I need to connect a 100Amp subpanel at a guest house that I am building in the back of my property. My main panel is 400Amps. I need 120/240V at the subpanel to run a couple of mini split ACs that are on 240V plus your usual lighting and kitchen stuff (cooking and hot water is gas). The distance from the main panel to the subpanel is 260f. I plan to run the wires in conduit, some underground but majority of conduit is along a block fence. I live in the Phoenix, AZ area.
I had planned to use 1/0 aluminum or 3AWG copper wire but it looks like this will not be sufficient to allow for a 3% maximum voltage drop and I should use 3/0 aluminum or 1/0 copper which the online calculator recommends. NEC seems to suggest no more than 5% voltage drop. For 5% allowable voltage drop 1/0 aluminum looks sufficient.
Should I use 1/0 aluminum, or use 2/0 or even 3/0 for the guest house?
Thank you for your feedback.
Best Answer
3% and 5% are there in the form of Fine print notes. These are not enforceable. If your max demand (power used at 1 time) is 100 amps 1/0 will be fine. We would really need to do a load calculation to provide a real value but 270’ 1/0 aluminum is only 4.68% since you have gas cooking and water heater I would guess your demand will be below 60 amps and that would even allow for 2awg at 3.96% so there is no need to go larger than 1/0. : added Aluminum wire is a must for cost here copper would just be nuts for this.