Wire size for sub-panel

[Dick Thomas]

Aaron
I assume you will want 220V available in the garage. Usually the rating given for a panel/subpanel is it's max 220V input. A given panel can be used for a lower capacity, usually isn't, unless reserving space for future upgrades. If you want 100A of 220V capacity in your garage subpanel, then you need a 100A 220V breaker in the main panel, which will have a 100A breaker on each hot leg, which are mechanically tied together into a single unit. An electrician would probably run a 1/0 (One Ought) aluminum for 100A service.

If you want 100A of 110V service, then you could use a 50A 220V breaker in the main, with possibly 8ga, but more likely 6ga leads.

Strongly recommend you have a licensed electrician do this work, if only for the fact that 1/0 wiring is a bear to work with without the proper tools!!!

Good luck.

[Don Buck]

I second the previous comment about getting a licensed electrican to run the primary feed to the sub panel. This past summer I needed to get 100 amps to my detached shop about 25' from the house. I rented a ditch witch and had a 24" deep trench ready for the electrician. He came out prior and made measurements and brought out the materials (I believe 3/0 aluminum in conduit for the feed) and he installed a 100 amp breaker on my main breaker and energized the sub panel. Although not required, I had a main breaker installed on the sub panel. I agreed to be on site to help pull the 3/0 wire as it was very stubbon. Not including the rental for the ditch witch, I spend about $800 for parts (nearly 100' of 3/0 to go breaker to sub) and labor to get the sub box hot. I have been wiring the shop myself and have just one line to complete before I get it inspected. I never wired before but got a couple of good electrical wiring books and talked with several "experts" to gain knowledge and confidence.

I probably saved $800 running the circuits myself and by taking my time I have it layed out just as I want including outlets for a future air cleaner, 5 x 220v circuits for current and future equipment. I saved some additional money by getting a great deal on a used 125 amp breaker panel at the local Habitat for Humanity store for $10 and it was filled with breakers! My box has 20 slots and I've just about filled it out so a larger box would be highly recommended.

Good luck.

Don

[Brent Ring]

I ran 6-0 for mine. 100 AMP capable panel - 50 AMP main breaker. Not going to ever need more in this current shop