I'm in the midst of a project, and need power out at my barn. I have a 100' #10 extension cord running lights and a vacuum. I need to run a planer - 3HP motor, 220v.

Ideally, I would be able to do the following:

wire a permanent outdoor 220v 20A (or 30A) outlet
run an extension cord for the 220v machine

Now, can this be done safely? I looked at some charts (length / current / voltage) and if I'm consuming 20A, then a #12 would be sufficient. For 30A #10.

However, I have some concerns since the setup would be:

circuit breaker -> 10' wire -> outlet -> plug -> 105' cable -> socket (in metal box) -> plug -> 5' wire -> planer

Do all of these connections add resistance to the assembly? Is there a difference between solid and stranded #12 when it comes to current carrying capability?

I priced out wire - pretty expensive. I would like to be able to reuse whatever I purchase, and will only have it out for a week. I could move the planer up to the house, but it is very heavy and I would also have to move all of my wood.

 

Would something like this work for the extension? I'd prefer to make my own, but #10 is $1.89/ft so this is priced better.

https://www.amazon.com/dp/B000GAQG7U/

 

A 3HP motor at 240V draws about 9 amps, so you should be OK with a #12 or #10 cord. The problem with voltage drop will be worst when the machine first starts up and when the motor bogs down under load. Either of these could cause a stall and the breaker will trip. I'd suggest to not work the planer too hard -- take light passes. If it seems like the motor is overheating or the thermal breaker pops, you'll need a heavier cord.