subpanel feeder


Old 04-25-01, 08:48 AM
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A great forum, very educational! I am building a garage with an upstairs woodworking shop, and the building will use a 60-amp subpanel for several garage circuits. I need to run an underground feeder about 120 feet in total length between the subpanel and the main house panel. Questions: What specification of wire cable should I request at my home center, and what size conduit is needed for it? Can I use a 60-amp breaker at the main panel for the line even if it is a 55-amp wire?

I do have a code book, but it appears rather confusing about these points. Thanks for your help.

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Old 04-25-01, 07:49 PM
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Greg...As a general rule of thumb in the electrical trade, you always increase one wire size for every 100 feet of distance to compensate for voltage drop. In your case I would use #4 copper which is good for 100 amps.(table 310-15(b)(6). Since you are running the wire in pipe, I hope, You can use pretty much any type of wire. If you go to a Home Depot, they will only have one kind to choose from usually, I think it isTHWN, gasoline?sunlight resistant and it will say suitable for SE (service entrance). So you will need 360 ft of #4 copper ($.35 ft)and a ground wire #8 copper(Table 250-122). I wouldn't put a 60amp breaker on a wire that can only handle 55 in my house even if it is allowed by code. Pipe size 1 1/4 pvc would be plenty big and would make an easier pull out of 120 feet.(Table C9) Pg.601 in the NEC.

I hope that helps, any questions [email protected]
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Old 04-26-01, 10:54 AM
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Location: Fayetteville, NY, USA
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Just as an alternative, you are permitted to use direct-buried cable. Under most circumstances for a dwelling property you need only bury it 18" deep. There are special rules about running under pavement, near swimming pools, etc. I'm not saying this is a better alternative, just an alternative.

For conduit, your best choice is probably schedult 40 pvc, and transitioning to schedule 80 when going up a wall on the exterior of any building. (80 is tougher, and often required by local code enforcement folks for added protection against such things as lawn mower collisions.

Hope that helps.


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