Electrical subpanel

I have a 50 Amp subpanel in a shop that is 180 feet from my main. It is powered by two #2 aluminum and a #4 ground (also grounded at the shop), direct burial wire.
I now find that I would like to run a 50 Amp welder out there.
My question is: will the wire support a 70 Amp breaker or do I
need to look for another alternative?

 

If your absolutely sure that the entire length of wire is #2 AL, then it should be good for 70A. I wouldn't go more than that, given derating factors, because of the distance. I can't quote a exact amperage for that distance and wire gage becuase I don't have my NEC book with me at the time. Make sure the sub-panel has a high enough rating. (perhaps 100A?)
The #4 ground you mention, what color wire? White or gray? Is is the nuetral?
There should be a seperate grounding buss in the subpanel, connected to a grounding conducter going back to the main panel, it should be at least #10 for 50A, or #8 for up to 100A. Do you have a grounding rod at the subpanel? (I want to make sure the subpanel is bonded properly, for your safety!, as well as code.)

gj

 

Yes, the #2 aluminum goes the whole way.
(I once came across a wire size calculator on the internet but I haven't been able to find it again. Anyone know where that is?)
The #4 is the neutral (black) and yes i have a separate gounding buss in the subpanel that is connected to a grounding rod.
Thanks.

 

I'll assume it is a detached shop with no metal piping between the house and the shop. If so, you are ok with the #2 AL. The #2 AL is rated for 75A and you are permitted to go to the next size breaker if you choose, which would be as high as 80A. When the load is high in the shop, you will get approx. 3% voltage drop from the house to the shop, which should be ok.

 

http://www.codecheck.com/fundamental.../ampacity.html
is a conservative table to follow, they do not use the exception to take you to the next higher breaker.

 

I use a lot of alum number 2 and usually feed it with a 60 and it works fine for welding on. Some up to 200 ft. As green jacket eluded,,, if this is a 3 wire feed to the subpanel it does not need a seperate grounding buss,, in fact this is dangerous. It MUST be bonded to the neutral bar and also have a ground rod. There is no way to return a fault to the original panel without a bond and if a piece of equipment would short it could have a 120v potential without you knowing it until you touched it. A short will not trip a breaker without this bond. If it is 4 wire it is a different situation.

 

Okay, now I am confused. It is a 3 wire connection (plus separate grounding rod). Evevrything else I been told says that the neutral should not be bonded.

 

3 wire MUST be bonded, 4 wire is unbonded. Shorts must be carried back to the panel in order to trip the breaker. Read grean jackets first response carefully. There will be no debate on this forum about that. It is a fact not an opinion.

 

See http://www.homewiringandmore.com/hom...detgarage.html approx 3/4 of the way down the web site "PICTORIAL EXAMPLE OF A GARAGE PANEL WITH 3 OR MORE CIRCUITS 240 VOLT 60 AMP, 100 AMP, 200 AMP BRANCH CIRCUIT WITH OVER HEAD CONDUCTORS WITHOUT AN EQUIPMENT GROUNDING CONDUCTOR RAN WITH THE FEEDER SUPPLYING THE DETACHED STRUCTURE"

The neutral and ground must be bonded because during a fault, the current wants to get back to the neutral in your main panel, and that will only happen when the neutral and ground is bonded in this remote panel (you didn't have an equip. grounding conductor run with the subpanel feeder). Go to library and check the 2002 NEC Article 250.32(B)(2).

 

Thanks all! I think I've got it. (Just goes to show that you can't go by what the guys at the building materials places say.) You've also pointed me in the direction of some other useful info.