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I have six recessed lights in the kitchen. I bought six new LED bulbs to replace the old incandescents. I had to lower the socket an inch or two along the track in the recessed fixture in order to get the bulbs to fit.

The first two replacements worked fine. When I turned on the switch after swapping in the third, the circuit breaker blew. I turned the breaker back on, and it immediately turned off again. I removed the bulb, and turned the breaker back on. Then I turned the switch back on, and none of the ceiling lights lit. I've now cycled several times through the breaker and switch, and it's definitely not working.

I've removed the sheet-metal cover thing from the recessed lighting fixture, so now I have the light socket itself hanging loose by its wires. All the wires still look firmly connected.

I'm pretty sure electricity is still coming to the circuit, because the switch itself has a very dim light behind it that turns on when the switch is turned off, and when the breaker is turned on but the switch is off, that light still lights up (it turns off when the breaker is thrown).

I'd rather not have a simple light bulb switch wind up with a $200 electrician visit. What could have gone wrong?

ADDITIONAL INFO 1: I'm pretty sure the dimmer switch has failed, but also that it is not the only problem. With the switch connected (on or off), the breaker can turn on and off without any problem. I bypassed the switch entirely by just connecting past it (so the power is always flowing past the switch) and now the breaker pops immediately if I try to turn it on. (note that the first time I tried turning the breaker on with the switch still in the wall, the breaker popped, but now it doesn't. I think I fried the switch by trying to turn on the breaker a few times while it was still connected and shorted.)

So the switch seems dead, but even bypassing it entirely, there's still a short. So somehow I perhaps damaged the socket itself? I borrowed a multimeter from a friend. With the breaker turned off, I switched the multimeter to measure resistance and touched the leads to the input and output contacts on the back of the socket (no light bulb in it). The resistance wasn't zero, but it dropped from infinity down to a few dozen resistance-thingies. So perhaps the socket is damaged as well?

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a photograph of the fixture would probably help. –  Rory Alsop Dec 7 '12 at 10:03
    
When you removed the bulb and turned the breaker and switch back on, did the breaker trip again or did it hold but the lights just didn't come on? –  Tester101 Dec 7 '12 at 12:39
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Is this a circuit with a dimmer switch? If so, some LED bulbs will not be compatible with all dimmers, and at the least, you do need a dimmable LED. –  user558 Dec 7 '12 at 12:42
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Unfortunately, it's going to be very difficult for anybody to locate the fault through the internet. Locating the fault will take special tools, knowledge, and a good understanding of electrical principles (which I'm guessing you lack (no offense), based on you asking this question). It seems folks fear Electricians more than Dentists, but in this case calling an Electrician is the safest option. –  Tester101 Dec 7 '12 at 12:48
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keep in mind that if there are other fixtures in parallel, the OHMs reading will not be infinite because it is seeing the other bulbs. See my other comment below. –  shirlock homes Dec 8 '12 at 11:07

4 Answers 4

up vote 0 down vote accepted

It turns out there was a thermometer inside the cans that shuts off power if the light overheats. The thermometer was physically damaged when I was messing around up there. We replaced the affected can and the blown-out switch, and everything is good.

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What voltage do the bulbs operate at?

Here (in the UK) it is common to have recessed lights at 12V and at 240V.

In the case that the circuit runs at 12V it is common for the transformer to require a minimum current. This current will be drawn by a single 50W halogen bulb but not by three 6W LEDs - giving the symptom you describe.

If this is the case the optimum solution is to replace the transformer for an LED driver designed for the job.

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@shirlock homes answer is great but I wanted to one more possibility.

It sounds like the scenario is this:

  • With 3rd LED installed, turning switch on blew the breaker.
  • With it removed, it doesn't blow the breaker, but there's now no power to the other lights.
  • Before you put the 3rd one in, everything was fine with 1 & 2

It seems possible that the #3 bulb was faulty, which caused the short. (It is rare but I've put in screw-base light bulbs once or twice that had the tip & screw connected on the base due to a manufacturing fault).

You said your switch has a light- this makes me believe it's probably a dimmer. Even if it's not, though, a circuit overload can damage light switches. Dimmers especially. Because it takes some amount of time for the overload protection to do it's work, there is a very large amount of current flowing through the circuit once the ground fault occurs. The household wiring can handle this heat for a split second - but the internal contacts in a switch often cannot. They can fuse, or just break. It's perfectly plausible that the light on your switch would still light, but the switch itself not work.

I would swap out the switch and try another light bulb. You should also pick up a simple current tester like this:

enter image description here

This will let you easily test whether the switch input & output, and fixtures are hot, before you do anything.

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+1 Those little proximity testers are wonderful things. Anytime I go near a box, I wave one of them around it. I very much want to know if there is a live circuit in my vicinity before I poke my fingers in there. –  user558 Dec 7 '12 at 19:08

The answer is not a cut and dry one in your case. The troubleshooting is a process. You will need an understanding of a multiple light parallel circuit. You will also need a proximity type voltage tester and possibly a VOM.

Assuming the voltage feed starts at the switch (not always the case, but normal) you will need to verify input voltage at the line side of the switch with the switch in the off position. If you have voltage there, turn the switch on and verify voltage on the load side of the switch. At this point, a VOM is handy to test voltage across the hot and neutral and/or ground. If this looks good, proceed to the closest light fixture, and with the switch on, test the center hot tab in each fixture with the no-touch tester. In your case I would think you may not see any voltage based on your question. This could mean that you have an open neutral, an open hot, or at worse, a shorted hot to neutral/ground.

Since there are several possible reasons for your condition, it would take a lot of tutorial to explain every possible scenario. Assuming you do not see voltage at the fixtures, the basic technique for troubleshooting will be to start at the last known verified voltage point, then follow the wiring and check all connections in the junction boxes. Visually check the bulb sockets for broken or shorted metal tabs. This should be done with the power off at first, looking for obvious loose or disconnected wires, then with the power on using your voltage tester. Since this condition occurred after you adjusted the height of the sockets in the fixtures, I suspect tension on some wire may have pulled a wire out of a socket base or out of a wirenut in the j-box. Unfortunately, most can/pot lights have a built in j-box attached to the top of the fixture. This necessitates dropping the fixture down below the ceiling to access the j-box, or getting access from above. (attic).

Basically, you are following the circuit looking for an open or short, just like following a hose, looking for a water leak or stoppage.

This is not a hard job, but extreme caution must be taken when testing energized circuits. If you do not have good electrical skills, the proper test equipment, or a logical understanding of switched paralleled circuits, then this job is better left to a pro.

Maybe one of my buddies here on SE can add a good graphic showing this type of circuit and the test points. A simple line drawing showing the switch and junction points would be a great edit.

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+1 Exactly. Just start at the breaker. Verify that it is reset, as sometimes you need to push the switch firmly into place. I've got some breakers that look like you have flipped them into place, but need a nudge to make them active. If you determine that it is not bad, then move on to the next point in the chain. The proximity testers are nice, since they will beep/flash whenever they are close to an energized line. Always take great care with electricity. –  user558 Dec 7 '12 at 12:36
    
@Woodchips: +1, I've had breakers trip hard enough to unseat the internal magnets. Had to work them off and on a few times or remove them and slam them sideways on a bench to reset the magnets into position in order for the breaker to reset. –  shirlock homes Dec 7 '12 at 13:18
    
I've added some additional information in the original question. Looks like the switch is fried, but something else is definitely shorted, possibly the socket itself. –  Ben Dilts Dec 7 '12 at 22:07
    
I bet the dimmer is shot. I didn't know you had a dimmer on these fixtures. Not all LEDs are dimmable with a standard incandescent dimmer. Pull the dimmer out completely with power turned off, then recheck the resistance measurements at the socket in question. Anything below an Infinite reading with all the bulbs removed may indicate a short. You will see some resistance (measured in OHMS) with bulbs installed in other fixtures. –  shirlock homes Dec 8 '12 at 11:03
    
VOM = Voltage Meter, right? –  Shimon Rura Dec 8 '12 at 23:23

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