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microtcpip 03-27-2006 05:15 PM

Wiring gage questions
Wiring gage questions

We are currently digging a trench to have an exterior wire go from the house to a back barn. The distance is about 120 feet and the electric in the barn is going to be use for lighting. Could you please tell me the correct gage and wire type for this project?

Your help is greatly appreciated

RobertWilber 03-27-2006 05:41 PM

Just Lighting? How much lighting?
Never going to need a drill out there?
And you don't weld or anything?
And won't put a tiny little fridge out there for when you are working on the brakes?

microtcpip 03-27-2006 05:44 PM

wiring gage questions
Is a horse stable, so just horses back there… Perhaps a dozen light bulls all together...

Good point... I used the word barn!:)

RobertWilber 03-27-2006 06:17 PM

Robert Wilber
Licensed Philadelphia Electrician
Philadelphia License # 3516 - 16765
I would humbly suggest that you pull a circuit out there for a receptacle too.
If you have 12 x 100 watt lamps, then you will be pulling 10 amps on the line.
Run a separate circuit for a receptacle as well, and put in a GFI.

120 feet is a 240 foot roundtrip.
the formula for wire size is a corollary of the voltage drop formula.

Voltage drop =KIL/CSA where K is conductance, I is current, L is circuit length and CSA is cross sectional area in circular mils.

so... CSA= KIL/V drop

CSA= 11 [K factor of copper] x I [say 12 amps] x 240 feet / 3 volts
CSA= 11*12*240/3=10,560 circular mils
10 gauge is 10,380 circular mils. Sounds like a good fit.
So, run 240 out on a 10/3 with ground type UF cable out to the stable and put in a 2 circuit loadcenter.
Make sure to isolate the neutral from the ground at this panel.
According to NEC 250.32 it is not required to have a ground rod at the stable. I think having one might create problem ground currents that could interfere with the horses, but get advice from your local inspector and the authority having jurisdiction.
I haven't done this myself, so I haven't checked my opinion on this with any "Authority Having Jurisdiction"
This is my interpretation of what I have read in the 2005 NEC
This information is provided for the use of parties as they see fit!
I am not responsible for the application of this information by any party, including those lacking sufficient skill or knowledge to perform these steps safely and any hazard created is the SOLE responsibility of the user.

microtcpip 03-27-2006 06:23 PM

Thank you soooo much!!!
I really appreciate that you took your time to explain why and how you calculated that!!!

Pretty neat and tidy, Thank you so very much


RobertWilber 03-27-2006 08:37 PM


jbfan 03-27-2006 09:12 PM

Make sure you protect the wiring. I've seen horses chew anything and everything.

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