The 1st thing you want to do is check the load panel and see if the other spare breakers are marked 20amp. if so find the breaker that is being used for the garage and pull the wire out of that breaker and put it in one of the other ones marked 20 amp.
If you don't have one you can pull one of the breakers and take it to HomeDepot/Lowes and get a 20 amp. breaker, one you can pop in..that should help for just a little bit..
A good rule to go by is to walk around the shop and write down all the tools you have and write down the amps they pull that will give you a idea what kind of service you will need in the shop..then div. that by 2 ,because you will never have all them running at one time...but this just a swag rule of thumb but do think down the road,,,a 220 volt drop to shop is nice, that will give you two 110 volt drops.in one so to speak..or if you get a bigger power tool you will have the power for it without a rework ...update...
You didn't say if the garage/shop is next to the house if so it will be easy to get more power/out lets to the shop BUT if not will need to update/drop to the service to the garage..
Some of the old homes have just two wires running to the garage and you need to update that..
It's always best to over update ,that's to say a new load center panel (breaker box) to a 200 amp. service...but this will take a new elec.permit you can pull the permit as a home owner but you may want to call a lic. electrician to check it out and give you and hand...
I should note you can do it all it's not hard it just takes a bit of home work.
BUT the bottom line,, it just maybe wire size ,you said the lights would dim, that's a real tip off the norm..that the wire size is to small..
Think of like a water line,, 1/2" line it can only let so much water run but if you use 3/4" water line ,all the water outlets have what they need...
So it maybe time to use the other Spare breakers you have and run some more wire to the shop...two 20 amp. lines should do the job for now.
Originally Posted by NortonChris
I plan on taking over half our garage (maybe more) for my new woodshop. I think I have plenty of space, but power is a problem. There is only one 15 amp circuit from the house and the lights dim when the Miter Saw winds up.
I know I'm gonna have to have more circuits run, but not sure if I need additional service from The Electric Company. My 120 year old house only has 100 amps, but I do have 2 or 3 spare breakers (1 15 amp circuit just running to the outlet in the crawl space).
Advice? I've just bought a router, jointer and planer so I'd like to spend as little as possible on this...LOL.