I am 350 feet away from my breaker panel in the house to a shop I am planning on using. I need a 30amp 240 volt service for my wood working saws and lights. What size wire do I need to handle the voltage drop. Thanks Jim

Normally a 30 amp load requires 10 awg wire, not sure at that distance though, you may want to go up to 8 awg wire to reduce voltage drop. Someone else will provide input.

I assume you are going to run this to a subpanel in the shop. If this is the case, why not use 6 awg wire and make it a 50 or 60 amp subpanel? This would leave room for expansion in the future.

For every 50' of run you need to up to the next heavier wire. I'd just go with #1and be done with it.

For every 50' of run you need to up to the next heavier wire.Sorry ballen, this is just not true. It may have been an old wives tale back in the day, but we do things a little more accurately now.
You need to do a calculation to be sure.

With a load of 30A @ 240V I get #4cu
With a load of 20A @ 120V I get #3cu.
Both of these are realistic numbers for this installation.
Ironically, the more things running the lower the voltage drop, assuming the load is pretty well balanced. Voltage drop @ 240V is dramatically less than @ 120V.

Personally, I'd go with #4 and a 50A breaker. This is more than safe and reliable for such a feeder.

Why copper? You will have a heart attack when you pay for that much copper and that distance. What would the local utility charge for a pole and drop?

Stan thanks for the info but can you show me how to do this calculation and why a 50 amp when the op says he only needs a 30? Xcbuilder, are you running 240 or 120, I'd do 240 for some shop equipment but I don't know exactly what you have planned.

Stan thanks for the info but can you show me how to do this calculation and why a 50 amp when the op says he only needs a 30? Xcbuilder, are you running 240 or 120, I'd do 240 for some shop equipment but I don't know exactly what you have planned.I don't do the math, I use an online calculator. In the field I have several apps on my phone and iPad.

I would go with a 50A feeder because even though he says he only needs 30A that is a long way to run if he needs more someday. IMO anything less than a 50A sub-feeder is silly.
Also, I like to sometimes check what the drop will be at different amperages and at both 120v and 240v.

Bal the most accurate formula recommend by IEEE is :

Vd= 2*I*L*R/ft

Which is what the on line calculators use. So much easier to use the on line calculators.

While the poster requests copper wire, I would suggest #2 aluminum in a 4 wire URD direct burial cable. If soil conditions are rocky I would sleeve in 3 Inch PVC conduit for extra protection.

Don't we need to know if he is going 120 or 240? The calculator I tried to use requires the voltage

Xcbbuilder states:


I need a 30amp 240 volt service