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I would like to add a garage heater (Cadet "The Hot One" - 5000/3333watts - two settings)

I currently do not have any 240v access in my garage.

My main panel is in my basement and my garage is attached so if I measure from my main panel to the interior wall of my garage where the electric would feed from the main panel the run is about 22 feet - The electric heater would be mounted about 20" from the garage ceiling so the receptacle could be above or below so that would put that full run at about 25 feet.

I have a 200 amp service and currently have 9 slots available in my panel.

My understanding is the cadet heater needs a 30amp breaker, NEMA 6-30R outlet and I think I can run it with 10/2 cable.

I would run the line up through the garage wall plate and have the cable behind the drywall and run it into a metal box for the NEMA 6-30R outlet.

I am unclear if the 10/2 is sufficient, I believe it is, and then about grounding the box receptacle box.

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    As a sidenote: what make/model is your panel? (Just want to check that you can get breakers reasonably for it) – ThreePhaseEel Nov 8 '19 at 0:59
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These heaters need what the UL-approved instructions say they need. However this heater is rated for a 20.8A draw.

For heaters, we must provision 125% of that, or 26 amps. That is too much for a 20A circuit, and appropriate for 30A.

10/2 will get the job done for this one task. But it'll do more for your resale if you use 10/3, because that will allow you to fit a dryer or subpanel here in the future. (a subpanel is an easy solution to the old saw + dust collector problem and many other problems you get as you develop your wood or machine shop). You can go ahead and use a NEMA 6-30 receptacle, and just cap off the neutral.

Speaking of over-wiring, there is certainly no harm in using 8/3 or even 6/3 cable, which would allow larger heaters or full development of that subpanel. The ultimate "future expansion" option is to fit 3/4" conduit instead of cable, and simply throw the wires into the pipe that suit your needs at the moment.

  • 10/3 would still be limited to 30A, so not really appropriate for most dryers and as a sub-panel feed, it's still limited to a 30A sub-panel. I agree though that it would be a good idea to use 10/3 however, it's more versatile even if you will not have anything to terminate the Neutral to on a NEMA 6-30R. – JRaef Nov 7 '19 at 19:00
  • @JRaef, I've never seen a dryer that wasn't 30A in the US. Are higher amp dryers common in other parts of the world? – JPhi1618 Nov 8 '19 at 15:00
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Your understanding for wire and breaker size feeding a nema 6-30 receptacle are right. Your length is no where near distance to be concerned about voltage drop requiring larger wire. A metal box must also be connected to the receptacle ground, usually by pigtailing or by wrapping the ground wire around the box ground screw enroute to the receptacle.

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    The NM cable description does not include the ground wire in the count. I know, it's confusing, in the NEC "cable" doesn't include the ground in the count, "cords" include ground in the count. So 10/2 NM is 3 wire cable. 10/3 is a 4 wire cable that includes a white. No neutral connection is needed for a nema 6 configuration, but personally I would be inclined to use 10/3 so if I later wanted to feed something with a nema 5-30 or 14-30 the wires would be present. – NoSparksPlease Nov 7 '19 at 18:44
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    Whats more, OP's current draw is only 20.8amps, so you would compute voltage drop based on 20.8A not 30A. That means you'll be good to 175 feet or so even before 3% which is very conservative... and since heaters couldn't care less about voltage drop, you are certainly good to 300' or more before a bump is called for. – Harper - Reinstate Monica Nov 7 '19 at 18:47
  • I tend to over do things a little, if I was wiring a 30A receptacle circuit I would calculate my voltage drop at at least 80% of circuit capacity. Wow, comment questioning 10/2 vs 10/3 disappeared. – NoSparksPlease Nov 7 '19 at 18:52

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