I picked what I thought was a very fine brand of motion sensor, but the units are lasting only a few months. It's a 3-wire sensor: always-hot and neutral power the sensor, and switched-hot is passed through. As I read the documentation, I see them mention "Tungsten". I am driving LED "barn light" type products.

I could install one incandescent bulb to make the sensor happy. But when it burns out, it won't be quickly replaced, which would create the failure condition. So I want something that emulates a tungsten bulb, but is long-lasting. I'm thinking a resistor.

The question is, how do I find a resistor product that mounts on an electrical box it in a code-legal way, and is outdoors-safe? Is that even a product one could find? I'm not asking "shop for me" but I don't even know where to begin.

  • I use occupancy sensors on led fixtures. The sensors are for high bay lighting / universal voltage 100-277 vac I have not had them in for a year yet but have 16-20 units approx 3000 lumens / fixture. The sensors are not cheap ~ 50$ each, they can control multiple fixtures also. Will get info on the model tomorrow. I use the same sensor on 4 tube and 6 tube T5 lights most of these have been in use for over 6 years.
    – Ed Beal
    Aug 9 '16 at 7:21
  • 2
    Any resistor you use which is of a low enough resistance to successful emulate an incandescent light bulb is going to produce as much heat as an incandescent light bulb. Don't mount it in an enclosed box or you'll make a small oven and cause a fire...
    – brhans
    Aug 9 '16 at 11:41
  • How do you know it's the load resistance that's fouling things up? I'm not clear on how a higher resistance (far less current draw) would cause a problem. A motion sensor should last forever with nothing connected to the switched output. Also, what's an "LED barn light" ? -- that is, does it run off 120 directly? Aug 9 '16 at 14:26
  • I'm unclear on that too, since it's a 3-wire sensor with line and neutral. Maybe it dislikes line noise on the LED power supplies? I just know that the docs on this 8 month old unit say tungsten, incandescent, halogen, and do not name LED or CFL as permissible loads. I literally can't use incandescent; it's community space and some well-meaning soul will replace them with LED. Aug 9 '16 at 14:50

So you need resistors with an ampacity comparable to incandescent lightbulbs... have you considered incandescent light bulbs? I know, but hear me out here - we run incandescent light bulbs at the extreme end of their tolerance for the sake maximizing luminous efficacy. Backing down on the voltage, even a little bit, significantly increases the durability of the bulb. At 90% voltage, you're talking somewhere around 4x life span, 16x at 80% voltage... at 50% voltage, the bulb may well survive longer than you. So if you wire two incandescent light bulbs in series, you have a very cheap, low ohm, high wattage resistor, with a good life span (as long as vibration is low).

How to turn this into a code approved solution is left as an exercise for the reader.


If you decide to try a resistor look for a power resistor with terminals that allow bolts or stabs. You could then use ring lugs with bolts or stab on lugs to connect it.

Like this one: http://www.farnell.com/datasheets/1482672.pdf

Make sure it is mounted away from any other wiring in an enclosure that is ventilated. Depending on how much power it disapates, it could generate a lot of heat. Try to connect it into the circuit in an accessible dry location if it is possible.

Review Article 470 in the NEC for further requirements.

Good luck!

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