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I have 2 30 amp breakers on a circuit that only has a 30 amp receptacle for my dryer. Can I tie into this circuit to hard wire a 30 amp 7500 watt garage heater?

  • Someone else will speak to the code issue. But from a practical standpoint, the heater will use the full power of the circuit (actually more as 30a x 240v is only 7200w) so if you turn on the dryer when the heat is already on you'll overload and trip the breaker. – manassehkatz-Moving 2 Codidact Dec 26 '18 at 2:44
  • Is there a reason you want to tap into this circuit instead of running a new one from your panel? – ThreePhaseEel Dec 26 '18 at 3:08
  • FWIW, 7.5kW may be overkill for your garage, depending on how large & well insulated it is and where in the world you are. I have a 2kW heater in my double garage with reasonably well insulated walls but only a 'normal' fiberglass roll-up door and I'm in northern GA. – brhans Dec 26 '18 at 15:04
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Your heater is 7500W, which is 31.25 amps, and because it's a heater, it must be derated to 125% or 9375W or 38.8 amps.

That is too much for a 30A wire and breaker, but is "just right" for 40A wire and breaker. That is designed that way on purpose.

So you need to use #8 cable, e.g. 8/2 Romex. And a 40A breaker. The 30A/10AWG wires are not suitable for this heater.

If you want a heater able to exploit the #10 cable and 30A breaker, pick one whose output is 5300-5500 watts (22-23 amps). That, multiplied by 125%, will fall just under 30A.

If you are connecting it via cord-and-plug, Code requires you use a 50A receptacle. You can either use a NEMA 6-50, which does not include neutral, or a NEMA 14-50 receptacle (but then you need to run 8/3 cable).

If you also want to plug in actual 50A loads, such as an RV or electric vehicle charger, then run 6/3 cable to a NEMA 14-50 and use a 50A breaker.

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