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I want to add a 100 amp sub-panel from a 200 amp main in an attached garage. It will be about 100 feet from sub to main. What gauge wire should I use? The sub panel is to hook up a 7.5 horse air compressor and a welder.

marked as duplicate by Tester101 Jan 10 '16 at 20:52

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The NEC provides wire sizing based on the type to be used and the application.

NEC wire size table http://www.diychatroom.com/attachments/f18/80150d1390137097-100-amp-new-barn-nec.jpg

But here is a useful question that's already got all the answers I believe you'll need:

What size wire should I use to feed a subpanel in my garage?

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