I bought some motion sensor switch. They don't come with screw mounts, just 18 AWG wires that pop out. The load is 2 light fixtures maybe drawing 200 watts total. It's on a 15 amp circuit though.

I also wired a timer switch with 14 AWG onto a 20 Amp circuit dedicated to X-Mas lights, the draw is about 300 watts when in use.

I've read there are some exceptions to wiring within the NEC regarding fixtures.

Am I rolling the dice? Or good to go?

  • Do you have the specs on the motion sensor, brand-make-model, picture? Commented Feb 12, 2019 at 11:23
  • 1
    This motion sensor has a UL/ETL/... listing, right? Commented Feb 12, 2019 at 12:43
  • I’m confused. Is this wiring all remaining inside the fixture?? Building wiring and internal fixture wiring are two different things. It sounds like you mean wiring between a motion detector and 2 light fixtures. Likewise the timer situation sounds like it’s wrong as written. The circuit breaker protects the wire, you can’t use 14 on a 20 amp circuit, nor 18 on a 15 amp circuit. Inside a fixture is different, outside the fixture tho-no exceptions.
    – Tyson
    Commented Feb 12, 2019 at 16:28

3 Answers 3


You are good to go. The NEC does not regulate manufactured equipment. In the US they are regulated primarily by UL, NEMA, and NFPA. In you case the motion sensor is what will regulate your connected load. In other words, it will probably burn up before the wiring is damaged.

Good luck and stay safe.

  • 1
    I agree as long as it has a UL listing it is both safe and code compliant.+
    – Ed Beal
    Commented Feb 12, 2019 at 17:40

Yes, you are rolling the dice. The 14 AWG wire is totally inappropriate for a 20A circuit, and now you must downbreaker to 15A to make that circuit safe. What were you thinking?

"Wait, how come the switch gets to use 18 AWG wire? That is proof positive that you are allowed to downwire anytime the expected load is low."

That's what you were thinking. That is reasonable logic, I must agree. However it is still wrong. Everyone needs to follow the rules. For you installing wire, you must follow NEC.

For the equipmemt maker building their equipmemt, they must follow product safety regs and UL's guidelines. UL then takes a specimen of the as-built machine and runs it through a series of torture tests. These tests are designed to simulate worst case scenarios. I suspect that the equipment has internal fusing, not actual fuses (that would cost money) but rather, intentionally narrowed traces on the printed circuit board. There is an art to handling mains voltage on a PCB.

Suffice it to say, UL is satisfied the 18AWG wire is safe, or they would not have listed it. And remember, part of the UL listing is the labeling and instructions. You must follow them when installing (NEC 110.3b) and the instructions say it must go inside a junction box.

Is your 14 AWG wire inside a junction box? No? Because that scenario - 14AWG wire in walls on a 20A circuit - has also been tested, and did fail.

  • Listed fixtures come with smaller wire all the time. If it is UL listed it would be safe I think every florescent lamp in my plant uses 18 awg wire to the ballast. The wire size from the device can be smaller If factory wired , but the circuit conductors still need to meet the breaker size.
    – Ed Beal
    Commented Feb 12, 2019 at 17:42
  • @EdBeal I’ve read this question several times, I’m not certain OPs staying inside the fixture.
    – Tyson
    Commented Feb 12, 2019 at 18:23
  • The first part defiantly is from the device. The second may be it is unclear. But the intermatic timers I have (st01 model) also have wires that are 14awg. As long as the load is less than the capacity of the timer I still think it would be legal.
    – Ed Beal
    Commented Feb 12, 2019 at 18:30
  • NEC 404.14 covers switches and they must be used within there rating. If the switch had a 20 amp outlet being controlled that would be a violation even if the load was 15 amp or less because a 20 amp load could be plugged in and that exceeds the rating.
    – Ed Beal
    Commented Feb 12, 2019 at 19:10
  • @EdBeal all those switch leads remain within the junction box, yes? Commented Feb 12, 2019 at 22:03

If the light come with 18 awg on a 20 A circuit- refer to the tap rule. Tap conductors are downsized as long as they are within the guidelines in the NEC. Fixture whips with downsized “tap” conductors shall not exceed 6’.

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