What size breaker and wire for a barn feeder circuit?

Question

February winds blew down my overhead service to my barn. I would like to replace the 1950's two wire service and update to a safe, sub feed using a complete new underground from a 150 amp house box. The current feed appears to be a branch from the upstairs outlet.(Not good.) The total run will be 150 feet, 50 feet being the underground sub feed.

I have 4 spaces left in the house circuit breaker box that has a 150 amp main breaker. The house has electric water heat, electric oven and range and electric dryer.

Looking for max amperage and wire size to sub feed the barn that would power lights, small power tools, possibly an air compressor and a 110 mig welder. My wife and I would not be using all the electric appliances at the same time. I am semi-retired now, but need to seek advise for this to see if I can do before spring gets here if it will be affordable to our budget. Any help is appreciated.

Answer 1

Based on the activities you are talking about, I would say #4 aluminum.

The reason is 40A will probably suffice for immediate concerns, and you can do that with #8 copper except for the distance. That necessitates a bump to #6 copper, and a side effect of this bump is you get some more headroom, as you can technically drive that circuit as high as 60A.

However, #4 aluminum has the same ampacity as copper at half the price, so why not use it? At these large sizes, the fearmongering about aluminum does not apply, and these wires will be the newer alloy anyway.