Sub panel to attached garage.

[reinhardt]

Hello all,

Looking to pick some electricians brains. I have done some searching and havent quite found all the answers i am looking for.

first question: I have a 150 amp main panel, can i add a sub panel in garage? now for the facts...

1. Distance from main panel to planned sub panel is approx 60 feet through attic.
2. Have electric dryer, stove, water heater, and hvac.
3. I have two open slots for a 220 breaker.

Next question: How many amps do i need in the garage? here's what i want.....

1. overhead lights, approx (9) 4 ft x 2 bulb fixtures.
2. small air comp (110 volt)
3. window a/c unit
4. 20 amp circuit for outlets
5. over range microwave in kitchen (short run from garage to kitchen)
6. possibly whole house fan in ceiling of garage
7. maybe a 220 circuit down the road for a welding machine, currently have a 110 fluxcore.

if the 220 welder and whole house fan would overload what the main panel can support, i am thinking i could run wire big enough to support it in the future and install a sub panel to also support it but use a breaker of a lower value. then at a later date upgrade the main panel to support a larger sub panel and install the larger breaker at that point in time. i really want to avoid the expense of upgrading my main panel.


finally: what size conductor do i need to run?

i have read that i will run from main to sub: 2 hot leads, a neutral, and a ground.
is the wall above the main panel going to have to be cut open? i assume it will so i can clamp the cable into the top of the box.... dang. the walls in that room are textured, so i would love to avoid cutting them up. i dont mind cutting drywall out in the garage tho. thanks for answering my questions. i did a search before asking, but wasnt able to pull up answers specific to my situation.

 

[Aceman]

I would probably run #2 AL SER and breaker it at 80 amps. If you can cut a large enough hole in the top of the wall, you can clamp your connector on the cable first and send it down through your panel. Then just screw the locknut onto the cable clamp.

 

[portcity]

#1-yes, you can add a subpanel there. you can add just about as many as you want. I have 4 subpanels, inside, one to add additional slots, christmas light panel, and garage.

#2 & 3- depends on what you want. My father has #8 copper running 50' to a garage running 2x 220 welders, plasma, 6x 4' lights, mini fridge, 220 3hp compressor, and the receps. He never has a problem, because what is the chance of powering everything on at once. Im in the process of building my garage(finishing). I have a #6 copper running 90'. I am powering pretty much the same thing except the addition of a tanning bed. Now Im thinking about changing to a 100amp alum service wire to add ac and water heater. If I were to say, it would probably be better to just use a 100 amp service. You said a 20 amp recep circuit. I would say run a few different ones. wont cost much extra, and will help by not overloading that circuit. I like the idea I seen on here about running dual recep boxes and have each one on a different circuit. That way you can plug two things up there and not worry about overload.. You have to think, a good circular saw uses 15 amps. Now based on the 80% rule, you are close to the limit there. Add a big fan to that circuit, and its overloaded

 

[reinhardt]

so u all figure my 150 amp main panel will support adding a 80 amp sub panel then? if so, what is a rough ball park figure this is going to cost me in materials? thanks again.

 

[portcity]

roughly without checking current prices; conduit and supply line $120-200, sub-panel $50, 80 amp breaker $30, 250' of 12-2 $70. then figure your sub panel breakers, boxes, and receps; probably another $50-100. Of course this can very a lot, depending on what panel, size & type of wire, type of receps you choose. But this should give you a basic ballpark figure

 

[jvitez]

so u all figure my 150 amp main panel will support adding a 80 amp sub panel then? if so, what is a rough ball park figure this is going to cost me in materials? thanks again.

No one can tell you. You need to do an actual load calculation of your house, then add the wattage of whatever you might think you'll be running at the same time in the garage. Are you over 150 amps then?

If you're not, you then back calculate to get the garage subpanel size, not the other way around.

You should get the proper NEC load calculation for residential services, and go from there. Actual numbers will tell you with certainty.

 

[reinhardt]

No one can tell you.

You should get the proper NEC load calculation for residential services, and go from there. Actual numbers will tell you with certainty.

sounds like ur talking about love..... lol! u'll know....

anywho... where can i find the nec load calc? i really dont wanna spend $80 for a copy of the nec. do they have it at the library?

and maybe a book on how to use the nec? i scanned through it, and it was like reading stereo instructions....

 

[jvitez]

sounds like ur talking about love..... lol! u'll know....

anywho... where can i find the nec load calc? i really dont wanna spend $80 for a copy of the nec. do they have it at the library?

and maybe a book on how to use the nec? i scanned through it, and it was like reading stereo instructions....

I'm in Canada, so I bought a CEC guide for homeowners. Hopefully the US gents reading this can give you some help on where to find the NEC guide if you want a hard copy.

I did find this online calculator. Not sure how detailed it is vs. the "real" guide, but try this and see what you get.

http://www.zenfixit.com/load_calculations.shtml

 

[Charles (in GA)]

Depending on what you are doing in your shop or garage, generally, every thing you do is intermittent use, except for the lighting. If you have a large compressor and plan to run a blast cabinet, that becomes a consideration, or a smaller compressor and a 90 grinder or similar, but unless you are running a lathe, heavy duty welding or something else that draws lots of current, you can actually get by with a fairly limited service. I'm a big fan of putting in the largest panel you can, a 40 space, 40 breaker panel, this allows you to divide up your branch circuits any way you see fit, but truth is, you will be consuming very little current, and rarely two things at once. The lights and the fridge if you have one, but how often do you use the drill press, the compressor or the welder? Even if you are using the welder all day, its a little bit here, a little bit there. Drilling a hole, takes a, minute or two and you are done.

Its not a residence, so doing a load calculation is a little different.

Charles