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Upgrading service in detached garage

Dusty Floor

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Feb 20, 2011
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I have a detached garage used mostly for storage that is fed via an overhead cable from the service panel in the house. It's currently set up with a two breaker box, where one breaker controls the overhead door outlet, and the other controls 3 outlets and lights.

The disconnect in the house is a dual pole 20A breaker; the breakers in the garage are 10A (although I believe the outlets are wired with 12 gauge wire).

I planning to run a feed from this building to a post light and gate controller along the driveway, and would like to add outlets in more convenient locations for running power tools (circular saw, chop saw, etc.) in the driveway and Christmas lights. Ideally, these would be on separate circuits. I don't forsee a need to use heavy equipment, so don't really need additional capacity (although I should have at least one 20A circuit); I'm really just looking to add some flexibility.

We're also planning to repave the driveway next Spring, which would give me an opportunity to bury and possibly upgrade the service feed (it's probably 60-70'). I'm thinking of replacing the box now (with a 20A main breaker), and upgrading to perhaps 30A when a new feed is run.

The first gotcha I can think of is that I may have to relocate the panel, as the existing box is small and in the cavity between the overhead and service doors; I'm not sure a bigger panel will fit there. Given the two circuits, it shouldn't be a problem to extend them to the other side of the service door (which also happens to be closer to the existing ground). Is there anything else I should be thinking about?
 
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pattenp

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Even if you feel you don't need a large service to the garage I highly recommend you do at least 50A - 60A 120/240V service to the garage. The cost of materials is not that much more and I truly believe in the future you'll be glad you put a larger service than 20A or 30A. It will be an added plus at resale.
 
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toplessHO

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Its cheaper to run 120/240 vs 2-120 circuits agree with above.
Just curious about the comment on having 10A breakers.
Are you sure they arent 15A?
As for the relocation just use a J box and extend the circuits to the new panelboard location.
 

pattenp

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Its cheaper to run 120/240 vs 2-120 circuits agree with above.
Just curious about the comment on having 10A breakers.
Are you sure they arent 15A?
As for the relocation just use a J box and extend the circuits to the new panelboard location.

NEC doesn't allow for more than one circuit to supply power to an outbuilding. I assume you people are in the US. You really need to give a location when asking electrical questions.
 

toplessHO

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NEC doesn't allow for more than one circuit to supply power to an outbuilding. I assume you people are in the US. You really need to give a location when asking electrical questions.

NEC code reference please.
since when is a sub panel not allowed?
 
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pattenp

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NEC code reference please.
since when is a sub panel not allowed?

Sub-panels are allowed in a detached garage. I'm not talking about branch circuits from a sub-panel within the detached garage. I'm talking about the branch feeder from the main dewelling to the detached garage. There is to be only one source of power serving an outbuilding from another building. NEC 225.30
 
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Dusty Floor

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Feb 20, 2011
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To be clear, the existing setup is a single 120/240 3-wire feed from the main building. It has a single 120V circuit on each leg.
The breakers are actually 20A; the etching on the handle isn't visible under the normal light in that area but can be seen with a flashlight. I got the 10 from a glance at the printed "10 000 AIR" on the label, where the 000 are very tiny compared to the 10.

I'll take a look at going to 50 or 60A when we run trench the driveway; it makes sense.
 
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Dusty Floor

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For a minute, I was thinking I might be able to use tandem breakers to buy a little time on this project, but there's only one spot open on the neutral bus, so I could put at most one tandem in.
 

pattenp

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When you replace the feeder to the garage it needs to be 4 wires for 120/240 (2 hots, 1 neutral, 1 equipment ground).

You can use a tandem if the panel accepts tandems. Tandems don't fit in all panels.
 
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