subpanel questions, wire size etc... newbie here

[chainfeed]

First thread on garage journal, so here it goes.....

I recently bought my first house... has an old 2 car detached garage which I will be rebuilding once I get done with some other projects.

The previous owner (my father), buried a cable from the house to the garage but never hooked it up, it reads - Shelnutt/Allen E30445 (UL) AWG 6 CU3 CDR with AWG 10 ground Type UFB 600 volts sunlight resistant

I'd like to install a sub panel in the garage, the house has a 200amp service, so I'm thinking 100 amp panel. I'll be running a 220v miller mig welder, large 50-60 gallon compressor that a friend is giving to me for 75 bucks , lighting and eventually a more than likely 3 phase cnc mill...

From what I've read this cable is only good for a 60 amp panel which would probably be enough for the welder, compressor and lighting although most def. not enough for the cnc.

Advice?

 

[Gooch]

First thread on garage journal, so here it goes.....

I recently bought my first house... has an old 2 car detached garage which I will be rebuilding once I get done with some other projects.

The previous owner (my father), buried a cable from the house to the garage but never hooked it up, it reads - Shelnutt/Allen E30445 (UL) AWG 6 CU3 CDR with AWG 10 ground Type UFB 600 volts sunlight resistant

I'd like to install a sub panel in the garage, the house has a 200amp service, so I'm thinking 100 amp panel. I'll be running a 220v miller mig welder, large 50-60 gallon compressor that a friend is giving to me for 75 bucks , lighting and eventually a more than likely 3 phase cnc mill...

From what I've read this cable is only good for a 60 amp panel which would probably be enough for the welder, compressor and lighting although most def. not enough for the cnc.

Advice?

the ground is only good for 30 amps so the hots and Neutrals are only good for 30 amps. Ground needs to be of the same size as the hots until the ground wire size exceeds No. 8 IIRC(Code book is at work.)

Good luck getting the power company to install(and if they do get ready to pay, you'll have to pay for the two or three transformers) a 3 phase service at a residence.

 

[chainfeed]

i wouldnt expect them to put in a 3phase service, some machines will run single phase but I'll probably have to run a phase converter.

 

[Stuart in MN]

I believe that cable is good for 60 amps. Per NEC table 250-122, a 60 amp circuit can use a #10 ground wire.

edit: as others have pointed out, since this cable is UF it's rated for 55 amps.

 

[Gooch]

I believe that cable is good for 60 amps. Per NEC table 250-122, a 60 amp circuit can use a #10 ground wire.

that could be, i can't remember off the top of my head if it's the hot or the ground that needs to exceed #8.

 

[Ford12508]

Either way, #6 wire is only good for 50Amps, so he would not be able to do more than 50A, even if the ground is good for 60A

 

[Charles (in GA)]

NEC 310.16 says #6 UF Copper is good for 55 amps.

Charles

 

[Jduck]

I recently did this and used all #3 wire for the mains and #6 for the neutral and ground. This was for a 100 amp panel. Think about it, is it worth the 100 bucks your gonna save to always have to worry about it burning up or popping breakers all the time?

 

[chainfeed]

How about buying the 100amp subpanel and just running a 60 amp breaker for the feed from the maine panel, that way if I ever need to upgrade I'll just have to get the 100amp breaker and the larger wire?

 

[racer12306]

I think a bigger question is what kind of a load do you have in your house?

If you have a full electric (ie. HVAC, stove, water, etc, etc), I don't think it would be a good idea to run 100A out to a garage from your main panel. I don't know the code verbatim but I think there is a limit for subpanels, may want to look that up too.


I have a 100A house panel. I plan on running 40A to my shed. I essentially have lighting loads in my house only, except for spinning the washer, dryer and HVAC blower. In the shed the biggest load will be an intermittent air compressor, for the most part it will be lights.

 

[chainfeed]

Good point, the house has...
-natural gas fired hot water heat, no pumps
-natural gas stove/oven
-washer/dryer
-town water, so no pump there either
-no central air and I am too cheap to even use a window unit unless its 3985485 degrees out

Should I look into getting the garage its own service? I probably won't be able to pull enough power from my house once I get the cnc in there on top of the compressor and whatnot.

 

[racer12306]

I think that would be the better route. Do it all in one shot rather than spending money and then undoing it later.

 

[chainfeed]

any idea of cost on something like that? Do they run another wire from the street? the wire to the house comes in on the same side as the garage. Even if it was necessary to run a new line its only 40-50 feet to the pole from the garage.

 

[Falcon67]

You've got plenty of spare power in that 200 amp panel IMHO. We use similar equipment with a 2.5 ton AC/heat unit. The house runs on a 100 amp panel with a 60 amp feed to the shop panel (which is a GE 8/16 circuit 125A rated panel). You should be able to run 100A to the garage and not hurt the house. The dryer is your biggest load LOL. In my 60A shop there is a 60 G compressor, lathe, 3 phase mill/drill, A/C, 220V heater, welder, etc, etc, etc.

I would not run separate power to the shop until you check with the utility about how it's billed. I had a pole drop and separate meter for a bit because the power pole in the alley is like 20' from the back of the shop. Here in Texas, the PUC allows them to bill second meter at commercial rates. You donna want that. Once we discovered the billing issue, it was MUCH cheaper in the long run to re-run the shop feed and power off the house.

 

[Charles (in GA)]

I don't know the code verbatim but I think there is a limit for subpanels, may want to look that up too.

Common misconception, there is no limit on the max you can feed from one panel to another, so long as the wiring is protected by a properly sized circuit protection device (breaker/fuse).

Should I look into getting the garage its own service? I probably won't be able to pull enough power from my house once I get the cnc in there on top of the compressor and whatnot.

You may or may not be able to do this, or afford this. Some power companies, and some AHJ (Authorities Having Jurisdiction, ie, the building inspector/local codes) do not allow two meters on a single family residential property, probably to prevent subleting, renting, etc. If they do, the power company may want to charge commercial rates for the non residence meter, or charge the proverbial "arm and a leg" to run the cables, upgrade the transformer, etc. If you feel you will be using lots of electricity in your shop you might consider a new 320 or 400 amp meter socket on the house with dual feeds, one to the house panel, one to the shop. This too will cost.... alot, but save in the long run, as you won't be paying two meter base charges (like I do).

How about buying the 100amp subpanel and just running a 60 amp breaker for the feed from the maine panel, that way if I ever need to upgrade I'll just have to get the 100amp breaker and the larger wire?

This is a good idea and compromise. So long as the cable supplying the panel is properly protected, it really doesn't matter how large the panel you install in the garage. I'm a bigger is better person when it comes to stuff like this. I installed a 40 space/40 breaker panel in my shop, it isn't half full, but its there if I need it. Since your cable is already installed, use it.

Charles

 

[Grumpy365]

Good luck getting the power company to install(and if they do get ready to pay, you'll have to pay for the two or three transformers) a 3 phase service at a residence.

Not necessarily. I got them to put in 3 phase at my residence at no cost.

You do have to submitt a load schedule.

I had it approved, and then backed out, after I found out how limitted residential AC units are. The Residentail AC market didn't keep up thier 3 phase product lines.

 

[Aceman]

I'd call the power co. first, it only takes 5 mins. and see what your options are for a second service.

It sounds like you have plenty of ampacity left in your house panel if the power co. option doesn't work out. But I'd definitely try that first.

 

[chainfeed]

I'll give them a call today and see what the deal is.