AFCI breakers and Dimmers

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Bama_Electrical

Senior Member
Location
Alabama
Occupation
Electrician
Customer called and ask me to troubleshoot some flickering they are having with dimmers. 3 different circuits, all on AFCI breakers with Legrand dimmers. If the lights are dimmed down on any of the 3 different circuits, the lights will flicker. If the dimmers are set to full power, no issue. Tracing confirmed there is not tie in at all with the 3 circuits as well. Any thoughts?
 
Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
It's probably just an issue of compatibility between the dimmers and lamps, especially if they are all the same brand.
Some dimmers have a low-end trim that you can adjust, though this may mean they can only dim to maybe 10-15% of full. Trying a different brand of lamps is another easy experiment.
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Bama_Electrical said:
3 different circuits, all on AFCI breakers with Legrand dimmers.
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AFCI breakers would have nothing to do with flicker. But have seen some Dimmers that would trip an AFCI breaker, usually the cheap Amazon off brand dimmers.

Seen with LED 2 factors, 1 Dimmer not compatible with LED or 2 Bulb not dimmable. Even with dimmable bulb and compatible dimmer most, LED have a dimming limit and below that threshold will flicker before full out. Some better dimmers have selectable min levels that need to be set to the bulb. It sometimes take a bit of playing to set the most dimming effect without flicker. LED as opposed with incandescent will have a minimum current for the driver and diodes to work, incandescent can be dimmed all the way to barely perceptible filament glow without flicker and some customers are use to that level and may not understand the limits of LED.

Most of these electronic dimmers and even dimmable LED have an FCC warning (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.
Flicker an undesired operation covered by this FCC criteria? Don't know. Is there anything that would cause flicker falling under the FCC criteria? Don't know for sure but suspect yes. But most times I've resolved flicker by above steps.
 
synchro

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Bama_Electrical said:
If the lights are dimmed down on any of the 3 different circuits, the lights will flicker. If the dimmers are set to full power, no issue.
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ptonsparky said:
All lights flicker if only one dimmer is turned down?
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Bama_Electrical said:
Only the lights that have dimmers flicker and they are Led’s
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ptonsparky said:
Ok. If two circuits are full bright and the third is dimmed, do they all flicker?
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Bama_Electrical said:
yes
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It sounds like the dimmers might be interfering with each other, and not just the LED lights on one circuit being susceptible to interference coupled from dimmers on another circuit. To confirm this, a suggestion is to replace one of the dimmers with a mechanical switch and see if the dimmers on the other two circuits still cause the lights now on the mechanical switch to flicker. If it no longer flickers, then apparently each dimmer is interfering with the operation of the other dimmers.

Another thing for diagnosing the problem would be to put an incandescent bulb on one of the circuits (assuming the lights have replaceable bulbs). And then see if the flickering and interaction between the circuits changes or it does not.
 
kwired

kwired

Electron manager
Location
NE Nebraska
ptonsparky said:
I wish my memory was longer than my...little finger.
Doesn't one of these dimmer mfgs have an add on device that helps with this issue.
I believe one of our Mods has had success with it.
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Minimum load capacitor. This is what Lutron calls their unit, I believe others have similar units.
 
B

Bama_Electrical

Senior Member
Location
Alabama
Occupation
Electrician
synchro said:
It sounds like the dimmers might be interfering with each other, and not just the LED lights on one circuit being susceptible to interference coupled from dimmers on another circuit. To confirm this, a suggestion is to replace one of the dimmers with a mechanical switch and see if the dimmers on the other two circuits still cause the lights now on the mechanical switch to flicker. If it no longer flickers, then apparently each dimmer is interfering with the operation of the other dimmers.

Another thing for diagnosing the problem would be to put an incandescent bulb on one of the circuits (assuming the lights have replaceable bulbs). And then see if the flickering and interaction between the circuits changes or it does not.
Click to expand...
To add a little more info on the home. The main service is 400/320 and is split to 2 different 200 amp mains. So I was able to do some additional testing on the circuits. I had already replaced one of the rooms with a standard switch and those lights no longer flickered when the other 2 rooms were dimmed, however those 2 rooms still flickered when the other room was dimmed. What’s odd to me is that each of those rooms are on separate panels, not just different circuits.
 
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