Light fixture buzzing

Reply

  #1  
Old 11-18-20, 04:28 PM
C
Member
Thread Starter
Join Date: Dec 2011
Location: USA
Posts: 378
Received 26 Votes on 24 Posts
Light fixture buzzing

I've got a light switch that controls 4 recessed ceiling lights. One of the lights blinks on and off. On time varies between ~3-10 seconds. Off time is ~1-3 seconds. Currently have LED bulbs, but was having the same problem with CFL and incandescent bulbs.

I removed the bulb from the offending fixture. With the switch on, I can hear buzzing from the fixture and the buzzing corresponds to the times listed above for the blinking.

Given the above, what's the first thing I should check?
 
  #2  
Old 11-18-20, 06:08 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,218
Received 103 Votes on 89 Posts
Check the connections in the junction box.
 
  #3  
Old 11-18-20, 07:23 PM
Z
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 5,548
Received 156 Votes on 139 Posts
With the timing, it could be a bad thermal switch on the can. It's supposed to click off if a too-high-wattage bulb is used. It doesn't sound like that's the case, but it could be causing the on-off-on flashing.
 
cartman voted this post useful.
  #4  
Old 11-18-20, 08:09 PM
C
Member
Thread Starter
Join Date: Dec 2011
Location: USA
Posts: 378
Received 26 Votes on 24 Posts
I removed the can, opened the junction box and the connections seem ok. Then I used a screwdriver to pry the tab at the base of the light socket up a little bit. Turned switch on and no more buzzing (no bulb in yet). Then I installed the bulb and no more light cutting in/out. So I guess the tab wasn't making good contact with the base of the bulb.

The wiring in this junction box is new to me; first time looking at a traditional can light (only light fixtures I've been this up close and personal with have been integrated LEDs). This is the last of the 4 lights on this run. The hot wire connects to a black jumper which runs into a gel(?) sealed plug that inserts to the side of the box (I assume this is what @Zorfdt refers to as a thermal switch?). A blue wire runs out of the thermal switch and connects to the light's black wire. The neutral wire connects to both the light's white wire and also to a white jumper that runs into the thermal switch.

So the hot and neutral both enter the thermal switch. When power is applied, the thermal switch is HOT, too hot to hold. I assume this is abnormal? I certainly don't feel comfortable sticking that back up in the ceiling and forgetting about it.



 
  #5  
Old 11-19-20, 10:43 AM
C
Member
Thread Starter
Join Date: Dec 2011
Location: USA
Posts: 378
Received 26 Votes on 24 Posts
Update: Pulling up the tab at the base of the light socket resolved the rapid on/off and buzzing, which revealed a much slower on/off cycle. I assume this is related to the thermal switch. Putting a heat gun to the switch, it's ~240*F. That's with the entire light fixture and junction box dangling below the ceiling. Also, there is no insulation in this ceiling (basement ceiling).

I pulled down the 3 lights on this switch. Two of them have the same/similar thermal switch, both of which are ~190*F. The other light fixture has no thermal switch or light-specific junction box; they ran romex to a regular junction box, then AC cable from the junction box directly to the light fixture. That fixture of course is fairly cool at ~70*F since I'm using LED bulbs. Bypassing the thermal switches on the other fixtures would solve the heat problem, but I'm guessing this may also be a code violation in that it's an incandescent recessed light fixture without any thermal protection device.

On a separate switch in the basement, there's another recessed light with a slightly different (but same general style) thermal switch and that's ~130*F.

So there's the issue of light going in/out with the super hot thermal switch using only a LED bulb. A couple of other thermal switches are very hot. And another one doesn't even have a thermal switch. Even if I could track down the specific thermal switch and replace them all, it seems like a waste of electricity to be heating these switches up - the coolest switch is still ~130*F after being on for a few minutes.

I'm thinking the easiest, most efficient and code compliant solution is to replace these fixtures with integrated LED fixtures.

Thoughts?
 
  #6  
Old 11-19-20, 10:53 AM
Z
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 5,548
Received 156 Votes on 139 Posts
When power is applied, the thermal switch is HOT, too hot to hold. I assume this is abnormal?
I would say so. Nothing in a standard can should produce any heat other than the bulb (or transformer if it's an LED setup). If it is a thermal switch, really it's just a temperature-sensitive switch that shuts off if the temperature gets higher than a certain point. I have no idea why it's getting hot itself -but probably should be replaced.
 
  #7  
Old 11-20-20, 08:45 AM
C
Member
Thread Starter
Join Date: Dec 2011
Location: USA
Posts: 378
Received 26 Votes on 24 Posts
Noticed something I don't understand. Maybe someone here can explain this. With the light switch off (circuit breaker on), I checked voltage at one of the light fixture's junction box. I measure 0v between hot and neutral, but measure 9.3v between hot and ground and also between neutral and ground.

My Klein NCV tester detects no voltage on hot, neutral or ground.

With circuit breaker off, the voltage between hot and neutral remains 0, and voltage between hot and ground and between neutral and ground drops to 0.17v.

How to make sense of this?
 
  #8  
Old 11-20-20, 11:32 AM
Z
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 5,548
Received 156 Votes on 139 Posts
Inexpensive (less than a few hundred dollar) digital meters have an issue with detecting phantom voltage . It's basically a tiny bit of high impedance voltage on the wire that the meter can detect, but isn't enough to actually do anything.
Many electricians recommend using either a neon tester, or analog meter as neither of these have any issue with phantom voltage.
In the end, nothing to worry about!
 
cartman voted this post useful.
  #9  
Old 11-21-20, 05:42 AM
C
Member
Thread Starter
Join Date: Dec 2011
Location: USA
Posts: 378
Received 26 Votes on 24 Posts
Inexpensive (less than a few hundred dollar) digital meters have an issue with detecting phantom voltage . It's basically a tiny bit of high impedance voltage on the wire that the meter can detect, but isn't enough to actually do anything.
Many electricians recommend using either a neon tester, or analog meter as neither of these have any issue with phantom voltage.
In the end, nothing to worry about!
So what would happen if touched hot wire to ground wire (where my digital meter shows ~9V between them) - would any current flow?

And why does this phantom voltage go away when the breaker is shut off, but not when the light switch is turned off?
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: