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I want to install a 220 heater in my garage. The heater draws 31 amps. The run will be 26 feet. Would I use a 40 amp breaker and and N0. 10 wire?

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You need 8AWG and a 40A breaker for this equipment

You'll need to run 8AWG for this circuit -- NEC 424.3(B) requires the 125% continuous load modifier to be applied to the nameplate rating of the heater, meaning you need to size the wire and breaker for 38.75A of load.

Two hots and a ground should be fine

Most electric heating equipment runs solely off 240VAC, which means that you only need to provide it with two hots and a ground, unless the equipment installation instructions specify a neutral is required as well. In that case, you'll need to use 8/3 cable for this; otherwise, 8/2 is OK here, given that nothing else can be attached to this circuit anyway.

  • Personally, for the relatively little extra money it would cost, I'd put in 8/3 anyway just in case the heater is swapped out for something different in the future that does require the neutral. – stevieb Oct 17 '18 at 15:21
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10 awg wire is only rated for 30 amps. I think your 31 amps is the maximum that the device will draw, but I could be mistaken. For a 40 amp circuit, you'll need a minimum of 8 awg wire.

Not sure of your location or of the codes in your area, but in Tennessee, you'll need 4 conductor wire. 2 hot wires, 1 common/neutral, and a ground.

  • Is there a local amendment where you're at that requires a neutral to be pulled to a piece of utilization equipment that doesn't need it? – ThreePhaseEel Oct 16 '18 at 23:00
  • You don't need a neutral unless the heater requires it generally. – Harper - Reinstate Monica Oct 16 '18 at 23:25
  • Sorry for the misinformation. While writing this I was have a conversation with someone else about a stove circuit... Common/neutral isn't required. I however, would run a neutral for possible future use. – BillWeckel Oct 19 '18 at 14:03

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