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I am getting two Wexstar 550W infrared heating panels that I will install both on the ceiling. They can just be plugged into a regular outlet. However, per FAQ they can also be hardwired and this is what I want to do with a wall switch to turn them on/off.

I have three circuits closeby where I could wire them into:

  1. A 15A circuit that is only used for lighting. It connects to the lights of four rooms (a total of 11 light fixtures when I count each recessed light and fixture individually). If I turn every single light on, the load is 268W.
  2. A 20A circuit that is used for the stove hood and wires to 5 outlets. The stove hood has a total load of 250W (if I turn on everything to max). Note: This is not a kitchen circuit (there are two separate 20A circuits for that). The five outlets are elsewhere (outside of the kitchen).
  3. A 15A circuit that connects to lighting for 4 rooms and two outlets. The total load when all lights are turned on (and nothing connected on the outlets) is 70W. However, one of the lights is for the basement where I plan to install very bright LED lights, so this may increase. Also, in the one outlet the TV is permanently connected. And the other outlet is next to the dining table where an induction stove or raclette could be connected occacionally.

Both heating panels will be a total load of 1100W. The total load of the first circuit would be ~1400W from an allowance of 15x120=1800W. The total load for the second circuit will be 1350W plus whatever is plugged into the outlets, from an allowance of 20x120=2400W. The total load of the second circuit would be ~1200W but likely ~1400W if I account for the basement lights. And if I were to use the raclette and everything is turned on at the same time, the breaker would trip for sure.

In my opinion I could wire them to all of the three circuits.

Which circuit should I best use and why?

Ideally I would use a dedicated circuit but running a new circuit is really hard and would like to avoid if possible.

PS: Location California, USA.

1 Answer 1

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TL;DR Only # 1 is legal.

The first 15A circuit should be OK. The number to use is actually 12A/1,440W (often referred to as 1500W based on 125V). That's because lighting and these panels are continuous use devices - you might leave them on for hours at a time. Continuous use gets an 80% derate (or 125% multiplier, depending on your point of view). On a 15A circuit that means you can use 12A, not 15A. But 1100W + 268W = 1,368W, leaving a margin of 72W for a few more lights or power used by smart switches, etc.

However, you can't have general use receptacles on a circuit with > 50% hardwired load. Even without the 80% derate, that rules out circuit # 3 (1800W x 0.5 = 900W, which is less than 1100W). The 20A gets closer, but 1100W + 250W = 1350W, which is more than 1/2 of 2400W, and that's also without the 80% derate, which would apply to the heating panels even if it doesn't apply to the hood.

But wait! Why should it matter. If I have the heating panels running and plug in too much other stuff, it will just trip the breaker, right?

Not necessarily. Using the 20A circuit (but there are similar situations with a 15A circuit) and considering breaker trip curves, it is easy to end up in a situation that is enough over the limit to cause problems while not tripping the breaker. For example, if you run the 1100W of heating panels plus a standard 1500W space heater, that is 2600W total. The circuit can only handle 2400W, and that is ignoring the continuous use derate. But that is within 10% of the rated size of the circuit, so the breaker may take a very long time to trip. That's a good reason for both the "50% hardwired rule" (significantly decreases the chances of hardwired devices + regular plug-in loads exceeding the circuit capacity) and the 80% derate (which applies to continuous loads - going 10% over for 10 minutes will not normally be a problem, going 10% over for 10 hours is more likely to be a problem, though by then the breaker will hopefully have tripped).

The rules are not absolutely perfect. But followed properly they take care of a lot of edge cases that would otherwise cause problems.

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  • Thanks. I edited my question, the 20A circuit is NOT a kitchen circuit.
    – divB
    Nov 30, 2023 at 4:21
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    Thanks for the explanations. While I will follow the the rules, it's really frustrating that if instead I would add a new outlet and just plug the panels in permanently, I would not have any issues and everything would be "legal". Although all numbers are 100% identical.
    – divB
    Nov 30, 2023 at 4:33
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    As far as I can tell, the rule is technically not "hardwired" but "fastened in place". I am not an expert, but I can find experts claiming that an appliance which is attached to the structure, and always plugged in, counts (against the 50%) even if it's not hardwired. Certainly you would be grossly violating the spirit of the rule, regardless of how you interpret the letter. Nov 30, 2023 at 4:53
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    In support of @GlennWillen's comment, breaking the spirit of the law, even if not the letter may get you by. Until it doesn't and your house burns down. Just not worth it IMHO.
    – FreeMan
    Nov 30, 2023 at 13:35

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