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

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.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.