dakuda

I am going to be running 100A to my garage from my 200A house service. The whole house and garage used to run on 60A, so I figure I can spare some to the garage as needed.

My problem is, the garage is ~50 feet away from my house. I figure I will need about 75 feet of wire. What size should I run so as to not lose half of it on the way to the garage? I have a few welders and an air compressor that need 220V out there.

I plan on putting in a double pole 100A breaker in my existing panel and then running it to a 100A panel in the garage.

Parrothead

You don't have to worry about voltage drop, 75 feet isn't far. You need #3copper, or #2 aluminum. If you can find it, you can use 2-2-4 aluminum, which is the three conductors you need already bundled together. If you use aluminum, which I would recommend, cuz copper is insanely expensive, you need to lightly coat the exposed wire with an anti-oxidizing compound. You can get small tubes of it at the local big box stores.

Is this an attatched garage or detatched? If it is detatched, you need to drive two ground rods and use a #6 ground wire. If attatched, just run the ground wire from your service panel to the subfeed in the garage with the other conductors. Hope this helps.

speedy petey

Detached or not, you should run a ground WITH the circuit conductors. This is required in all but a few cases.
You can get AL 2/2/2/4 URD cable to run in conduit to a detached garage, or #2AL SER cable, which is also 2/2/2/4, to run inside the house.