You really need to compute voltage drop on your actual/expected loads, not breaker trip. I'm pretty bold with allowing voltage drop, Ed's a bit bolder - but if Ed recommends it, it's a good choice. There's nothing wrong with Ed Beal's wire sizes. If it costs more than 1/3 that for all 4 wires, it's the wrong stuff for the job. I want to make sure I am buying the correct wiring for the job. I'm getting that a lot from A/C contractors these days lol.Īlso, the wiring seems to be about $7.75.ft at Lowes. That seems like the 'I don't wanna do it' price or 'I got more customers than time so I'll charge markups on everything' price. Third, that size completely ignores voltage drop which will be considerable on a 300' cable run. If it is a legal domicile, #2Al (normally 90A) will suffice. If it's not a legal domicile, minimum size for 100A is #3Cu or #1Al. It doesn't apply to everything with 'house' at the end of the name, only things which are legal and proper domiciles (ADUs) equipped and permitted for people to actually live there - bedroom, competent kitchen with range, etc.

Second, #4 COPPER is only good to 85A not 100A. (30A copper wire is about the same price as 90A aluminum wire). Once you get to about 30A it's time to investigate whether aluminum is a better choice. The electrician told me I need #4 wires from the main to the sub.įirst, using COPPER for a heavy long feeder isn't even stupid. The main panel is a 200 amp panel about 300 feet away from the sub panel.

100 amp panel