Issue with LED Wafer light and Bath Fan

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Little Bill

Little Bill

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Tennessee NEC:2017
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Semi-Retired Electrician
I'm trimming out a new house that I wired. In one of the baths I have an LED recessed light over the tub and a bath fan near it. I noticed that if the LED is on and I turn on the fan, the light blinks or goes out briefly. It also does it when I turn the fan off. This only happens with the on/off of the fan. After the initial blink the light stays on.
This is how the switching is set up:
3G box with switch for LED light, sconce/vanity light, and bath fan. These are all single pole switches with a common hot.
I didn't have time yet to look into it much, such as changing out the LED, but thought I might get some thoughts before looking into it.
 
Apparently there's a voltage transient induced when the fan is turned on or off (that's probably stating the obvious). Maybe changing to a non-dimmable LED bulb might help, assuming that there's a dimmable bulb in there now and that its dimming detection circuity is being falsely triggered by the transient.
 
Little Bill said:
I'm trimming out a new house that I wired. In one of the baths I have an LED recessed light over the tub and a bath fan near it. I noticed that if the LED is on and I turn on the fan, the light blinks or goes out briefly. It also does it when I turn the fan off. This only happens with the on/off of the fan. After the initial blink the light stays on.
This is how the switching is set up:
3G box with switch for LED light, sconce/vanity light, and bath fan. These are all single pole switches with a common hot.
I didn't have time yet to look into it much, such as changing out the LED, but thought I might get some thoughts before looking into it.
Click to expand...
Well. You obviously would have put it on another circuit if available. Did you try a new switch? How about putting it on the switch with tha vanity light? And try an incandescent. . I have a ceiling fan with led bulbs in it and there is a slight time delay between turning the switch on and the bulbs lighting. Bugs me, but i wrote it off to them being leds
 
qcroanoke said:
Well. You obviously would have put it on another circuit if available. Did you try a new switch? How about putting it on the switch with tha vanity light? And try an incandescent. . I have a ceiling fan with led bulbs in it and there is a slight time delay between turning the switch on and the bulbs lighting. Bugs me, but i wrote it off to them being leds
Click to expand...
I discovered this late in the day and didn't have time to try anything yet. Each item, vanity, wafer light, and fan, are on their own switch.
 
Little Bill said:
This is how the switching is set up:
3G box with switch for LED light, sconce/vanity light, and bath fan. These are all single pole switches with a common hot.
I didn't have time yet to look into it much, such as changing out the LED, but thought I might get some thoughts before looking into it.
Click to expand...
Little Bill said:
I will try a different wafer light tomorrow. I don't have a different brand though, I may have to get one to try.
Click to expand...

Do you have a 3-wire cable going to both the LED light and fan with a shared neutral? If so, and you have another wafer light just like it, you might try connecting that wafer light to the switch with a comparable length of 2-wire cable and check if that light will also blink with the fan switch. This would be to check if there could be any issue with coupling between the wires or a voltage drop on the common neutral within the 3-wire cable when the switch is toggled.
 
synchro said:
Do you have a 3-wire cable going to both the LED light and fan with a shared neutral? If so, and you have another wafer light just like it, you might try connecting that wafer light to the switch with a comparable length of 2-wire cable and check if that light will also blink with the fan switch. This would be to check if there could be any issue with coupling between the wires or a voltage drop on the common neutral within the 3-wire cable when the switch is toggled.
Click to expand...
No, all 12-2 NM, each fixture/device has it's own switchleg and no shared neutrals. The fan and wafer light are not an all-in-one unit. The fan just happens to be located near the light.
 
UPDATE:
I put a ferrite choke on the load conductor from the switch for the fan. It didn't change anything. I don't know if you should put the neutral through the choke along with the load. Also don't know if I should have put the choke on the light load conductor.
I also swapped the light. It was the same brand as I didn't have a different brand. Only thing that changed after swapping the lights was instead of the light blinking on both on and off of the fan, it only blinked when I turned the fan off.

There is another bath down the hall with the same light and same fan. I thought I would see if the light blinked when that fan was turned on/off. But the light and fan were both on the same switch per customer's request. With the fan and light coming on together, I see no blinking. If the customer is willing to put up with the other bath's blinking light, I will leave it as is as it doesn't blink everytime. If not, I may ask if I can switch them together like the other bath. Or if they insist on fixing it, I will just get a different brand light.
 
Something that could be tried is putting an RC snubber across the light switch output and the neutral. Normally you'd put one across the cause of the transient, which is the fan. But by doing that I think the snubber itself could draw a pulse of current when the fan is turned on, and that might cause the light to blink. Of course it could be tried to see what it does.
I don't know if this snubber has a low enough impedance to make a difference, but it's listed and probably available:

https://www.intermatic.com/Product/ET-NF
 
I noticed a strange thing too with an LED light the other day, I'm not kidding either .. Its not a light like your referring too but it is an LED,

This light is what warms the wax in one of those wax sense holders anyway the wife got it, so its good, any way the phenomena I notice was if I make a clap or bang within so many inches of this light it actually blinked ... Im wondering if my frequency of the loud bang interfered with the light frequency.

Maybe the signal noise of the fan interferes with the LED frequency.
 
Another C10 said:
I noticed a strange thing too with an LED light the other day, I'm not kidding either .. Its not a light like your referring too but it is an LED,

This light is what warms the wax in one of those wax sense holders anyway the wife got it, so its good, any way the phenomena I notice was if I make a clap or bang within so many inches of this light it actually blinked ... Im wondering if my frequency of the loud bang interfered with the light frequency.

Maybe the signal noise of the fan interferes with the LED frequency.
Click to expand...
I would think bad connection(s).
 
Another C10 said:
This light is what warms the wax in one of those wax sense holders anyway the wife got it, so its good, any way the phenomena I notice was if I make a clap or bang within so many inches of this light it actually blinked ... Im wondering if my frequency of the loud bang interfered with the light frequency.

Maybe the signal noise of the fan interferes with the LED frequency
Click to expand...
well ... I just had to check this morning and before I read what ptonsparky said, .... never mind it wasn't some mysterious phenomena I anticipated,
just a loose connection ... that adds to my personal human error status #7824.

oh, and scent not sense above. make that personal human error #7825.
 
Little Bill said:
UPDATE:
I put a ferrite choke on the load conductor from the switch for the fan. It didn't change anything..
Click to expand...

Further info shows ferrite chokes & wire turns can be selected for high-frequency noise, perhaps not as reactor for motor soft start.

If fan-motor inrush drops voltage below ~100vac listed input limits of residential-grade LED drivers, that may explain blinking off, especially on a high-impedance #14 circuit.

But synchro's post #12 may offer better explanation for LED blinking when fan is turned off.

Either way, it seems some of this problem would resolve with fan on separate-receptacle circuit, a high-efficiency Panasonic fan, or perhaps a 120-277v commercial grade LED wafer light.
 
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