20 amp service to an outbuilding 250 to 300 ft.

JStofik

20 amp service to an outbuilding 250 to 300 ft.
What size wire do I need?
Is LED lighting safe to use in a barn environment- ie dust and hay?

brgmgb

The wire size calculator says minimum of #3 for 120v.

k_buz

That's what it says, but there is no code requiring voltage drop sizing. I would run #8's to the outbuilding, then switch down to #12 for the wiring inside.

mpoulton

What is the actual load? For that long of a run, you might be better off running #10 or #12 wire at 240V, with a transformer at the far end for 120V. This save copper, at the expense of using a transformer. The exact nature of the load will be important.

And yes, LEDs are fine in a barn environment.

Yoyizit

A 7v drop at 20A. Maybe use a buck-boost transformer in the boost mode at the destination end. That way the xformer only has to handle 140 VA.

Hay ignites at 170C and LEDs run much cooler than this.

mpoulton

Have to be very careful with this. It's a great solution if the load is lighting only and always constant. But if there is any variation in the load this will result in unacceptably high voltage when the load is minimal.

k_buz

I wouldn't think twice about a 7V voltage drop.

dmxtothemax

To minimise losses on the long feed line,
I would use a bigger gauge of wire.
I would use 6# for the main feeder line.
Then around the building you can use smaller 8#.

JStofik

Thanks to all for responses.
The building will have 3 or 4 lights and 3 small horse bucket heaters and 1 utility receptacle

Based on your feedback, I think I will go with #8 copper 120v and #12 after entrance to feeder box.

kevinp22

for that distance I would do a little future proofing and run #6

Yoyizit

Yes, you have to get a xformer with good regulation such that at zero load you're maybe +10% above nominal value and at 20A you're at -10%.

PoCo's xformer is right outside my house so a 20A load drops the 240V by 0.4V measured at the panel so that's probably the best regulation you can reasonably expect.

CFLs or LED lighting may not be nearly as sensitive to overvoltage as incands.

curiousB

Why not use 240V heaters? They are likely the dominant current draw in your load. By going 240 you'll cut current in half and can probably go with 15A branch circuit. You'd have to run three conductors plus ground so that offsets some of the benefit of the smaller gauge wire but still probably better.