What size circuits to feed my subpanel?

[Joel 67]

I am still in the process of learning as much as I can and planning out all the details before I start any work. I'd like to run a subpanel from my main 200A panel to my attached garage. The length of the run would be less than 40'.

These are the types of circuits I'd like to have in the garage

240v 30a circuit for compressor.
2-3 120v 20a circuits outlets around the garage
2-3 120v 15a circuits for CFL lighting
possibly a circuit for a natural gas heater of around 75k BTU

What do I need to have this capacity and keep costs down? How big should the circuit that feeds the subpanel be? I am hoping it could be under 100A and possibly as little as 60A since all these things won't be running continuously?

Thanks!

 

[tfi racing]

You could get by with a 30A service out to your garage,but for only a few dollars more and the same amount of work you could have a 60 or 100A service.I wouldn't waste my time with anything under 60,and for such a short distance the larger conduit and wire is not a huge increase to put in the 100.

 

[paranoid56]

i just did that with almost the exact stuff LOL (not the heater)
i did 6 3 romex and a 60amp braker on the main box. ran it to the sub box and wired it up. just finished the other day and its working great.

 

[Aceman]

I'd probably just run 6-3 Romex on a 60 amp breaker. Since your garage is attached you can use a main lug panel rather than the main breaker type. That'll save you a little.

 

[tfi racing]

Ooops-thought it was a detached garage 40' away from the house.Since it is attached I would go with Aceman's suggestion.

 

[Gary S]

If you have a Menards near you, consider buying a 100amp panel. They sell the 100amp panels with 20 spaces for $50. And, that $50 includes the breakers you need for the garage. Then you can wire it for 60 amps if you prefer and put a 60 amp breaker in your main panel, or if you spend the money for 100 amp wire, you can go for the full 100 amps.

 

[Joel 67]

Thanks for the replies. Is it correct to state that the sum of the individual circuits do not need to be less than the amperage of the sub panel? By my count these circuits add up to around 135-160 (depending on the heater needs). Or does the total amperage not matter so much as the max amperage of any given circuit? In other words, as long as all circuits are under 40A, then 40A is all I need?

I like the idea of having extra capacity but I think that cost wise, the wire gauge required for a 100A is a lot more than it would be for a 60A, correct?

 

[Gary S]

Thanks for the replies. Is it correct to state that the sum of the individual circuits do not need to be less than the amperage of the sub panel? By my count these circuits add up to around 135-160 (depending on the heater needs).

Correct. And, when you add the breakers, remember that a 60 amp panel would be 60amps at 240, so the 120 breakers count only for 1/2 of their rating if compared to the rating of the panel.

I like the idea of having extra capacity but I think that cost wise, the wire gauge required for a 100A is a lot more than it would be for a 60A, correct?

Yes, 100 amp wire would be significantly larger and costlier than 60 amp wire, but either way, you need to purchase the correct breaker for installation in your main panel, and the 60a breaker would cost the same as the 100a breaker.

If you don't plan on heavier use than what you have listed above, 60amp service should serve you very well.

 

[Falcon67]

It'll be some more, but not a great deal. The 2/0 cable I just bought for our service entrance was about $2.10/foot. I think the #2 I bought recently was around $1.50/foot. IIRC, #2 would be about 90A for that length run (check first). Yes, the sum of the breaker ratings can/will exceed your feed. As long as there is a properly rated overcurrent device in the shop feed, you'll be good. I use a "125A" panel on a 60A feed. It's good to have circuits broken out into several sections. Helps distribute the load and you can service a section easier. I use a separate run for any heavy duty machine, most of which are 220 runs anyway. I'm up to three, max should be four.

 

[Joel 67]

Thanks for the replies guys!

If #2 is $1.50-2 / foot, and my run is around 30', I'd need 90' total correct (2 hots and a neutral)? If that is the case I'd probably go with the #2 and whatever amperage it could give me (based on local code). Would that plus a ground all fit in 1.5" conduit?

 

[Gary S]

In addition to the 3 conductors, you will also need a 4th smaller wire for ground. The Code book will tell you what size the ground needs to be.

To save your sanity, I'd put in 2" conduit. It costs about the same as 1.5" and the wire pull is much easier. I used 2" for my run to make it easier.

 

[Aceman]

Why would anyone want to go to the trouble of running conduit to an attached garage? That's why they make cable....

If you want larger than #6 Romex, you can go with #2 AL SER. It has 4 conductors and you can breaker it at 80 amps.

 

[FastEddieG]

Joel, I'm going through a similar process in putting a subpanel in my garage. I am enjoying seeing other people's situations such as yours and the advice they are receiving. Thanks to everyone taking a few moments to post.

Why would anyone want to go to the trouble of running conduit to an attached garage? That's why they make cable.....

I'm no electrician, but wouldn't local code dictate that? It would make selling the house (home inspection and subsequent remediation) difficult and expensive if code only allows <6' in romex, bx, greenfield, outside of conduit, such as what I believe our local codes are in the SW Chicago burbs?

-Ed

 

[sberry]

Most places follow the NEC pretty well, Chicago may still be one that has its own scheme. Outside of there and one or 2 other places an approved cable would fly.

 

[Falcon67]

Also note that copper prices tend to float. It's kinda down right now, due to housing starts being down. If housing takes off, watch the prices shoot up quick.