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I am installing a 4000W infrared heater in our new patio. The supply for this heater is a single phase 240V connection (rated at 16amps, so I'll use a 20amp breaker). I would like advice on two things.

Thing #1. I need the heater to run on a countdown timer, and I don't like the ugly timers that are available for 240V circuits. The switch will be in our new dining room, which will have Decora switches and outlets. So I would like to use a preset 120V fan timer that fits with the look, something like the LTB02-1LZ. Of course that is a 120V timer, so if I use that, I am wondering what relay or contactor I could use here, that has a 120V coil to switch on a 240V/20A circuit.

Thing #2. I will be mounting this on a wall, and the unit has brackets that are about 10" long to stand it off from the wall. The power supply wiring will come out of the wall, run behind one of the two brackets, and then go into the junction box on the heater. The installation instructions say:

"Junction box has a 0.86” (22mm) to a standard 1/2" weather tight conduit fittings. Install cord grip with minimum rating of IPX4 to maintain the water ingress protection rating of the heater. Cord grip must have minimum temperature rating of 90°C (194°F). Failure to install correctly will avoid the manufacturer’s warranty....For supply connections, use suitable power supply wire at least 90 ̊C (194 ̊F)."

So, specifically what does all this mean? What do I need to use in order to make the connection from the wall to the heater, and pass inspection for an exterior location? Conduit? NM-B? THHN?

2 Answers 2

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Per NEC 424.3(B), heaters get a 125% derate when considering wires, controls and breakers. Thus your 4000W heater derates to 5000W, or 20.83 amps.

As such, it needs 10 AWG wire and a 25A breaker. The breaker will need a locking kit per 424.19.

Further, the Leviton LTB02-1LZ timer lacks the capacity to switch the heater directly, and is not allowed on a 25A circuit. It does, however, have the capacity to switch a relay.

Thus a relay such as a RiB or Aube could be used to ultimately control the heater. If the heater has a 24 volt contactor onboard, the 120V timer could power a small 120V to 24V transformer located anywhere convenient.

"Junction box has a 0.86” (22mm) to a standard 1/2" weather tight conduit fittings

That is also called a "standard 1/2 inch knockout". You need to get a watertight wire whip or short liquidtight flex conduit to go from wall to heater. 90 degrees C is a standard rating for most conduit fittings and wires, such as THWN-2.

NM-B isn't allowed outdoors and UF-B is only 60°C thermal.

I would fit a junction box on the outside wall. However it might also be possible to have a hard pipe come through the wall, have a coupler, then go to flex. You need a junction box somewhere to transition from #10 NM to #10 THWN-2.

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  • confusing as hell. So for 4000 Watt heater the OP needs 5000 watt controller, how would a mortal person know that.
    – Traveler
    Commented Jan 10, 2023 at 4:53
  • Why would the OEM label they product as 4000 W when as you say it is actually 5000 W
    – Traveler
    Commented Jan 10, 2023 at 5:11
  • @Ruskes It's 4000W actual. Truth in advertising. You need to provision 125% power to it, it's the same derate everything gets. You call it the 80% rule but it's the same thing. So you need a 5000W circuit. I didn't downvote you, someone else did. Commented Jan 10, 2023 at 7:17
  • as I said, confusing for us mortal people. The label says 4000 W Heater. Normally I would shop for 4000 W controller. You say that is not correct.
    – Traveler
    Commented Jan 11, 2023 at 0:25
  • @Ruskes you may be confusing yourself on the controller. I didn't mean to say the controller needed to be 5000W, the controller will have the 125% derate accounted for in its instructions, which you need to follow per 110.3(B). I mentioned "controller too small" to OP because that controller is. Also it's a fan controller and its instructions may not allow heater. Commented Jan 12, 2023 at 7:12
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Since you have more that one question, and that is no/no here, lets answer one at the time

Thing #1

You can not use your idea using the LTB02-1LZ

It only works with 120 Volt and up to 1800 W.

Since you are looking for something decorative, here is a product that suits your needs.

"Stelpro 4000W Dimmer and Timer Control for Infrared Radiant Heaters, 240V "

timer

You can find it at following place or other places.

Stelpro

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  • 1
    I might be missing something, but this seems like a good answer to the question.
    – crip659
    Commented Jan 10, 2023 at 20:06
  • @crip659 one would say so, but than there are some
    – Traveler
    Commented Jan 11, 2023 at 0:04

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