House and Shop on 100 AMP Service

Question

I'm looking at buying a home that only has a 100 AMP service. I would like to have a small woodworking shop in the basement, but am worried that this will be too much for the service. While upgrading the service wouldn't be very difficult, it is an older home so pulling a permit would be a nightmare.

As for what is in the house. It has all gas appliances (oven, range, furnace, water heater, dryer) The major electric appliances are two fridges, the air conditioner, a whole house fan, a dishwasher, and a coffee maker. A lot of the appliances I can choose to run or not, but I'm concerned about the AC and fridges that may kick on periodically without my knowledge.

As for the wood shop, I can wire a lot of the equipment 220, so that should help. And I will only every be running two things at a time (dust collector and whichever other tool).

How much trouble should I expect with this setup. Has anyone experienced anything similar?

Answer 1

It depends on how big the house is (which in turn determines how many lights and other fixtures are present, as well as how big the HVAC is), how good you are at turning things off when you're not using them, and how big the shop equipment is. If you've got a 20-30 A table saw and a 20-30 A dust collector, that's close to (or more than) half your service right there. Throw in some lights, a fan or small heater, etc in the shop and you're over 50 A.

That said, if you're in the shop, that means you're not elsewhere in the house. So, no lights on, no TVs, etc, which reduces power consumption in the rest of the house. Fridges are pretty low-power these days. Computers can be high-power, but not when in stand-by or otherwise not in use.

A lot of people recommend at least 60 A when putting in a subpanel for a woodworking shop (e.g., The Wood Whisperer Marc Spagnuolo mentioned it somewhere, trying to find a link), which leaves you* 40 A for the rest of your house. Certainly, an AC unit in the South in the dog days of summer would consume all of that by itself.

It boils down to this: take the size of your HVAC breaker, add 10-20 A to it, and leave the remainder for your woodworking shop, as a rough estimate. You probably can't go for the big cabinet saw and super-duper dust extraction system, but even a 30-40 A shop would be plenty good for a hobbyist. Hell, a lot of us get by in a garage with no dedicated circuits!

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*True, you probably won't draw 60 A all of the time, even if that's the max your equipment can use. But, we'll assume so to be a bit conservative in our estimates.

Answer 2

ESPECIALLY with mostly gas appliances, I wouldn't worry about it. I have a small woodworking shop that I feed with a 60A feeder breaker and I have NEVER tripped it. What you have to remember is that if it's just YOU working in the shop, you are not going to be running more than one tool at a time, plus maybe a dust collector (highly recommended by the way) and some lighting. Homeowner type 240V single phase bench power tools are generally limited to 2HP, so about 12A at 240V worst-case scenario. It's not going to be a problem.

Answer 3

I ran a small shop on 60 amps for many years. Unless you're running welders, large compressors or other big electric motors (5+ HP) you shouldn't have any trouble. Even with my 13 amp table saw, dust collector and the random chargers and stuff I have plugged in I never tripped the main. Can't imagine fridges and A/C could account for more than 50 amps