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I'm hoping these symptoms will be obvious to someone who knows better:

I'm adding smart dimmers in a fairly new (2013) house in Canada. Two are replacing regular dimmers in a four-gang box which controls four separate light fixtures with no other switches. There's five wires coming into the box - the four lights plus the supply. All the existing switches just use the live but I do have neutrals which are all bound together. It all seems pretty modern and simple and I've installed smart switches in similar boxes with the same config.

Here's the problem - when I replace the two dimmers with the smart dimmers both work but one switches on both fixtures instead of just the one it handles the load for. The other just switches on its own load, as I'd expect. I've checked, double-checked and re-done all connections, swapped the two switches, tried them on their own and always end up with the same results. Probably also relevant is the fact that when both sets of lights come on in response to one switch, they're clearly under-powered (flickering) and turning on the second switch adds more juice and both run as normal, so it seems like somehow the live from switch one is being shared to both sets of lights?

The smart dimmers have four connections which I'm connecting as follows:

  • Load (red) to the fixture black wire
  • Live (black) to the common live (blacks) coming into the box
  • Neutral (white) to the common neutrals/whites coming into the box
  • Ground to a ground on the box
  • The neutral from the fixture wires goes to the common neutrals

I'm guessing there's a mixup somewhere and I'm doing something dumb. Any ideas? Many thanks in advance... :-)

EDIT: Adding some pictures. Thanks in advance. This is with just one smart switch - this setup works fine. If I replace the manual dimmer (spot #3) with another smart dimmer we get the issue.

First two switches are irrelevant I think - removed for visibility

I believe middle cable of the five is supply

Zoomed into the back of the smart switch - Treatlife Smart Dimmer - https://www.amazon.ca/dp/B07YKFSWJN

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    What make and model are the smart switches in question, and can you post photos of the inside of the switch box please? – ThreePhaseEel Dec 6 '20 at 20:40
  • Pictures, pictures, pictures!!! – FreeMan Dec 6 '20 at 22:10
  • Sorry, I was sick of taking it apart and putting it back together again with runs up and down to the breaker! Pics added above. Let me know if anything needs explaining. – user3019595 Dec 6 '20 at 23:51
  • @user3019595 -- it seems that your edit for adding the photos didn't "take"...try it again? – ThreePhaseEel Dec 6 '20 at 23:52
  • Yeah my bad - thought I could add them to a comment - just added in an edit above. – user3019595 Dec 6 '20 at 23:57
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I'd junk those smart-dimmers and get ones that are less...cheesy

The first problem you have to address is that you have Cheesy smart dimmers that never went through the gauntlet of testing required by CSA/UL/... and thus can't be reasonably guaranteed to not do untoward things to you, like try to light your house on fire. Since your wiring configuration looks utterly conventional here, I'd try with a better (i.e. not so Cheesy) set of smart dimmers and see if you're still getting the misbehavior described.

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  • What others would you recommend? It still seems an odd issue that would be more to do with my wiring but OK. – user3019595 Dec 7 '20 at 0:13
  • @user3019595 -- my starting point would be to shop at your local electrical supply house instead of Amazon/Ebay/... If you want a brand name, my inclination would be to go with the Leviton stuff if WiFi was important to you, and with either Insteon or Lutron gear otherwise – ThreePhaseEel Dec 7 '20 at 0:18
  • Yeah I get you. Trouble is 4x the cost plus extra dongles and hubs is a pain. Lutron also seem to do really heavy price protection. I guess it's one way to "compete" with China, although I assume all their stuff is made there too, quite possibly even with the same manufacturers. – user3019595 Dec 7 '20 at 0:33
  • @user3019595 -- UL's gotta pay their bills too... – ThreePhaseEel Dec 7 '20 at 0:38
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    @user3019595 Well, it's illegal to install non-approved equipment, NEC 110.2, so I would say to stick to UL approved units. I think these units are interfering with each other anyway. That's what happens when amateurs design stuff blind into a foreign market, pinching pennies as they go. (US design houses "eat their own dogfood" i.e. install their prototypes in their own offices and homes. Chinese can't since their power is incompatible.) – Harper - Reinstate Monica Dec 7 '20 at 2:04

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