House main to shop sub pannel

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  #1  
Old 12-19-06, 12:42 AM
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House main to shop sub pannel

My question is will #6/3 UF/B direct bury be a large enough wire size to go from my main, with a 60 amp double pole breaker to the 100 amp sub pannel I plan to locate in my shop. I've had a friend or two tell me I should check on just putting a second meter due to the fact I've got to go about 200ft. from house to shop. I have done little more than get my pole barn/shop built and have it hooked up with a really long cord to run a saw and such along with a few flouresent lights, but I'm trying to get things moving along in the way of completion. I am trying to kinda pay as I go, and I'm working on the framing of a few walls so I'm not really ready to wire the inside yet. I for now just want to make sure I get the right guage wire, to make that 200ft. span. I plan on closing up a section of the shop kinda like a studio appartment with an a/c large enough to cool a well insulated 24x14 room. The shop as an eve height of 16ft. so the ceiling will be insulated as well. I will probably have a small fridge, mircowave, TV, and radio, (the Basic Dog House for me/kid appartment) along with a table saw, miter saw and stuff, but by no means a factory of mass production in my 24x36 building. I had it built 16ft. so the second floor could be an easily accessible storage area while I still have use of the building. So any ideas would be appreciated greatly. I read alot of post looking for idea's when it dawned on me I should just join this community of what seem to be very knowledgable tradesmen, and stop reading all the other post trying to find a solution. Thanks in advance guys
 
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  #2  
Old 12-19-06, 04:34 AM
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The answer to your question depends on how much current you really think you will need at the barn.

To pull 60 amps and stay within 3 percent voltage drop, you probably want 4 gage copper wires.
 
  #3  
Old 12-19-06, 08:13 AM
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I'll phrase the same answer a little different than Bob's.

If you stick with the #6UF, you can only pull 35A at 240V before exceeding the ideal voltage drop limit of 3%. While this is not a deal breaker, high voltage drop results in shorter lifespan of electric motors and very noticeable dimming of lights when motors start.

My recommendation is that you use #2-2-4-6 direct burial aluminum cable (USE) that is sometimes sold as "100A mobile home feeder cable". Feed this with a 60A breaker from your main panel. It will probably be cheaper than the copper, and can support up to 60A with an acceptable voltage drop of 2.7%. The bigger wire is a little more difficult to work with, but you only have to do it once. Also worth mentioning is that you need to pay close attention when you terminate aluminum wire on the breaker and panel lugs. Use a wire brush to clean the oxidation off the bare Al, and apply a lot of non-oxidation grease. Be sure to torque the lugs to the proper ft-lbs listed on the panel label; this is important for Al wire.

General Outbuilding Subpanel Advice:
You'll need to buy an add-on ground bar kit for the subpanel, and remove the bonding screw/strap to ensure that ground and neutral buses are isolated in the subpanel. Furthermore, you'll need to drive a 5/8"x8' copper ground rod at the outbuilding and connect it to the ground bus of the subpanel using and acorn clamp at the rod and #6 bare copper wire (Al is not allowed for this specific application). The garage subpanel requires a main breaker as a disconnect.

Edit: Just checked 2-2-4-6 Al USE is about $2.40/ft and 6/3 copper UF-B is $3.66/ft
 
  #4  
Old 12-21-06, 12:31 PM
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subpanel

check local codes if you can even use aluminum wiring. we can not use anything but copper, regardless of where/how it is ran... marty
 
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