Electrically impossible happening...and rather worrisome

I'm struggling to make sense of something that just started happening. I have 4 recessed lights in a room, all controlled by one switch via one load wire. The bulbs are standard, dimmable LEDs (ie not smart bulbs). They've been in place a few years, with a UPB switch. I replaced the switch with a Zooz S2 dimmer a couple days ago.
Since doing so, I've had a couple instances where only one light went on.
That should not happen unless 3 bulbs are dead since they're all connected in parallel.
However, turning off and back on, all 4 went on.
This didn't ever happen with the previous switch.

About the only thing I can think of is that it's a bad connection and occasionally not providing enough current for all 4 bulbs to light up.

Anyone have any other ideas?


Likely the bulbs are fairly incompatible or you want a load resister on them. Try adding one of these https://www.amazon.com/Lutron-LUT-MLC/dp/B01E9F084E


Would you expect that to be different with a different switch ? Trying to understand why it just started happening when I swapped switches.

Because every switch can be different and not every bulb is compatible with every switch.

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Is this dependent on the dim level selected?

Did you replace a Switch with a Dimmer?

If Yes, then the technology is quite different and the load (watts/amps) will make a difference for a dimmer especially. Try swapping one bulb with an old school incandescent and see if that increased load allows them to work. If Yes, then you can get the Lutron component suggested above.


Note: I automatically assumed dimmer

Correct replaced UPB dimmer with zwave dimmer. Should have said that explicitly.

Ok I would try the load resistor I posted above. If that's not it, return it and get compatible bulbs.

Not that I noticed so far . It doesn't seem to be the case that initially one goes on and then the others as it gets brighter. That would make more sense. But I'll test this out more systematically.

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Sorry, can't resist... "Electrically impossible happening"

"If it happens it must be possible."



This is another bypass as well:



Your wording suggests you are starting them low and "slowly" increasing the dim level. If this is the case then I would try:

  1. start at 100%
  2. if the bulbs that don't come on are always the same, swap them with the one that always comes on. This will show if it's wiring or not.

What brand of LED's do you have?

Electrically its not obvious what could be the cause. You could try the above mentioned load resistor but I doubt it will make a difference with you Zooz dimmer.

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Also make sure you are not exceeding the max load.. but in your case with only a few lights probably not an issue.

I know. :slight_smile: I'm a former EE. But I'm thinking simple circuits - bulbs in parallel, can't have just one getting power.

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Exceeding max not an issue - 4 led bulbs - 65W equivalent - so probably about 11watts each. (Have to check - they've been up there a long time).

Not sure what brand - I've used a few over the years.

I do have a few LDS stabilizers (bypass modules) I can try, but I'll see if I can consistently reproduce it first.

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There are quite a few type of dimming circuits. You are unlucky enough to have one that's not compatible. PWM, Leading edge, trailing edge etc...


Just looked up this dimmer (Zen77). There's no minimum load for it - but I suppose there could still be a compatibility issue.

But if there was a minimum load requirements, you already know the dimmer is "on" as one light is illuminated.

Since the dimmer is able to light at least one of your LED lights I'm guessing the compatibly issue is more in the LED than dimmer. Having said that I've never heard of an LED light not going on when full power is applied.

Have you tried starting at 100%?


Found this on the Zooz support site.. but again this is for flickering so not likely your issue.. thought I'd post it anyway..