for it, but some power companies and inspectors won't allow it because after the socket is sealed, it isn't accessible. You can wire the two panels to one electrode, but like I said earlier, this would allow a parallel path for neutral current. But, as far as Code goes, it is legal to do what you want, since the install is back-to-back. And a #6 THHN would be fine for the ground at the remote building. You do really need this ground, since if you install phone and cable, you will be able to bond them to it, instead of the neutral at the sub.
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Old 11-07-2008, 02:49 PM   #8
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Thanks for the help, I think I am going to contact the inspector before I go to far to make sure I meet any local requirements. I spoke with him before and he said to give him a call with any questions I might have since I'm doing my own electrical work.
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Old 11-07-2008, 03:08 PM   #9
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Thanks for the help, I think I am going to contact the inspector before I go to far to make sure I meet any local requirements. I spoke with him before and he said to give him a call with any questions I might have since I'm doing my own electrical work.
Excellent idea. He can make your job easy or hard. Getting him involved is a good way to start.
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Old 11-07-2008, 04:19 PM   #10
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Just got off the phone with the inspector and he said I could run #6 ground from the meter can to two 8' ground rods and then to the rebar that is sticking out of the slab then run a #4 THHN ground wire to the workshop and add another ground rod at the workshop location.

He did not say anything about running the ground from the meter can into the two 200amp main breaker panels. Do I need to continue the ground into the house since the meter can and the main breaker panels will be connected by plastic conduct?

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