Garage sub-panel?

[King Nothing]

I need to get more power to my attached garage as it’s woefully underpowered right now (8 total outlets and 2 light sockets on a single 15a circuit). I only have 2 spots left in my breaker box which I’m trying to save for power when I finish the basement. I do, however, have 40 and 30 amp double breakers meant for an electric range and dryer that aren’t used because we have gas appliances. Can I repurpose that 40a circuit to run a sub-panel in the garage? Is a 40a sub panel enough for the garage assuming I want to have 2 20 amp circuits, the existing 15a circuit, and a 240 outlet? If 40a isn’t sufficient, how much amperage do I need?

 

[billconner]

If normal garage activities, no real high power gear, I'd put in a 60 amp panel so I or some future user could charge an ev and not have to turn the lights off.

 

[Terry D]

It all depends, is that 40 amp range circuit a 3 or 4 wire. If just a 3 wire, then no. You need 4 wires feeding a sub panel. 2 hots, 1 neutral and 1 equipment ground. If it is a 4 wire already, do you think 40 amps would be enough. What is your 240 volt outlet going to be for. I wouldn't run nothing less than 60 amps. You can use the space in your panel, replace the 40 with a 60 amp and run a 6/3 nm-b to the garage. It all depends what you are going to put out there. Always plan for the future.

You might want to change that 220 volt to 240 volt in your post.

 

[pizza]

unclear. repurpose the entire circuit (including wiring) or repurpose the slot that this 40A breaker occupies? do you mean this 40A dryer circuit goes into your garage where you want your sub panel? i'd put a bigger breaker and run new wire for a sub panel.

 

[King Nothing]

If normal garage activities, no real high power gear, I'd put in a 60 amp panel so I or some future user could charge an ev and not have to turn the lights off.

Can I pull the 40a range breaker and replace it with a 60 and run the appropriate wire off of that? My main breaker box is only 100a so a 60a breaker on there seems… weird

 

[pizza]

yes. it's not weird. count up the breaker capacities in your load center now. it's probably more than 100A.

you just can't draw 100A at any given time.

 

[billconner]

Good cautions. I assumed you simply had breaker space in main panel, and could install a new breaker and wiring.

 

[King Nothing]

It all depends, is that 40 amp range circuit a 3 or 4 wire. If just a 3 wire, then no. You need 4 wires feeding a sub panel. 2 hots, 1 neutral and 1 equipment ground. If it is a 4 wire already, do you think 40 amps would be enough. What is your 240 volt outlet going to be for. I wouldn't run nothing less than 60 amps. You can use the space in your panel, replace the 40 with a 60 amp and run a 6/3 nm-b to the garage. It all depends what you are going to put out there. Always plan for the future.

You might want to change that 220 volt to 240 volt in your post.

I dont know about the range circuit but I would unhook the range wiring from the breaker and run new wires to the garage. The 240 outlet will be used mostly for my table saw and maybe an air compressor. Possibly a small welder in the future. I dont know if 40a will be enough, that’s kind of what I’m trying to figure out here

unclear. repurpose the entire circuit (including wiring) or repurpose the slot that this 40A breaker occupies? do you mean this 40A dryer circuit goes into your garage where you want your sub panel? i'd put a bigger breaker and run new wire for a sub panel.

I want to repurpose the spot in the breaker box and run new wire to the garage. I guess I’m asking if a 40a sub panel is enough for what I want or if I need to go bigger, and wondering if I can go bigger being that my main breaker box is only 100a

 

[Terry D]

I would not go with anything under a 60 amp

 

[billconner]

Can I pull the 40a range breaker and replace it with a 60 and run the appropriate wire off of that? My main breaker box is only 100a so a 60a breaker on there seems… weird

Yes. Just did just that. I checked with my friends on CMP and electrical inspector said fine. Just have to find the correct breaker which usually isn't hard.

 

[billconner]

The sum of the breakers in most any panel is greater than the main. I had a 42 space panel in last house with 200 amp main, put an amp meter on it, and rarely over 30 or 40 amps. Gas appliances, no a/c, and all LED lighting. Electric heat and/or ac would justify calculating. On a 100 amp main, a/c or electric heat and an EV charger might push it.

 

[sparky 1971]

40 amps would probably be fine, but you're more than likely going to have to take new wire to the garage anyway. Pull a 6/3 nm, install a 60 amp breaker and be done with it. You could always land the #6 on the 40 amp breaker and know that there is a chance you might have to upgrade to a $25 60 amp breaker in the future. As far as the 100 amp main, you will be fine. There are a lot of homes out there with a 100 amp service that are running a lot more than you are. I would be surprised if you were drawing more than 30 amps total under normal use.