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Old 08-22-2011, 04:50 PM   #1
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Quick Wire Size Question


I am adding an addition to my house and am going to install a sub panel to service the addition.

My main panel in the existing structure is 200 amps. The sub panel is 100 amps.

My question is - what size feeder wire do I need from the 200 amp box in the existing structure to the new 100 amp sub panel? I am considering both aluminum and copper and wonder if there is a difference in wire size between the two.

BTW, the sub panel is about 30 feet from the main panel.

Any advice would be much appreciated.

Thanks!
Bill

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Old 08-22-2011, 04:55 PM   #2
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Quick Wire Size Question


#3 copper or #1 aluminum. What code cycle are you on?

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Old 08-22-2011, 04:57 PM   #3
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#3 copper or #1 aluminum. What code cycle are you on?
I don't have a clue. Let's assume the latest until I can find out.

Bill
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Old 08-22-2011, 05:02 PM   #4
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I don't have a clue. Let's assume the latest until I can find out.

Bill

Are you using conduit/pipe or SER cable? If a SER cable, are you going through insulation?
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Old 08-22-2011, 05:14 PM   #5
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Are you using conduit/pipe or SER cable? If a SER cable, are you going through insulation?
Most likely SER. No conduit or pipe. Not going through insulation, but am going through/recessed between 2 x 8 floor joists. One of the reasons I'm asking about copper vs aluminum is to potentially minimize the hole diameter cut-out for the wire bundle so as to minimize the structural impact the hole through the 2 x 8 will have. Someday I may insulate, but don't have too. How would that impact the wire size? BTW, this is a basement run vs an attic run from a temperature standpoint.

Thanks for the help!
Bill
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Old 08-22-2011, 05:33 PM   #6
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Quick Wire Size Question


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Originally Posted by leeave96 View Post
Most likely SER. No conduit or pipe. Not going through insulation, but am going through/recessed between 2 x 8 floor joists. One of the reasons I'm asking about copper vs aluminum is to potentially minimize the hole diameter cut-out for the wire bundle so as to minimize the structural impact the hole through the 2 x 8 will have. Someday I may insulate, but don't have too. How would that impact the wire size? BTW, this is a basement run vs an attic run from a temperature standpoint.

Thanks for the help!
Bill
For the same amperage, copper is smaller than aluminum.

Under 2011 NEC rules, SER can be rated at 75C degrees if no insulation.

2008 NEC limited it to 60C degrees only.

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