Feeding a pole barn from a subpanel

[ErikinMich]

This is a great forum, my first post. I am going to be installing electrical in my pole barn about 150 ft from house. I have a 200 amp service panel that is full in house with a sub panel next to it. The sub panel is empty so I wanted to feed my barn with it. I am running 100 amps 240V to the barn. #2 Cu THWN in 1 1/2" in shd 40 pvc.

I plan to run 4 wires, 3 - 2 Cu THWN (2 Hots and Neutral) and a 8 bare Cu for equipment ground. in 1 1/2" in shd 40 pvc. I have the ground and neutral isolated in the sub panel in the basement and plan to have the isolated in pole barn as well. Where would the equipment ground be connected in the basement sub panel, the ground bus ? That is what makes sense to me but wanted to make sure.

Thank you for your feedback.

 

[pattenp]

In sub panel all grounds go to ground bar and all neutrals go to an isolated neutral bar.

 

[sberry]

That is an expensive way to do it, alum wire is so much cheaper.

 

[pattenp]

I'm with sberry on the cost of copper. Have you done load calculations to know you actually need 100A? Aluminum wire is not the wire of years ago and is a good choice for long runs to save on cost.

 

[05wrangler]

Yep, land the equipment ground on the ground bar in both locations and all is good. You could also get by with using a #3 for your application as long as both breakers are 75degree C, which I'm sure they are. But a #2 is a fine choice as #3 is rated right at 100 amps at 75 degree C. Remember if you use aluminum you must apply no-locks to the terminations. Also no matter what wire you use but definitely with aluminum, torque your terminations to spec. Also the number 1 thing no body ever does and creates big problems down the road (over heating, termination failure, fire ) is number one. When stripped the wire, DO NOT cut into the conductor as it will score the soft aluminum and create a hot spot, number two, make sure you sent a maintenance schedule to service these terminations and retorque them. As they WILL expand and contract and loosen in the lug. If it where me I would just do copper and be done. But what do I know I'm just an electrician

 

[pattenp]

Yep, land the equipment ground on the ground bar in both locations and all is good. You could also get by with using a #3 for your application as long as both breakers are 75degree C, which I'm sure they are. But a #2 is a fine choice as #3 is rated right at 100 amps at 75 degree C. Remember if you use aluminum you must apply no-locks to the terminations. Also no matter what wire you use but definitely with aluminum, torque your terminations to spec. Also the number 1 thing no body ever does and creates big problems down the road (over heating, termination failure, fire ) is number one. When stripped the wire, DO NOT cut into the conductor as it will score the soft aluminum and create a hot spot, number two, make sure you sent a maintenance schedule to service these terminations and retorque them. As they WILL expand and contract and loosen in the lug. If it where me I would just do copper and be done. But what do I know I'm just an electrician

This is misinformation as the new aluminum alloy does not need be retorqued and should not be retorqued once tightened to spec. You must be an old electrician.

 

[sberry]

I got nothing against checking to see a lug is still tight. They don't want it to keep tightening and cut the wire. I use a little poo on them and a dab on the lug screws. That stuff is all fine thread, wantstobstick and if it sticks the day it's installed doesn't get better with time.

 

[05wrangler]

This is misinformation as the new aluminum alloy does not need be retorqued and should not be retorqued once tightened to spec. You must be an old electrician.

new aluminum is "compact" this is only sizing not expanding problems. If the manufacturer has recommended not re torquing then it is not needed. But no manufacturing is currently writing off maintenance torquing of their aluminum conductors. I am a trained and up to day journeyman wire men and also an instructor for the IBEW apprenticeship

 

[wyliesdiesels]

Yep, land the equipment ground on the ground bar in both locations and all is good. You could also get by with using a #3 for your application as long as both breakers are 75degree C, which I'm sure they are. But a #2 is a fine choice as #3 is rated right at 100 amps at 75 degree C. Remember if you use aluminum you must apply no-locks to the terminations. Also no matter what wire you use but definitely with aluminum, torque your terminations to spec. Also the number 1 thing no body ever does and creates big problems down the road (over heating, termination failure, fire ) is number one. When stripped the wire, DO NOT cut into the conductor as it will score the soft aluminum and create a hot spot, number two, make sure you sent a maintenance schedule to service these terminations and retorque them. As they WILL expand and contract and loosen in the lug. If it where me I would just do copper and be done. But what do I know I'm just an electrician

#2 is not needed and overkill.

No-locks? Never heard it called that. Anti-ox paste is only required when the manufacturer calls for it. Many dont.

Which NEC code says retorquing is required?

Re-torquing is not required and often causes over-torquing of the lug. The only way to re-torque is to start over by cutting the end of the wire off and torquing to spec again.

new aluminum is "compact" this is only sizing not expanding problems. If the manufacturer has recommended not re torquing then it is not needed. But no manufacturing is currently writing off maintenance torquing of their aluminum conductors. I am a trained and up to day journeyman wire men and also an instructor for the IBEW apprenticeship

You have it backwards. Unless the manufacturer says to retorque, then its not required.

Same goes for anti-ox paste.

I am Ibew as well. Retorquing is not something taught nor done around here. Its not required nor necessary.

Show me the code where its required!

 

[Bert_]

Maybe he means No-Ox?

I run aluminum whenever it's practical. Issues with aluminum are overblown, if you make a decent connection you will never need to worry about it again. Copper is a little more forgiving of sloppy connections, but it will burn up too if you don't get a lug tight.

 

[05wrangler]

Yes no-ox, auto correct got me. gentleman, are you saying if it's not code you do not practice it? Remembering code is bare minimum? Are you the same person that runs emt with not ground because "it's code"? As far as the cutting into the wire, remember we are only tightening to what it was originally set to, so it shouldn't cut anymore into the wire that it already did because it shouldn't have loosened at all according to your assumptions. If you tighten a lug with aluminum, it will be under tightened in 6 months to a year. This is something we both teach and practice here. I have never been on a call because someone over maintained aluminum connection, I have been on several that are cause of no maintenance. Never once did I say it was code, kinda like it's not code to use anti shorts with mc cable, but we do or at least you should... again please name a time where you saw an over maintained aluminum termination fail because of that? And I can tell you of plenty that failed because they where never retorqued. Also, I said number 2 is fine but #3 is acceptable? I'm the one saying that it wasn't needed? This was all my suggestion to the original post. I said I would go copper here is why.... if we are talking code, then we should cut that conduit down to an 1 1/4 but nobody is saying anything about that. If you want to have a bare *** minimum conversation let me know and we can.

 

[ErikinMich]

I really appreciate the advice. I planned on using Al but the Cu was basically given to me so I went that way.
I also planned on putting 2 grounding rods at the sub in the barn (I think NEC is greater then 6' away from each other) Tie the grounds into the the ground bus that is isolated from the neutral. Then run that bus with #8 Cu to basement sub ground bus.
Basement sub is grounded but is also isolated so the equipment ground runs back to original panel and is there attached to a ground rod.

 

[Norcal]

Once torqued to factory specs you do not torque them again, just leave them alone, today's aluminum alloy conductors are not the aluminum of the past,

 

[pattenp]

Aluminum connections being retightened as a regular maintenance procedure is not needed nor should be suggested.

http://www.aluminum.org/resources/electrical-faqs-and-handbooks/electrical

Q10) Do aluminum connections need to be periodically tightened to maintain a good electrical connection?

No. Connections on either aluminum or copper should not be retightened after installation following manufacturers’ installation instructions. Connector test performance requirements are based upon no retightening. NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, does not call for retightening aluminum conductors. Connections should only be tightened if there is evidence of a loose connection. Both over-tightening and under-tightening can cause failure of aluminum or copper connections. Unwarranted re-tightening of screw-type connectors can lead to failure of the connection with either aluminum or copper conductors.

 

[ErikinMich]

Next question. I am doing this by pulling a permit and everything is all on the up and up but since I am running the lines, is there a way to use the same lines to to run a generator and feed my main panel ? I would have to put in a switch (interlock or transfer) at the main I know that much, but how would I feed the main (with generator) and run off the sub panel legally ? Is there an easier way to do this ?

 

[pattenp]

No you can't use the same feeder wires to the subpanel to feed back to the house via a generator. You will need to run a separate 4 wire feed back to the interlocked breaker in the house panel and install a power inlet in the pole building.

 

[theoldwizard1]

I have no iea what type of equipment you will have in your barn, but I would do a seriuos load analysis before I would go 100A. IIRC, aluminum is limited to 90A.

 

[mike93lx]

I have no iea what type of equipment you will have in your barn, but I would do a seriuos load analysis before I would go 100A. IIRC, aluminum is limited to 90A.

He already has the wire...

 

[n20junkie]

I have a sub-panel right next to my main panel.

When I needed 4 slots for the garage breaker, Moved a few circuits to the sub-panel to free up space. As a matter of personal preference, I don't like stacking sub-panels unless I need to.