i want to install a 4800 watt construction heater in my garage that is already wired with a 60 amp subpanel. It has lots of room for extra breakers in the sub panel so i plan to install a 30 amp breaker (the heater specs say it is 21 amps, so the 30 amp breaker appears correct)..

The heater will be plugged in 42 feet from the subpanel so i estimate it will take about 50 feet of wire.


  • A 30A dryer circuit, for example, would take #10 wire. I don't believe that a 50' run results in enough voltage drop to warrant upsizing. Disclaimer: not an electrician or an NEC expert – isherwood Aug 11 '16 at 20:54

10 AWG wire.

THWN type if in conduit.

NM type if using plastic sheathed multiconductor cable. 10 AWG is typically orange. 10/3 if it needs neutral, otherwise 10/2 and re-mark the white wire as a "hot" by wrapping it with black tape.

Many 240V heaters do not need a neutral. But if you include neutral, you may thank yourself later, because it'll give you the most versatility in terms of other things you might plug in there in the future.

You can also look at the plug for your heater and see what it requires. Even if it doesn't require a neutral, you are perfectly welcome to run a neutral, and simply cap it off in the electrical box for future use.

You must choose. You are not allowed to put 2 receptacles on a 30A supply cable in this type of installation. The NEMA 10-30 is bad news and should be avoided, anything that requires it, you should replace it with 14-30.
enter image description here

| improve this answer | |
  • thanks for your comment. how do i tell if it needs a neutral or not? I haven't bought the heater yet, but they are about $125 at home depot and they are called construction heaters and they have the same plug end as a welder. (220) . So it is 10 AWG wire 10-2 or 10-3 any colour but white. – guy Aug 12 '16 at 3:21
  • Look at the welder plug or the plug on the heaters. If it's NEMA 14( has 4 pins), you need a neutral. If it's NEMA 6, you don't. If it's NEMA 10, get rid of it., it's obsolete, dangerous and illegal for new work. I'll edit my answer later with photos of the various connectors. – Harper - Reinstate Monica Aug 12 '16 at 16:30

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.