I am looking to add power to my out building. It is 100/120ft from the main service box. The service box is a 200a service, and the total of the breaker installed is 230. There are plenty of extra slots for breakers to be added. I am wanting to run 2circuits to the building. #1 will operate 2 flourecent light fixtures, about 2ft long, a motion flood light with 2 75w bulbs, a work light on my shop bench with 100w bulb, and 2-3 wall outlets for charging cordless power tools.
#2 will be for my air compressor (small craftsman 25gal) a small window ac unit, and a 130 mig welder. (only one of these will be used at the time)

I am curious of what wire size to use, and size of the breaker.

I have a few hundred feet of 12/2, and 14/2, but just not sure what I should use on a long run like that.

Thanks!

Jeff

I think you'd probably do better with a true subpanel than running individual circuits. The length of the run and the startup demands of the compressors alone tell me that you'd probably be pushing things with 12/2 and voltage drop.

Can you provide some more information?

1. Does the compressor or MIG require 120 or 240?
2. What are the amp ratings on the compressor, a/c, and MIG units?
3. Is the wire you have rated for direct burial?
4. Do you ever see the need for more service?

It's a little more upfront cost to do the subpanel but it will allow you to upgrade in the future. Also, all it takes is one time forgetting to turn off the a/c when the air compressor kicks on and you're running back to the house to reset the breaker.

Quote:

---

Originally Posted by medic-dan

I think you'd probably do better with a true subpanel than running individual circuits. The length of the run and the startup demands of the compressors alone tell me that you'd probably be pushing things with 12/2 and voltage drop.

Can you provide some more information?

1. Does the compressor or MIG require 120 or 240?
2. What are the amp ratings on the compressor, a/c, and MIG units?
3. Is the wire you have rated for direct burial?
4. Do you ever see the need for more service?

It's a little more upfront cost to do the subpanel but it will allow you to upgrade in the future. Also, all it takes is one time forgetting to turn off the a/c when the air compressor kicks on and you're running back to the house to reset the breaker.

---

They are all 120v. The compressor has no info on it, but does have an extension cord warning. (12ga+ @50ft) The welder only says that it's 15a circuit rated, and the ac unit has no info on it. I'm planning on using a 3way carling master switch to power the units. That way only one can be on at the time. I will have to turn the switch to the appropriate setting to use each unit. That was how I planned on getting away with using them all on one circuit.
I could do a sub panel, and actually thought of a power feed to the building with a panel there. I don't see a need for any expansion of the service I have now. The wire will be ran in conduit that is already been buried. I had the guy use 2" to make it easy to add more wiring, like cable coax, and the feed for my security camera DVR.
I had an electrician come and start the job, but never came back. That was a year ago, and all he got done was the conduit from the house to the building.

I'm not an electrician but occasionally help out a Master when he needs someone to pull wire, etc. I don't think you'd need to upgrade the service to put in a sub panel. It's the way to go.

You can't run romex in conduit, expect where it might get damaged. In any case, the wire would have to be rated for underground as moisture can accumulate in the conduit. You're actually looking at THWN wire or equivalent. If you have 2" conduit you can easily pull in 4 conductors to run a subpanel.

The warning on the compressor is valid. You'll need much heavier wire for the distance you're running.

See what others suggest but I'd probably run #6 or even #4 out there. That would be good for 55-70 amps. Put in a 100amp panel, you don't have to put a breaker in with that high of a rating supplying it. It'd reduce the voltage drop on your run and that is mostly what you need.

If you can convert the compressor to 240, that't be a bonus.

One last thing, you can not run cable TV, low voltage, or telephone in the same conduit. You'd need another run.

Hope this helps

It's best to put in a sub-panel. You can use UF and direct bury the wire 18" or more deep. You should have a disconnect. Required if there are more than 6 circuits. A ground rod will be needed as well since this is a detached structure.

It will probably be cheaper in the long run, It's a misconception that the breaker totals must be less or equal to the main.

Motor loads at long distances do require a bit more finese to get the wire size right.

I suggest running 4 - #2 Aluminum with XHHW insulation and 1 - #6 Al XHHW. In the 2" PVC conduit. Less expensive, easy to install, will keep voltage drop low, best bang for the buck.

If you only ran one conduit, your screwed, as Medic mentioned, only power wiring in conduit, cannot mix other systems, no matter what kind of wire is installed.

And kiss is right, use a 100 Amp subpanel with a main breaker, 100 amp will be fine, at both ends.

The air compressor is not the heavy load, the AC unit and welder is thou.

TK
Could you tell me why 5 wires?

Probably because he (tkrussell) was thinking in 3 phase;) L1, L2, N, and G is 4 wires.

You can even use a 100 A breaker at the main panel to feed the sub and have the sub have a 125 A breaker. The sub-panel's breaker size can be greater than the feeder breaker. The feeder breaker must protect the wiring.

Yea Sorry, 3 #2. I do 3 phase every day, gets stuck in my head, and typing fingers.

WOW!! That's a good bit to take in. The alum. Wire sounds like a good idea. The cheaper I can keep it the better. So I need the wire from the panel, to the fuse? to the sub panel, then out! Now how do I connect the wiring to the main panel? Do I use a 100a breaker, or tie into the output of the 200a breaker for the panel, or what?

WOW!! That's a good bit to take in. The alum. Wire sounds like a good idea. The cheaper I can keep it the better. So I need the wire from the panel, to the fuse? to the sub panel, then out! Now how do I connect the wiring to the main panel? Do I use a 100a breaker, or tie into the output of the 200a breaker for the panel, or what?

You put a 100 A breaker in the main panel. Aluminum requires an anti-oxident coating on the wire.

That can go to a "main breaker" sub-panel (100-150A) or so.
You'll have to buy a ground bar kit for the panel and remove the neutral to ground bond screw. You'll need to install a ground rod.

Usually a secondary breaker maxes out around 100A.

OK so
200ft of 4ga alum.
100ft of 6ga alum.
100a breaker for the main panel
100a sub panel
Ground rod
100a breaker for sub
15a breaker for AC
15a breaker for Compressor
15a breaker for Welder
15a breaker for lights
15a breaker for receptacles
I can use the 12-2 I already have for the circuits

That sound about like what I need?

I figured that if I'm running a sub panel that I may as well just make them all separate circuits.

OK so
200ft of 4ga alum.
100ft of 6ga alum.
100a breaker for the main panel
100a sub panel
Ground rod
100a breaker for sub
15a breaker for AC
15a breaker for Compressor
15a breaker for Welder
15a breaker for lights
15a breaker for receptacles
I can use the 12-2 I already have for the circuits

That sound about like what I need?

I figured that if I'm running a sub panel that I may as well just make them all separate circuits.

Looks good.

You could use 20a breakers if you want. 12-2 is rated for it and might reduce some nuisance trips on the compressors and mig.

Add:

Ground bar kit (for sub-panel)

A couple of things...

Check the length, you said 100/120 feet to the shop from the panel, don't want to end up just a little bit short.

You can usually buy a main breaker panel kit with a 100 amp main in it and usually get 5 branch breakers for a decent price.

Check a real electrical supply house for your wire, it is almost ALWAYS cheaper than the big-box stores and they'll probably cut your conductors to length.

You'll need some GFCI's out there as well.

Questions on 2008 NEC:

KISS or TK doesn't he need 4 conductors per 2008 nec to the detached shop? Especially as he's considering bring in phone/cable at some point.

So it would be 300 feet of 4ga aluminum for the 2 hots and 1 neutral conductor and 100 feet of 6ga aluminum for the ground?

Yep, your last statement is correct 300' of 4 awg.
GFCI's for the recepticles.

You'll also need #6 ground for the ground rod and clamps and possibly a terminal.

Now's the time to either run a separate conduit for low voltage stuff or put in a couple of CAT5 circuits and a couple of RG-6 circuits as direct bury.

Never know when the IP security camera or alarm system will show up and the plasma TV and telephone. Heck, why not an intercom.

I can actually do the telephone with a wireless piggyback system, as well as the DVR for the security system. I'll double sheck my lenth's of wire by pulling a 3/8" rope through the conduit. I may do the wireless intercom too. Not sure I like my wife having me on a push button though. ;)

The aluminum anti-oxidation paste.