0

I'm trying to swap a combination switch for two separate smart switches (Meross Smart Dimmer).

It seems, going by the existing switch wiring that the white 'neutral' wires are actually providing the load to the lights that they control. If that's correct, it leaves me without a neutral wire for the smart switches.

There is a separate unused cable in the box - can this be used in some way to provide the neutral?

While I've installed another of these switched in another room without issue, I've tried a number of combinations here but none seem to work. Any advice appreciated.

Desired trade (combination switch for two smart switches):

enter image description here

Existing combination switch wiring:

enter image description here

Available cables/wires within box (only thee two on right were used):

enter image description here

Side of combination switch showing snapped off tab (other connections on opposite side read A1, A2, B1 (only A1 and B1 were connected):

enter image description here

1
  • 2
    To know your options here, you need to identify the third cable. Does it have neutral? Your combination switch is wired in what we call a "switch loop" which has hot and switched hot only, connected at the light fixture. You can rewire, but it means cutting your drywall and running more cables. You could also use a no-neutral smart switch solution, like smart bulbs or Shelly. Jan 19 at 22:42

2 Answers 2

3

The key problem is that the power is coming into the switch via a switch loop. That is perfectly legitimate, but it means that white is not neutral. The other cable might be of help, if it is on the same breaker as the switches/lights, but rewiring to take advantage of that could get a little complicated.

The easiest solution, generally speaking, is to find a smart switch that does not require neutral. Every smart switch needs to get power from somewhere:

  • Neutral - best if available
  • Battery - needs to be changed periodically
  • Leak through lights - great with incandescent, varies between OK, "dim when off" and "crazy flashing" with LEDs.
  • Ground - only permitted under very limited circumstances and only when designed/listed as OK

I also have some concerns about your switches. While they appear to be ETL/Intertek listed, I couldn't find the model # in the ETL lookup page. Which is not an absolute guarantee of a problem, but not a good sign. In addition:

  • Web site and manual both seem a bit too Chinglish, but could be I'm too picky.
  • Wire colors a bit "off" in various places
  • 90-125VAC is unusual but OK. 50/60 Hz. is very unusual for a US-specific product of this type.

All just seems a little "off" to me. But that being said, it won't work anyway because you don't have neutral, and many similar products from major manufacturers will have the exact same problem.

2

On a tandem switch, "the tab" is for the usual situation where you have a black always-hot wire feeding both switches. Leave the tab and you can just hook one wire and be done.

With the tab broken off, the two switches are completely independent, and wire exactly like two normal switches.

However, these are both "old school switch loops that don't have neutral". The black and white wire are "always-hot" and "switched-hot".

By Code, the white should be always-hot (to make it more obvious that it's not neutral) and more recent Code requires it be marked with black electrical tape to flag it as not a neutral. That is because black-white is how cables come.

The rule with neutral is "You can only take neutral from cables that already have hot wires running to the switch". In your case, all 3 of the cables are totally isolated from each other - they do not share anything. So you cannot cross any wires between them. (except safety ground, which is always connected between all wires, all devices and a metal box).

This means you're out of luck with these switches.

I have no idea what the third cable is, and that might bear investigating. I gather it's not connected to neutral, or else your experiments would have "worked" (unsafely/illegally) and you would have never asked your question here. My guess is "it's a third switch loop" to a switched receptacle or light currently not working. Classically someone replaces receptacles, does not pay attention to those tabs, and effectively shorts out the switched receptacle function, making it always-hot and the switch inoperative. Sound familiar?

Anyway, if you can figure out where that third cable goes and re-task it to be "power supply hot/neutral", then you can convert this box into the normal "power into the switch box; lamps at end of runs" arrangement. You will need to cap off/isolate the hot-neutral that no longer feeds the lamps.

That would leave you without a switched receptacle: "Boo Hoo" :) If you have a working light built into the ceiling that is operated from the switch, Code is satisfied and get rid of switched receptacles.

Lastly, stop experimenting. The problem is your "win condition": you will stop experimenting the moment you hit a combination that works, right? Well, there are many combinations that will "work", and then kill you. You have the good sense not to attach neutral to ground... that helps a lot.

3
  • 1
    No comment on the lack of UL stamp on those switches? You're slipping... ;)
    – FreeMan
    Jan 20 at 13:46
  • @FreeMan probably because I already covered it. I'm 98% confident the ETL is fake. It seems they're bolder about making fake ETL (which is a good listing if real) than UL. Jan 20 at 15:11
  • @FreeMan yeah, didn't see a reason to belabor it, and anyway, if it's fake it's flawless, a huge change for Meross. All the right marks and none of the wrong ones. Jan 20 at 20:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.