Electrical – Wiring 240V Two-Element Outdoor Heaters

electricalheatingnecswitchwiring

I installed an electric heater over my covered deck last year. My intention was to design and install a system that complied with NEC and would pass an inspection. I initially installed a single Infratech WD-3024 heater, and recently added a second.

My question: The below drawing shows a 3-wire method for wiring a 240V heater, which switches one 120V leg and not the other. Is this not compliant with NEC 424.19?

https://www.infratech-usa.com/wp-content/uploads/DUPLEXSTACK-SWITCH-WIRING-FINAL-0521.pdf

Background info:

My question is related to this one:
Wiring Infrared Patio Heating Systems

I mounted a subpanel on the exterior wall of the house and made the run to the main house panel with big cable (4/3 NM-B). Power at the main box is switched with a 50-amp breaker. Each heater can draw 12.5 amps with both elements on. Since it's a continuous load, I derated to get 16.25 amps. There are 2 20-amp double pole GFCI breakers in the sub panel, one for each heater. Wiring runs from the subpanel to a switch box, with two duplex switches. From the switch box, 7 wires (four black, two red, one green) run out to the two heaters.

I followed the 3-wire drawing provided by Infratech above, for each heater

(note that they previously provided both a 3-wire and a 5-wire drawing, which I can't seem to find on their site anymore, but is here: https://www.infratech-usa.com/wp-content/uploads/2014/01/infratech_duplex_stack_switches_dwg.pdf)

Infratech also offers some simple on/off duplex controls:
https://www.infratech-usa.com/wp-content/uploads/in_controlssheets_2015-duplexstack.pdf

Due to the price and availability of the Infratech models, I used a different switch. Each heater is controlled by a Leviton 5334 duplex switch, one throw for each element. As in the drawing, only one leg of the 240V circuit (the black one) is switched, the second leg (red) goes straight to the heater.

While doing the second install I recognized that this scheme leaves one leg of the 240v supplied at all times, which gave me a bad feeling. Looking with fresh eyes at the NEC, 424.19 seems to indicate that this is not a valid installation.

If it's not, what changes must I make?

  • I assume there is no such thing as a double pole duplex switch? I
    can't find one and it seems that would pack a lot of wires into a
    small space. I can imagine a 4-gang box with 4 double-pole switches,
    it's disappointingly ungainly.
  • Will I have to run independent red wires to the heaters as well? It
    seems like this must be necessary. I ran 3/4" Sch 40 pvc conduit so I
    should have space. Just disappointing to have to pull the wire again.

Bonus: So what are those switches Infratech is selling?

Best Answer

Get a couple of HOMELEC2PALAs and fit those to the heater breakers in the panel

Under NEC 424.19(B)(2), for a heater without its own (supplementary) overcurrent protection and no motors upward of ⅛ hp in it, you can use the branch-circuit disconnect as the required all-pole disconnecting means provided it's either in sight of the heater or lockable in the OFF position:

(B) Heating Equipment Without Supplementary Overcurrent Protection.

(1) Without Motor or with Motor Not over ⅛ Horsepower. For fixed electric space-heating equipment without a motor rated over ⅛ hp, the branch-circuit switch or circuit breaker shall be permitted to serve as the disconnecting means where the switch or circuit breaker is within sight from the heater or is lockable in accordance with 110.25.

So, the simplest fix for this problem is to fit the heater breakers (HOM220GFICs) with matching HOMELEC2PALA lockoff devices, and get a couple of thin-shackle padlocks (they don't have to be fancy) that you can keep with your panel so that you (or an electrician) can lock out the heater when working on it. This way, no knave can turn the heater back on whilst you are working on it, which is what the Code is trying to prevent.

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