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I have four infrared heaters that each draw 6.67 amps at 240v.

Each heater has a red, black and green wire: more info (I have SW-24 single lamp model)

I'm in the US and recently had a NEMA 14-50 receptacle installed.

How can I safely connect these four heaters to the receptacle? It is a temporary connection as I only need to do some tests for a few minutes with all heaters on.

My first thought is to wire an extension cable (maybe something like this) to a box with four outlets in parallel?

I'm trying to avoid paying an electrician as it's only a temporary setup and I won't need it after a few minutes of testing.

Any insight is appreciated - thanks!

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This is not legal or safe, but it's safe"er" at minimum cost.

Get a 120mm (4-11/16) junction box and lid, a cable clamp appropriate for that oven cord, 4 cable clamps appropriate for the heater power cables, and three rather large wire nuts, or alternately, 5/6-position lug splices that'll take up to #6. Also 1 foot of bare 10AWG wire, and a #10-32 ground screw (style points for green).

  • The 120mm box has a 10-32 tapped hole in it, put the ground screw in there and attach the pigtail.

  • Knock out holes for all the cable clamps that will make sense when it's mounted to the wall, and fit all the cable clamps, screws out so you can get to 'em.

  • Permanently mount the box on the wall within cord's reach of the 14-50 receptacle. Certainly do not leave it dangling loose. You'll pull cords out that way and give yourself a wallop.

  • Bring the dryer cord into its cable clamp. Tighten it down.

  • Bring each heater cord into a cable clamp. Tighten it down.

  • Use a splice to tie all the following wires: a) the stove cord ground, b) the pigtail from the junction box, and c) 4 ground wires from heater cords. There better be ground wires in those heater cords!

  • Use a splice to tie all the following: a) the heavy black wire in the stove cord, and b) one of the conductors from each heater cable (doesn't matter which).

  • Use a splice to tie all the following: a) the heavy white wire and b) the remaining conductor in each heater cable. Yes, you heard right. White.

  • Put a wire-nut cap on the red wire, and tape it on so it doesn't fall off. Wire-nuts don't like to stay on single wires.

  • Put the cover on the box.

  • Plug in the 14-50 plug. Light this baby up!

If you are getting the expected/advertised heat, then you are wrong about the heaters being 240V. They are 120V. By hooking up this way, we just saved the heaters.

If they're all heating but the heat is 1/4 of what you are expecting, then you passed the test. Unplug the 14-50 cord. Reopen the box, and redo the last 4 steps, but attaching the red wire to the heaters, and capping the white. Now you should get the works.

This isn't legal because these are not permissible uses for flexible cords, and we're abusing the tap rules, and these heaters are not listed to be portable or temporary heaters. The proper way would be a subpanel, 20A breakers feeding 6-20 receptacles, and proper cordage to heaters that are made to be portable.

  • The only legality issue I see with your setup is point 3 you raised -- once you're into a cord-and-plug connected apparatus, the tap rules are no longer a concern, and we're using cordage here to facilitate the interchange of equipment (as this is temporary), so that's not an issue either. This leaves the heaters not being listed for this service as the only issue... – ThreePhaseEel Jun 15 '18 at 7:46
  • Truly appreciate the detail in your answer, especially the 120v pre-test. I look forward to giving this a shot. – MikeBman Jun 15 '18 at 16:19
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If your outlet is properly wired, it should be rated to 40 amperes continuously. Four of the heaters you describe will draw less than 30 amperes, keeping you within a safe range.

A single extension cable rated to 40-50 amperes will handle the load to the end of the cable. Saving the rather substantial expense of four outlets, you might consider to use properly sized wire nuts to join the pigtails from the heaters. As part of this research, I discovered the existence of set-screw wire nuts, something that would be better able to handle multiple wires, but for the size you require, I'm not so certain.

Slightly more expensive would be to use terminal blocks to join the wires providing a more secure mechanical connection.

I think the key item here is "temporary" and that you are not exceeding the capacity of any of the wiring to be used.

  • Where I am lost is the 3 wire connection from the heaters to the 4 prong outlet...how do I connect the red, green and black wires from the heater to the outlet extension? I emailed the manufacturer and they gave a cryptic response: "The single element heater only uses a common and then either the black or red for its hot leg. Not all 3 wires that is with a 120V circuit" – MikeBman Jun 15 '18 at 1:11

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