# What size wire to use for long run?



## bhry (Sep 23, 2010)

I want to run electricity out to my pole barn from my house. It is about 350 feet away. I want to have a small breaker box in the pole barn, with two 20 amp circuits (one for lights and the other for outlets). 

The house has a 200 amp box and lots of extra breakers, so I'm not concerned about that. 

I am going to rent a trenching machine and put the wire in PVC conduit.

I need to get the trench dug and run the wire soon because of my work schedule in the fall. The actual part of hooking up the wiring, I might have someone else do that. But I need to do the trench now, so I need to know what size wire to run. 

Thanks for any advice.


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## Techy (Mar 16, 2011)

#4 Copper or #3 AL would do well


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## gregzoll (Dec 25, 2006)

You can run both off of a single 10/2 20 amp circuit, with a junction box to feed the lights and receptacles off of, if you do not plan on running any heavy duty equipment. Otherwise, wire like Techy said for a 100 amp service out there for 240 service, in case you want to weld, use power tools, etc.


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## bhry (Sep 23, 2010)

Thanks for the wire sizes. 

I have a garage where I run all my power tools, so I don't need that many amps for the pole barn. And I don't want to spend too much money on the wire, since it is pretty long. 

The pole barn has 5 light bulbs in it now and I might add a few more. I want to run an electric chain saw in the building, and those can use quite around 13 amps. And I might have a radio or something. So I think it would be best to have two 20 amp circuits. I also want it to have it's own breaker box so I don't have to go all the way up to the house if I trip a breaker.


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## gregzoll (Dec 25, 2006)

Sorry, but you will need min. #3 (20amp circuit, 120 volts) for the run. You could do #10, but that length, you would end up with a really bad drop, and would notice when flipping on the lights, or running an compressor.

http://www.elec-toolbox.com/calculators/voltdrop.htm


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## bhry (Sep 23, 2010)

Does the #3 go by another name? I am looking on the Lowe's website where they have 14/3, 12/3 etc cable sizes. Assuming the #3 means 3 gauge. So do I need 3/3 wire? I don't see anywhere that sells that....


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## AandPDan (Mar 27, 2011)

The big box stores most likely won't have #3. You could try an electrical supply house or use #2.

Since you said you were running it in conduit, you'd want #3 THWN conductors.


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## bhry (Sep 23, 2010)

This is starting to sound expensive. Would it be possible to step it up to 240 volts and then go back to 120 volts in the barn, and use a smaller wire?


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## gregzoll (Dec 25, 2006)

Actually you have to have it cut off of the big spool. It is a bulk purchase item. 350 is pretty heavy, better to purchase from local electric whole seller, due to they will spool it for the OP.

bhry, does not matter if 3 wires or 4 wires, it is still expensive for that length of run, and the type of wire. Check with local electricians.


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## kbsparky (Sep 11, 2008)

Sheesh! All this overkill about a perceived voltage drop!

Figured at full load (20 Amps) with little or no drop, you MIGHT have to use such oversized wires, but it's really not cost effective on such an application.

I have run temp circuits using #10 at those distances, and really did not have significant problems with the final voltage at the far end. Sure, some voltage drop was present, but even my shop vac ran fine. WE built an entire steel building using corded drills and saws on those temp circuits.


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## gregzoll (Dec 25, 2006)

That was what I was thinking also Sparky. But the calculator throws you. I wonder if he could use #8 instead of #10, to give the edge of possibly going 240.


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## Code05 (May 24, 2009)

gregzoll said:


> That was what I was thinking also Sparky. But the calculator throws you. I wonder if he could use #8 instead of #10, to give the edge of possibly going 240.


Using a #10 at 240v 20 amps I get 223v at the barn under load.

#8 is 230v


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## Code05 (May 24, 2009)

At the bottom of this page is a better calculator.

http://www.mikeholt.com/freestuff.php?id=freegeneral


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## gregzoll (Dec 25, 2006)

I like that one even better Derek.


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## vtboy51 (Apr 1, 2009)

I'm doing almost the same thing, going about 350' to a sugar house, using #2-2-2-4 alum. direct buriel wire from Home depot, about $1.40 per foot.


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## Code05 (May 24, 2009)

vtboy51 said:


> I'm doing almost the same thing, going about 350' to a sugar house, using #2-2-2-4 alum. direct buriel wire from Home depot, about $1.40 per foot.


what size beaker? what panel type? what are you using for electrodes?


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## kbsparky (Sep 11, 2008)

Code05 said:


> Using a #10 at 240v 20 amps I get 223v at the barn under load.
> 
> #8 is 230v


Chances are he will _never_ approach full load on this circuit. Why not re-calculate for something more realistic, like 5 Amps?


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## Code05 (May 24, 2009)

kbsparky said:


> Chances are he will _never_ approach full load on this circuit. Why not re-calculate for something more realistic, like 5 Amps?


I was validating your answer, not arguing against it. At full load the drop is still acceptable, so a realistic load will be less.


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## vtboy51 (Apr 1, 2009)

Code05 said:


> what size beaker? what panel type? what are you using for electrodes?


Not sure what box I'm going to buy, just what ever small one home depot has. I will be putting in a 100 breaker on both ends.


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## Code05 (May 24, 2009)

vtboy51 said:


> I'm doing almost the same thing, going about 350' to a sugar house, using #2-2-2-4 alum. direct buriel wire from Home depot, about $1.40 per foot.





vtboy51 said:


> Not sure what box I'm going to buy, just what ever small one home depot has. I will be putting in a 100 breaker on both ends.



Nope. Ain't legal. Supply breaker cannot be 100 amps or you need bigger wire.


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## vtboy51 (Apr 1, 2009)

Code05 said:


> Nope. Ain't legal. Supply breaker cannot be 100 amps or you need bigger wire.


Maybe I'm reading the table below wrong, #2 Alum, either a 90amp or 100amp, depending on temp and type of wire. What type is direct buriel? Worst case use the 90amp breaker.


Wire Size and Amp Ratings​ http://www.wiringhelp.com/electrical/electrical-safety/wire-type-and-sizing-considerations.html​


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## Code05 (May 24, 2009)

vtboy51 said:


> Maybe I'm reading the table below wrong, #2 Alum, either a 90amp or 100amp, depending on temp and type of wire. What type is direct buriel? Worst case use the 90amp breaker.
> 
> 
> Wire Size and Amp Ratings​ http://www.wiringhelp.com/electrical/electrical-safety/wire-type-and-sizing-considerations.html​


Direct burial is USE. However USE is limited to a final ampacity in the 60C of T310.16 which is 75 amps.


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