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What size wire for a long run to my barn?
Long runs lose voltage. Too small a wire and motors run hot, lights dim, and the wire wastes power you're paying for.
How this works
Two checks
- Heat: the wire has to carry the breaker's amps without overheating (NEC table 310.16, 75°C column).
- Distance: on a long run, the wire also has to keep the voltage drop under your limit.
Whichever needs the bigger wire wins. On farms, it's usually distance.
Before you trench
- Call 811 a few working days before you dig. In NY and PA, it's the law.
- Use cable rated for direct burial, or run it in conduit, at the right depth.
- A separate barn needs its own disconnect, ground rods and ground wire.
- Keep neutral and ground separate in the barn's panel.
Barns are tough on wiring
Moisture, dust, manure gas and rodents wear wiring out fast.
The electrical code has a whole article (547) just for farm buildings. It covers wet and dusty spots, GFCI, and the equipotential plane where livestock stand.
This is for planning and getting prices. Conduit fill, other wires in the same trench, heat and local rules can all change the answer. Have an electrician check it before you buy wire.