This article series gives photos and tables of electrical service entry cable sizes, electrical branch circuit wire sizes, bell wire, telephone wire, thermostat wire, and ampacity or fuse/circuit breaker ratings. We include links to wire size and voltage drop calculators. We have no relationship with advertisers, products, or services discussed at this website.Įlectrical service entry wire sizes are calculated for long wire runs in which the wire size must be increased to avoid an un-wanted voltage drop. 120V loads all on one leg.InspectAPedia tolerates no conflicts of interest. I don't believe a shop gets the "special derate for a dwelling service" that might allow smaller wiring (for both) but if I'm wrong one of the normal electricians will be along to correct that.Īs a feeder, your neutral wire size can possibly be reduced, but only if a calculation supports that (it has to be at least as large as the required grounding conductor, and it has to be large enough to carry the maximum calculated unbalanced load (i.e. Your grounding wire needs to be 2 AWG insulated aluminum based on the 250 kcmil feeder. Since the maximum load that can be planned on 200A service is 160A, and 160A has a voltage drop of well under 4% at 250 feet on 250 kcmil aluminum, we can skip extracting the details of your load to do a formal load calculation unless you are in Canada. 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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