![]() The load calculation helps to determine if the wires should be increased in size at long distance, or if that's not needed. The breaker sizing sets a minimum size of the wiring for any distance, no matter how short. Wire sizing ALSO depends (secondly) on the load calculation (which is not breaker size) for the loads to be supplied in the shop building. With (typical, likely) 75 ☌ rated terminals at both ends this sets a minimum size of 250 kcmils for aluminum wire with an insulation rating of 75 ☌ or more. You've now commented that this will be 200A. Size of wires, grounding wire, conduit for wires all depends (firstly) on what the breaker supplying the power will be rated at. ![]() You would use any suitable wet-rated wire, which might be THWN, THWN-2, XHW, XHHW, RHW (and there are others beyond those.) When you bump the conductors you must bump the ground too in proportion, to #1 Al. If you are going to be pushing the limits of the 200A service, going up a size to 300 kcmil will take care of voltage drop (2.88% 160A). Still, at 160A (the maximum you can plan to use on a 200A feeder), voltage drop will be 3.9%.Ĥ/0 or 250 kcmil wire requires a #2 aluminum ground. It lets you call it an honest 200A feeder, and voltage drop will be less of an issue. You are really better off using 250 kcmil. Which will start to be an issue at this distance. Technically legal, but it ignores voltage drop. You would use 180A wire (#4/0 aluminum) but since they don't make 180A breakers, you'd round up to the next available size - 200A. You could declare the feeder and garage load to be 180A. ![]() Anyway, it operates off the service size not the feeder size, so if your service is 400A, it is saying no feeder needs to be larger than 600 kcmil. Ecnerwal is correct that the 310.15(B)(7) "favorable derate" does not help you. ![]()
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