Sub panel wiring
 

Have a 100 amp sub panel in my garage. It was used for a backup generator, but ended up wiring for generator directly to main panel. I am running new outlets throughout my garage and was gonna use the sub panel for garage. I ran 2-20amp outlets on each of 3- 12/2 lines. Got 3-20amp breakers for those circuits. Also have a 15amp breaker already in the sub panel for garage door opener and lights. What size wire and breaker should be used to feed the sub panel?

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It's not quite that easy.

Do you want 100 amp service?

What loads do you expect to have in the garage? Do you plan to run any "heavy" tools? Welders or air compressors for example? Any 240 planned in the future?

A load calculation would help.

Is the garage attached to the house? How far is the cable run?

Short runs, attached to house, single car. Nothing major(air-compressor, drill press, grinder, etc.). Were no current outlets in garage and I needed some, so I put in a few. No 240 planned out of subpanel. Just the new 6- 20amp outlets and the existing 15amp breaker for opener and lights. Total of 4 breakers in subpanel. 3-20amp(new outlets) and the 15amp.

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100 amp sounds like over-kill. You can feed that sub as a 60 amp from your main or even less.

So should 10/3 wire be sufficient? And what size breaker? 60amp? Or could I go smaller?

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10/3 would give you a 30 amp main. You could do it and probably won't have any problems if you're only running a few things at a time.

You could up to 6/3 for a 60 amp main.

I'm assuming you want NM cable. No need for conduit.

Ok. Thanks for all your help.

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Don't forget, you need to separate the neutral and ground at the sub panel.

Remove the bonding jumper on the panel.

Yup. Neutral line to be insulated from panel and ground bar. Thanks

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