Light dims for several min, then normal

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  #1  
Old 10-20-07, 11:26 AM
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Light dims for several min, then normal

I have an overhead kitchen light that occasionally (several times per week) will dim for several minutes, then return to regular wattage.

After this was going on for a while, I replaced the light with a brand new one, and put two 60W bulbs in (what it says you should use). The same thing happens. The wiring looked good when I was replacing the light although I did not spend a lot of time inspecting it.

The dimming does not occur always when something else is turned on and it is not on the same circuit as any big appliances.

Thanks for your thoughts. Bryan
 
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  #2  
Old 10-20-07, 12:51 PM
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Sounds like a loose connection. Could be anywhere on the circuit with the lights.

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  #3  
Old 10-20-07, 01:14 PM
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When you say a loose connection, do you mean that I should check all the wires in the light and the ones in the circuit that lead up to that?

If it is a loose connection, why would it dim for a couple of minutes and be normal for a while, then dim again?

Thanks.
 
  #4  
Old 10-20-07, 05:21 PM
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Yes, I mean you should check all the connections.
It's a poor connection. As it heats up it makes better contact. It would not even suprise me if you found a burnt up wire nut. It could be arcing where the connection is loose.

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  #5  
Old 10-20-07, 05:41 PM
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I will check the connections tomorrow.

However, the light is normal when it is first turned on, then after some time it dims for 5 minutes, then goes back to normal. Not sure if that is consistent with "warming up".

Bryan
 
  #6  
Old 10-20-07, 09:23 PM
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Warming can cause expansion. Expansion may decrease contact.When it cools contact is restored to more normal flow.
 
  #7  
Old 10-20-07, 10:37 PM
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There are many things that are not "big appliances" but that still draw enough current to cause bulbs to dim. Clothes irons, space heaters, vacuum cleaners, sump pumps, pool pumps, etc.
 
  #8  
Old 10-21-07, 07:23 AM
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OK, here is how it is wired, I believe correctly and all the wire nuts are tight. I will try to be specific in all the wires. I have tested each with a meter.

TWO electric cables coming in, each with a ground, white, and black. One obviously comes from the switch and one is "hot". The light is at the end of a circuit.

One white and one black are together with a wire nut (from different cables)--black one is hot, white one from switch. Then the other white and black (obviously again each from a diff cable) attached to the light (black from switch, white from hot).

Again, all the connections were "tight". I did notice the ceiling had some black marks from the previous light. Not sure if that means that it is getting too hot. It is a light we use a lot since it is in the kitchen. THanks.
 
  #9  
Old 10-21-07, 08:28 AM
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Did you redo all connections with new wire nuts? The overheating is troubling. What is the condition of the insulation on the wires at the light's box. Have you checked the switch box connections. You might try replacing the switch.
 

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  #10  
Old 10-21-07, 08:59 AM
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Is this a 'canned' light fixture with thermal protection in it?
 
  #11  
Old 10-21-07, 09:01 AM
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Originally Posted by ecman51` View Post
Is this a 'canned' light fixture with thermal protection in it?
Good question.

What type of fixture is it?

steve
 
  #12  
Old 10-21-07, 10:33 AM
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The wire casings look normal and in good condition. No overheating marks.

THe light fixture is one with insulation and the tin foil like stuff.

Keep in mind that I had an older fixture that was doing this, then I just bought a new fixture from Lowes and it still does the same thing.

I took a look at the switch part and that all looks good. I replaced the switch a couple of months ago without a change in the dimming.

Could there be a "short" in the switch wires (which aren't hot until the switch is flipped, then as it heats up it causes dimming?
 
  #13  
Old 10-21-07, 11:17 AM
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Sounds like you have a loose or coroded connection somewhere on the circuit.

I recommend that you get a electrician to check it out.

It can create a hazard.

steve
 
  #14  
Old 10-21-07, 01:35 PM
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The problem could be in any box anywhere on the circuit. It could even be in the breaker box. It could be the breaekr connection to the bus. What type of panel do you have?
 
  #15  
Old 10-21-07, 02:22 PM
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I have replaced all the wire nuts and made sure they are secure. I also replaced the wire nuts in the other light on the same circuit and made sure that all the connections were tight. Hopefully that will solve the problem, I am going to use the light and see if it dims again.
 
  #16  
Old 10-22-07, 05:20 PM
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Another area to always look for in any light fixture with a socket is in the socket itself. Most use rivots to join the incoming wires to the socket. Make sure when ever you have dimming, flickering, or even bulbs that keep prematurely burning out - that you do not see brownish arcing marks on the socket next to these 2 crimps.

Also make sure you are not using some off brand bulb that will not allow the base of the bulb to go all the way down into the socket.
 
  #17  
Old 10-22-07, 05:40 PM
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I appreciate all of your comments.

I have used the light for about a day and this morning it seemed to dim briefly, but then went back to normal right away. It has yet to dim the rest of the day. Dare I say that it could be fixed.

Could there be a short in the wires from the switch to the bulb that could be doing this?

The socket area on the fixtures looked fine when I was putting the light up, and the fixtures are new.
 
  #18  
Old 10-23-07, 04:20 PM
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Most likely heat from the current flow is causing something to open up, that should not be. Then when it cools down it makes better contact again. There could even be arcing going on. I'd want to get to the bottom of this.

I'd look at the switched circuit, then the ENTIRE circuit. Switch, switch connections (no back stab I hope, as that right here could do it), the rivots inside the light socket (you can see these when the bulb is unsrewed.) Then I'd make sure that circuits hot and neutral wires are tight in the panel box. From there I'd move on to every outlet on the circuit to see if backstabbing was done, and or check for loose wires connected to the outlets.
 
  #19  
Old 10-24-07, 05:22 PM
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Thanks for the thoughts again. Here is a little update and explanation, and then hopefully I can get your thoughts of where to start.

The circuit has several outlets and three overhead lights on it, the light I am talking about is the last on the circuit. The middle and first light NEVER dim, just this last one.

After taking it all apart and using new wire nuts and tight connections this weekend, the light is much better. It has only dimmed once (and that was only for about 5-10 seconds instead of minutes). Also, it was not nearly as dim as previously. So, now it has only dimmed once since Sun and VERY BRIEFLY, like a matter of seconds--is that long enough to have something "cool".

The switch does have the wires stabbed into the back, should I change that first to wrapping around the screws? Also, does the improvement suggest that it has something to do with the connections in the socket?
 
  #20  
Old 10-24-07, 05:39 PM
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The circuit has several outlets and three overhead lights on it, the light I am talking about is the last on the circuit. The middle and first light NEVER dim, just this last one.---------------

Plug a table lamp into the recepts. and see if it affects there----

Trouble shooting tip #1---Loose connection areas are almost always either the first one that doesnt work---or the last one that DOES! If the affected light doesnt show any obvious issues---try the one before it.. Keep in mind -Just because it is at the end of the room ..doesnt mean its the last on the circuit.

Just appease me for a second----This isnt a Flourescent light is it?

Also--check the tabs at the bottom of the sockets to make sure they havent flattened out---ON ALL 3 Lamp locations....
 
  #21  
Old 10-24-07, 06:15 PM
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It is not fluorescent.

I will check the tabs on all the lights.

I have already taken a look at the previous light in the circuit and replaced the wire nuts. I did not look at the first light in the circuit--should I do that? I didn't think that could occur since the middle light never dims, and so I figured it couldn't be from the first light.
 
  #22  
Old 10-24-07, 06:47 PM
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Certainly......

Are you judging first, middle , last ---By position on the ceiling?

They may not be WIRED in order like that.
For example----With unknown explanation.... My hallway starts 8 feet from the circuit panel...But yet the first light in the hall is the last on the circuit. It doesnt always make sense....
 
  #23  
Old 10-24-07, 07:17 PM
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Change the wires on the switch to the screws. I suggest that you then procede to change all switches and outlets from the backstab connection to the screw connections, otherwise you will be continually fighting problems like this.
 
  #24  
Old 10-27-07, 03:34 PM
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Thanks again to all who have replied. To answer a few of the questions posted:

I'm judging that it is the last in the circuit because it only has two "wire complexes" coming into the box--one from the switch and the other from the previous light. If it were the first or second light, wouldn't it have 3 wire complexes--ie. one from the breaker or previous light/outlet, one to the switch, and one on to the next light.

I have redone the switch aspect of it (onto the screws) and again rechecked the wire nuts at the light, which are all tight. I then changed the light bulbs to make sure that wasn't it. I've used it for a couple of hours and no dimming, so maybe this worked (or maybe that's just my hoping so).

I will post again if it dims and see if anyone has ideas.

Also, just for my curiosity--why don't people like the push backs? I've redone several switches and outlets and like them from an installation standpoint (they are obviously much easier) and have never had problems with them (this switch was not redone by me). Are they just not tight? Albeit the outlets that I've used have a screw so that when you push in the wires you use the screw to make it very tight.

Bryan
 
  #25  
Old 10-27-07, 03:43 PM
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[QUOTE=bryansauer;1248987Also, just for my curiosity--why don't people like the push backs? I've redone several switches and outlets and like them from an installation standpoint (they are obviously much easier) and have never had problems with them (this switch was not redone by me). Are they just not tight? Albeit the outlets that I've used have a screw so that when you push in the wires you use the screw to make it very tight.

Bryan[/QUOTE]

In all honesty, I have used them also. After all they are engineered and obviously approved for use. I always make sure that if I am too lazy to pigtail to the screw and choose the 2nd wire to go into a backstab, that I have it so when I push the switch back into the box, the wire is exerting forward pressure into the backstab.

Regarding the outlet that has the backstab with the screw to tighten it? Not the same thing. That design is what circuit breakers and GFCI's employ, and these actually tighten a plate inside to squeeze the wire. A cheap true backstab just uses springloaded metal.
 
  #26  
Old 10-27-07, 06:07 PM
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The reason we don't like is because when someone finds a loose connection at a receptacle it is 99% of the time a back stab. You almost never here of circuit that is half working bacauseof a loose connection under a screw connection. It is either a bad backstab or a loose wire nut.
 
  #27  
Old 10-27-07, 06:40 PM
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A back stabbed connection holds because of a spring. Over time as the metal expands and contracts due to the changing current the spring weakens. Eventually it fails. The failure is usually under a heavy load, such as a vacuum cleaner, iron or hair dryer or other high current device. For some reason it is also usually the neutral.
 
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