Main Lug or Main Breaker to feed shop?

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  #1  
Old 07-10-12, 08:14 PM
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Main Lug or Main Breaker to feed shop?

Hello, I'm new here and seeking some advice. First off, I'm in Louisiana. My area uses the NEC 2008 as the electrical code.

I'm planning to run power to my detached shop soon (hopefully). When we built the house, I spoke to the power co. and asked the best way to prepare for bringing power to my shop. I wanted 200A for the house and 100 or more to the shop. They sold me a Milbank 320A meter socket which has double-barrel lugs. One barrel of the lugs feeds the house. The other will feed the shop. I intend to install a 125A panel at the house. That will feed another 125A panel in the shop. I'm sure I can just feed straight to the shop, but I figure it would be convenient to be able to cut power to the line feeding the shop if ever needed. The panel in the shop will have a main breaker. What I'm unsure about is should that first panel at the house have a main breaker plus a 125A branch circuit breaker to feed the shop panel, or should it just be a main lug with a 125A branch circuit breaker feeding the shop panel. Keep in mind the panel at the house will only be feeding the shop, so there will be no other breakers/circuits in it. As per NEC and best practices, which is the correct way? I've included a picture to hopefully help my explanation.

Thanks in advance for any help.
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Old 07-10-12, 10:55 PM
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The second panel in your house needs a main breaker AND the branch circuit (to the shop) breaker IF it has the ability to have more than just the single 2-pole branch circuit breaker. If you get a panel that has only the one 2-pole breaker AND it is located closer than ten feet from the meter then you do not need two (main and branch) circuit breakers.
 
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Old 07-11-12, 07:06 AM
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This type of setup is a bit past my experience level, but might it make sense to just use a fused disconnect in the house instead of a panel? I don't know about cost, but I think it would be much cleaner than a practically empty 125A panel.

If you do use a main panel in the house, you need to be sure whatever panel you get has 100A breakers available. Maybe they all do now, but I think in the past, some home panels didn't accept breakers that large.
 
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Old 07-11-12, 08:23 AM
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You could set a disconnect for the garage next to the 200 amp panel to satisfy keeping the services grouped.

You will need a means of disconnect at the garage. The feeder would also need to be 4 wires.
 
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Old 07-11-12, 05:56 PM
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it make sense to just use a fused disconnect in the house instead of a panel? I don't know about cost, but I think it would be much cleaner than a practically empty 125A panel.
Agreed, but....that would require a 200 amp fusible switch fused at 125 amps. It would be less expensive to install an enclosure with a 2 pole 125 amp breaker.
 
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Old 07-11-12, 08:19 PM
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Thanks for the information. Let me provide a few more details that I left out. The length of run to the shop is about 130 ft. I already have the wire run. It is oversized for what I need, but the price was right. It is 4/0-4/0-2/0 AL and I ran a #4 CU ground along with it. I intend to reduce the wire size as needed at the panels. The 200A panel for the house is outdoor, next to the meter.

Let's change it up a bit. I think I may downsize the shop service to 100A. Does the disconnect at the house for the shop have to be fusible or some other form of circuit protection if I have a main breaker in the shop panel? Reason being, I have a 100A non-fusible disconnect (safety switch). Can that be used as my "means of disconnect" and then feed from that to the shop panel? The disconnect is a Siemens NFR323. See the attached picture. It is 3 phase, but I believe it can be used as single phase, correct? I'm sure 100A would be plenty for my needs. My shop is only 24x24 and I have a few woodworking tools, air compressor, and welder. Would this be a feasible or even better way to do it?
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Old 07-11-12, 08:33 PM
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Does the disconnect at the house for the shop have to be fusible or some other form of circuit protection if I have a main breaker in the shop panel?
Yes. Otherwise the feeder cable is not protected. A non-fusible disconnect is, as you noted, a safety switch.

You just upped the ante when you said that
The 200A panel for the house is outdoor, next to the meter.
That means that your disconnect needs to be in a NEMA 3R enclosure. I suspect, looking at the picture that you posted of the label on the 3-phase safety switch, that you're already aware of that.
 
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