I am planning to install a NEMA 14-50 outlet in my garage on a 40A breaker (Romex 8/3 cable from breaker to outlet) for use with an electric car charger. The charger will charge my wife's car in the wee hours overnight.

The charger also has the option of coming with a NEMA 6-50 plug rather than the 14-50, if that's a better option.

Sometimes in the winter, I like to work in the garage. So, I got a plug-in heater that has a NEMA #6-30 plug and requires a 30A circuit.

I'd like to be able to unplug the charger and plug in the heater. Since the heater draws less power than the charger, as long as the circuit is sized for the charger I think this should be OK. Assuming so, here are what I see as my options:

  1. Chop the 6-30 plug off the heater and replace with a 14-50 (or 6-50) plug.

  2. Get an adapter from 6-30 to 14-50 (or 6-50).

Would appreciate any thoughts on this: Is it feasible? Are there better options (aside from running a separate circuit for the heater)? Is there any advantage to getting the charger with a 6-50 rather than a 14-50? Is 8/3 Romex sufficient?



  • What is the rating of the charger? code considers chargers to be a continuous load so the wire size should be 125% #8 is good for 50 amps. Next what is the heater rated at? To be code compliant the breaker cannot be above 150% of the appliance (heater). If the heater is rated at 24 amps like mine a 40 amp breaker is two large. – Ed Beal Oct 3 '16 at 19:45
  • @EdBeal Does that change if a power tool (like a table saw) is plugged in instead of a heater? I can make a new question if needed... – mmathis Oct 3 '16 at 20:01
  • This is slightly different question table 210.21.b.3 lists permissible loads for circuit ratings may be helpful here. 15 amp circuit not over 15 amp receptacle. 20 amp circuit 15 or 20 amp receptacle (more than 1 15 amp outlet required). 30 amp circuit 30 amp receptacle. 40 amp circuit 40 or 50 amp receptacle. 50 amp circuit 50 amp receptacle. So if you have the correct cord cap and the single device is not over 80% of the branch circuit rating (210.23.1). The 150% is for non motor appliances (422.11). With motor appliance code allows for larger OCPD so the breaker won trip on start up. – Ed Beal Oct 3 '16 at 20:35
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    Ed: Thank you for the feedback. Charger is 40A, so maybe I need a 50A breaker. But from what you said, #8 should still be fine. Not sure of heater's rating--will have to look that up. But I'm curious as to the reasoning behind the breaker not being more than 150% of the appliance. Generally, I'd think that drawing well below the capacity of the circuit wouldn't be a problem. But obviously I'm missing something here. – An Ex Parrot Oct 3 '16 at 21:23
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    Car is a Chevy Volt. Charger only requires 40A; I believe it has the 50A because those are common for RV hookups. – An Ex Parrot Oct 4 '16 at 0:48
  1. Chop the 6-30 plug off the heater and replace with a 14-50 (or 6-50) plug.

14-50 right angle plug

That's going to be the cheapest option. Not bad if you know you're never going to move that heater around. These plugs are readily available at home improvement stores.

  1. Get an adapter from 6-30 to 14-50 (or 6-50).

Flexible and reusable parts option. Modeately more expensive, and those are not very common adapters to find. You will probably have to build one from parts. I'd buy a 14-50 stove code, and outdoor rated outlet box to put the 6-30 in.

Better yet, get an outletbox that's twice as large, and put a 6-30 and 14-50 on it, so you can keep both plugged in at all times. Just keep in mind if you use both at once you're likely to trip the breaker just as if you turn on too many appliances in a kitchen at once.

Are there better options (aside from running a separate circuit for the heater)?

You could run a subpanel.

If I was you, I'd run a 100A service from the main panel to a subpanel in the garage. Garages are a great place for a subpanel. If you decide you want to run both the charger and heater at once, you can, and you can add capacity for a compressor, or power tools later on easily, too.

I'd recommend if you add a subpanel in your garage to include a pair of 20A outlets nippled to the sides of it just to have it available.

You could then hardwire the charger and heater, and save cost and eliminate visual clutter of the outlets and plugs.

Is there any advantage to getting the charger with a 6-50 rather than a 14-50?

I would not expect there to be much difference, but you didn't say what chargers you're referring to. I would buy whatever's cheapest, and I'd probably hardwire it to the subpanel to save on connector cost and risk of connectors breaking.

Is 8/3 Romex sufficient?

I'm going to refer you to an NEC ampacity table so you can make that decision for yourself, but I wouldn't use 8AWG for 50Amps

Assuming you're using Copper and its going to be instaled in a wall, I'd use 6AWG.

Or run the subpanel with 1/0 (one ought) aluminum or 1AWG copper, and then I'd be comfortable using 8 AWG to a charger directly adjacent to the subpane.

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