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Old 09-11-2011, 09:18 AM   #1
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Expanding load center capacity in barn


I have a barn that appears to have 70A/240V service (based upon the ratings of the breaker in the main house). There is currently a QO six space main lug load center, but I am hoping to be able to add more circuits (a couple of 2-pole, plus multiple single poles). I've already "doubled up" as much as I can. So, I need more space.

I have a few questions about this...

1) I'm not finding any good choices for 70A load centers. Can I use 100A?
2) Should I use "main lug"? It would be great if the load center had a main breaker of its own (to make it easy to power off everything locally if need be), but I'm not finding any 70A main breakers that can be user-installed.
3) Am I better off just adding a small subpanel next to the existing panel?

Thanks,
Eric

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Old 09-11-2011, 09:38 AM   #2
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Expanding load center capacity in barn


If you have a 70 amp breaker in the house feeding the barn, you can put a 100 amp panel with a main breaker in the barn. The 100 amp breaker is just a disconnect.

Is this a 4 wire feed?

Do you have ground rods at the barn?

What is the load at the barn?

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Old 09-11-2011, 09:43 AM   #3
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Expanding load center capacity in barn


A 100 amp main breaker panel typically has space for 20 poles of breakers and is around $100.
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Old 09-11-2011, 10:10 AM   #4
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Expanding load center capacity in barn


The big box stores have 100 amp load centers "contractor packages" for $50-60. They include the 100 amp main breaker and 5 20 amp single pole breakers. Various different brands; GE, Cutler Hammer, Square D
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Old 09-11-2011, 08:01 PM   #5
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Expanding load center capacity in barn


Thanks for all the help.

To answer the questions above, the feed is 3-wire. There is one ground rod just outside of the barn wall behind the panel. Not sure of the load.

Is that okay?

Thanks again

Eric
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Old 09-11-2011, 08:45 PM   #6
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Expanding load center capacity in barn


Quote:
Originally Posted by mn1247 View Post
Thanks for all the help.

To answer the questions above, the feed is 3-wire. There is one ground rod just outside of the barn wall behind the panel. Not sure of the load.

Is that okay?

Thanks again

Eric
Depending upon which Code cycle was in effect at the time of the original installation it might be compliant.
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Old 09-11-2011, 09:58 PM   #7
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Expanding load center capacity in barn


Since this is existing you would be fine, unless there was another metallic path like a phone or water line back to the house.

With only a 3 wire feeder you will again bond the neutral and grounds.
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Old 09-13-2011, 09:00 AM   #8
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Expanding load center capacity in barn


Perhaps I should add that the 3-conductors are encased in metal conduit, and that is grounded. So, maybe that's the 4th conductor???

Yes, there are water an phone lines back to the house, though the water line is CPVC. Am I okay? The phone line runs alongside (but not inside) the metal conduit.

Thanks again,
Eric
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Old 09-13-2011, 09:24 AM   #9
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Expanding load center capacity in barn


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Originally Posted by mn1247 View Post
Perhaps I should add that the 3-conductors are encased in metal conduit, and that is grounded. So, maybe that's the 4th conductor???

Yes, there are water an phone lines back to the house, though the water line is CPVC. Am I okay? The phone line runs alongside (but not inside) the metal conduit.

Thanks again,
Eric
The metal conduit probably will qualify as a grounding conductor.

Separate the grounds and neutrals.

You probably need 2 rods. 1 rarely meets the 25 ohm or less requirement.

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