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awg size for 60' underground line from house to shed for 60 amp

awg size for 60' underground line from house to shed for 60 amp

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Old 06-09-10, 08:14 AM
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awg size for 60' underground line from house to shed for 60 amp

problem:
I have a shed that is about 50 feet away from the house, and about 60 feet away from the main circuit breaker. Currently UF-B 14/2 with ground underground cable is drawn from the circuit breaker to the shed, while 12/2 is primarily used in the shed.

I'd like a subpanel in my shed for 60 amps. This way I could have a couple 20 amp recepticals for my saws, 15 amps for my lights, and have room for 220v 20amp lines in the shed for my compressor and perhaps a future 220v upgrade of my table saw.

Now I know I can't do that with the current setup.

Questions:
1) What size awg would I use for the underground wire? Typically I know 60 amps require 6 gauge but does this still apply for 60+ feet? I cant seem to make sense of this issue.

2) does underground cable support higher amp rating than interior cable? I can't make sense as to why the prior owner ran 14/2 underground then in the shed used 12/2 for all the recepticals and lights.
 
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Old 06-09-10, 08:44 AM
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Number 6 UF is fine for your distance. It is actually rated 55a but since there are no 55 amp breakers you can round up to 60a. Distances less then 100' do not normally require up sizing of the wire. You must use three conductor and drive a ground rod at the shed. Neutral and ground separate at the shed. Neutral is not bonded to the panel. See: http://forum.doityourself.com/electr...-drawings.html for more info.
 

Last edited by ray2047; 06-09-10 at 09:07 AM.
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Old 06-09-10, 09:13 AM
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If your going to use UF wire then you'll need 6-3 With/ ground as your wire. At 60' you shouldn't have a problem.

Jim

 
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Old 06-09-10, 09:23 AM
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Originally Posted by Capslock View Post
does underground cable support higher amp rating than interior cable?
Not in this case. The previous owner was probably ignorant of the code or had extra materials from some other project.

Your new feeder will need to be buried 24" if you use #6-3g UF-B cable or 18" if you use PVC conduit. A ground rod is required at the shed.
 
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Old 06-09-10, 10:15 AM
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I have huge boulderesque rocks below the ground, definately less than 24" below ground. It's a property of the geography of my area.

What would one do to bury cable with this type of restriction?

What would one do about the grounding rod?
 
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Old 06-09-10, 10:30 AM
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You have two options for shallow burial (depths are measured to the top of the pipe):

1) Use PVC conduit at least 12" deep and pour a minimum of 2" of concrete over the pipe at the bottom of the trench.

2) Use threaded metal conduit (IMC or RMC) buried at least 6" deep. Rigid conduit is more expensive and difficult to work with, but it does provide the protection required for shallow burial. Most home centers and hardware stores can cut and thread the pipe for you for a small fee when you bring in the measurements.

Since you'll need conduit for the shallow feeder, you'll want to use individual conductor THWN wires instead of UF-B cable. The conduit can be 3/4" trade size.

Another option would be to go aerial with a mast at the house and one at the shed. Most people don't like the look of that, but I'll mention it as a possibility.

One more option would be to try to find a path with the trenching machine. It doesn't have to be straight. If you hit a boulder, back up a few feet and try to navigate around it. You might really dig up the yard but may save hassle with the shallow trench. I still would recommend against direct burial cable in rocky soil though, especially in areas that have freezing temperatures. The rocks move around underground and can pierce the cable. I strongly recommend a conduit installation.

The ground rod may be driven at up to a 45 angle to avoid rock. If you have access to a hammer drill, you can use that to drive the rod through difficult soil. If you absolutely can't drive the rod there are some other legal grounding options we can go over if that's necessary.
 
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