Wiring a small garage/shop?

[rmorey]

I hope to expand my two car detached garage to make room for a more permanent dedicated shop. As it is now I have most all of my wood/metal working tools on casters. I can still get the wife's car in the garage but it would sweet to have the best of both worlds. I now only have 110v hard wired with limited outlets. I am running a long heavy extension cord from the dryer outlet to serve 220v for my compressor and table saw. I have a 110v/220v welder that needs more juice and appropriate plugs... so....

What do you all recommend for power into a small shop? Will a 50amp aux service panel be enough? Already have one for my hot tub. What is code for amount of circuit breaker total amp vs. service panel capacity? My service panel is 200amp. Can I exceed that with individual breakers added up?

I installed a 60amp breaker in my main panel which feeds a 100amp service panel in the shop. (removed the bonding screw) Got a deal on the panel. Seems to work ok. Put in 20 amp circuits for the tools. Less likely to blow when the tablesaw is working hard.

 

[newbury]

For a 1 man hobby shop, 100A is pretty good. For the most part at any one time, the most you would see running is the compressor, lights, a dust collector and one other tool. Maybe a heater or AC too, depending on season/climate. <snip>

Remember he's getting into welding, which can suck amps big time for a few minutes. Add in an A/C and ?

More important to me would be the change in cost for a bigger box. If I've got to pay $1,000 for a 60 amp service and $1200 for 200 amp I'd jump to 200 amp. Got to find the happy medium.

 

[Capricious]

I wired my own garage/shop many years ago. The main panel in the house is 200 amp, the sub panel in the garage/shop is 100 amp, but it is feed by a 50 amp breaker on the main panel. I ran a 240 volt compressor in there until I burned-up the motor. Currently run table saw, drill press, table sander, band saw, and so forth (not all at the same time). Biggest load currently is an old Marquette 240 volt/ 100 amp "buzz box" AC welder.

If I recall correctly (this was back in 1998), there was an issue with the main panel with pulling more than about 50 amps from one side without moving some of the loads to the other side of the panel, or some such.

NOTE: I am not an electrician. And so far, the place has not burned down.

 

[Gary Fowler]

I put in a 100 amp panel in my shop. It is a dedicated line with its own meter so it doesn't interfere with my 200 amp service in my house. I have a total electric home and it never sucks 200 amps, I cant see folks needing 400 Amp house service unless they are also running a commercial machine shop from their garage.
My shop has a 50 Amp breaker for my Miller 350 amp stick machine and it has never tripped. I only have about 10 circuits for 110v but have dual receptacles every 10 feet thru the whole shop. Just one of me so at most I might have the air compressor, welding machine and some lights running along with a possible 110V AC window unit Any grinders I run wouldn't ever be used when welding and when not welding just a fan runs on the welder. Never any problems with tripping circuits.

 

[PILOON]

You never know what can go wrong.
My shop has a small breaker panel that covers lighting and work outlets but my welder outlet is direct to the sub feed line.
The sub feed is properly protected at the main panel.
A short while back I flipped the welder switch on, sparks flew, acrid smoke developed and all lights went off in the shop.
The welder switch had simply collapsed and caused a dead short but fortunately I had sized breakers correctly to protect so the only downside was to air out the shop and reset the breaker at the main panel.
My update was to replace the welder switch with a switchable 220 v breaker switch as the factory unit is not to be found.
The moral is that you never know what can happen and there is no such thing as being over protected.

The welder switch, while not original, was ULC rated at 40 amps and never should have shorted.

 

[Gary Fowler]

As long as your breakers are sized to your wiring, nothing will cause a fire even if shorted like your welding machine. Oversizing your breaker because it trips to the extent that it causes the wire to heat up before the breaker will trip is what causes most electrical fires.
In Piloon's case the breaker did its job and tripped out causing nothing more than a little smoke at the shorted switch.

 

[GPintheMitten]

I like to size the main panel feeder breaker to exceed slightly the subpanel main breaker, like 150 feeder breaker in the main and 125 subpanel main... or 125 feeder breaker to 100 main breaker in the sub. That way when you are I the shop, if you ever exceed the subpanel, you can reset the breaker in the shop and avoid going back to the house.

This not likely with 125 amp or 100 amp box, but could happen if you size down to 60 amp or so.

Also make sure you size the wire for the feeder breaker and vice versa.

You might want to price out feeder breakers of various sizes for your main panel and see how many spaces they requure, and your space availability in your main. Check wire prices as well. There may be a price point sweet spot in there somewhere.

I personally would tend to go with 150 amp feeder in the house and 125 in the shop but that may be overkill for your needs.
You may want to go 125 in the hiuse feeding 100 in the shop.

 

[dstig1]

Remember he's getting into welding, which can suck amps big time for a few minutes. Add in an A/C and ?

More important to me would be the change in cost for a bigger box. If I've got to pay $1,000 for a 60 amp service and $1200 for 200 amp I'd jump to 200 amp. Got to find the happy medium.

Frankly, from what he has described, 100A is plenty, and even 60A would probably work. Like I said before, it is a bit silly to run a 200A subpanel from a 200A main panel... 100 or 150 is fine, but 150 is excessive from the sounds of it. Yes the incremental costs of upsizing tend to be smaller as the bulk of the job is finding a path and pulling the wire rather than the materials themselves (if you hire the job - if you don't, then this is reversed as your time is "free" and it 100% materials so upsizing costs a lot more proportionally).

It always helps to put a bigger subpanel box in that has more spaces. That at least allows you to dedicate breakers to certain items as needed. Even on a 100A panel, something with 20-24+ spaces is not a bad idea for the flexibility. It might be rated at 150 or 200A, but that is fine.. As long as the subpanel box is rated higher than the feeder, you are safe. Most subpanels I have done were main lug, without a main breaker. That would depend on the situation, but tripping a main breaker (either main panel or main subpanel) means you have BIG troubles going on. So I don't see the benefit to having main breakers on both ends of the wire unless you way undersized your subpanel for some reason.

I ran my shop off a 60A subpanel for 15+ years, never tripped any breakers, and I have some serious WW equipment.

 

[dragoneggs]

Thank you everyone for your comments!!! I guess I am thinking I should be in the 60 to 100 amp aux panel range. I am getting cramped in my 200amp house panel so I need to research what the feeder circuit will require for space and wire to the aux panel.

 

[MossRoad]

(forgive me in advance if you know this already )

And I'm not an electrician, so you may die if you do what I say... so take that seriously and get professional help before proceeding! :laughing:
With that said....

You already have 200amp in your house, but your panel is cramped. You are going to gain one single slot in your house panel when you pull out the 110 circuit for your garage. You will only need one aditional single slot in your home panel, so you can install a two pole breaker in the house panel to feed the garage with 220. The two slots have to be next to each other on the same side of your panel. You can move one of your existing single pole circuits to the other side of the box, or up, or down, to achieve two slots next to each other. If you don't already know, as you move down one side of your panel the first breaker is on one leg of 110, the one below it is on the 2nd leg, the one below that on the 1st, below that 2nd, etc... so when you put in a double pole breaker, it grabs both legs and you get 2 x 110 = 220. Again, forgive me if you already know this, but some folks don't. Then all you need to do is install a 50 or 100 amp breaker(whatever you choose) in your house panel to feed the garage.

You would probably want to run either direct burial cable or cable in a non-metalic conduit from the house to the garage and use the apropriate elbows, bends, grommets, etc... to make it watertight and safe to code.

In your garage, you will most likely need to install what's called a sub-panel. I would install a seperate disconnect switch in the garage ahead of the sub-panel, or you could just get a panel with main breakers in the top of it. Once you have that sub-panel in the garage, you can wire away safely if you pull the disconnect first. If the box has main breakers instead of a separate disconnect, the top of the box will still be hot.

Hope that helps. And have fun with your project.

Also, you mentioned your house panel getting full... you could always install another sub panel in your house to gain more circuits.