Wiring gage questions
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
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