Light Fixture Mystery (for me at least)


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Old 05-04-10, 09:19 AM
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Light Fixture Mystery (for me at least)

Hi all,

I'm having issues w/ a light fixture in my home. One morning I flipped the light switch, and the light came on and immediately went out. I have been unable to restore power to the fixture. Here is a list of symptoms, and steps I took in attempting to diagnose the issue:

1. Two of the three light bulbs were blown.

2. No circuit breaker was tripped. To be thorough, I tripped and rest the circuit that the light is on.

3. There is no GFCI on this circuit. Just to be thorough, I checked the three GFCI's in the house and none were tripped. To be extra thorough, I tested and reset each one.

4. I removed the light switch and tested the continuity w/ a multimeter. Checked out okay.

5. To be extra thorough, I tested the light switch inline with the circuit on. I got 115v a/c w/ the switch in the 'on' position, and 0v a/c w/ the switch in the 'off' position. I tested this with a multimeter switch terminal to the green ground in the box.

6. I removed the fixture from the ceiling and tested the wires w/ the circuit on, and the switch in the on position. Hot to common, hot to ground, and even common to ground: all 0v a/c.

So, what should I try next? Anyone have any idea of the likely cause?

Thanks in advance. Also, I apologize if any of my terminology is incorrect - I'm not exactly an electrician. If any clarification to the above is needed, please let me know.

Thanks,

-Mark
 
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Old 05-04-10, 09:39 AM
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It is probably a burnt or broken wire in this circuit. My first two suspects would be to check all of the connections in the switch box and in the light fixture box for tightness. If you have any backstabs (wire poked into hole) on the switches or receptacles, move those connections to the adjacent screws on the device. Remake wirenut connections -- sometimes those can burn off inside the nut and you can't see it until it's open. Check the wiring inside the light fixture box for heat damage.
 
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Old 05-04-10, 10:36 AM
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You may also have to check the splices in the ceiling box as well.
 
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Old 05-04-10, 10:56 AM
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Thanks for the quick replies.

I don't have any backstabs on the switch, and the connection to the switch is good, as verified by my multimeter.

I don't have any visible wire nuts or anything. Basically, in the switch box, just three wires coming down from the ceiling (or so it looks), and then three wires coming out of the ceiling where the fixture mounts to the ceiling.

So what's the next step? Go up into the crawl space and look for wirenuts/burnt wire?

Thanks,

-Mark
 
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Old 05-04-10, 11:45 AM
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Originally Posted by markn984 View Post
So what's the next step? Go up into the crawl space and look for wirenuts/burnt wire?
Quite possibly the best next step, if available. If you have Romex wiring and it runs through an attic type area, it's not unknown to have squirrels chewing on the wiring. I don't know why they like that outer coating so well, but sometimes you'll be able to find the issue by looking for the cooked critter.

Best of luck,
Rich
 
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Old 05-04-10, 11:56 AM
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Originally Posted by markn984 View Post
I don't have any visible wire nuts or anything. Basically, in the switch box, just three wires coming down from the ceiling (or so it looks), and then three wires coming out of the ceiling where the fixture mounts to the ceiling.
If you only have 3 wires coming into the switch box (hot, hot ground) then you have a switch loop which means you are getting power from the light box on the ceiling.

IF you have 3 hots then it is a three way. Although from your testing that doesn't seem to be the case.

1. Two of the three light bulbs were blown.
Just a thought, are you having any other odd issues? I am wondering if you have an open neutral which could potentiality burn up some equipment.
 
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Old 05-04-10, 12:04 PM
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I don't have any visible wire nuts or anything. Basically, in the switch box, just three wires coming down from the ceiling (or so it looks), and then three wires coming out of the ceiling where the fixture mounts to the ceiling.

So what's the next step? Go up into the crawl space and look for wirenuts/burnt wire?
You don't have enough wires. I assume you mean a 2-conductor cable with ground when you say "three wires". That means you only have one 2-conductor cable in each box. Normally there should be two cables in one of the boxes. That means there is probably a Jbox in the attic and the loose connection is there.
 
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Old 05-04-10, 12:14 PM
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[QUOTE=markn984;1723828]Hi all,

I'm having issues w/ a light fixture in my home. One morning I flipped the light switch, and the light came on and immediately went out. I have been unable to restore power to the fixture





" I tested this with a multimeter switch terminal to the green ground in the box".

***************************************************************

You performed an invalid test----You were reading "voltage- to - Ground" when you should have been testing between the White & Black/ Red wires. Your reading to Ground with a defective circuit suggests a an open-connection in the Neutral ( White wire) circuit-conductor.

One of the boxes must have two cables , and one of the cables ( in either the switch box or fixture box) must have a Black & White wire. The second cable could have Black / Red / White wires.

We need an exact description of the number of cables in the respective boxes, and the colors of the cable wires in each cable.
 
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Old 05-04-10, 01:01 PM
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No, it's not a three way. There's a white, black, and a bare copper. The bare copper is definitely the ground.

No other odd issues. Not even another outlet or light that's out.

Originally Posted by Tolyn Ironhand View Post
If you only have 3 wires coming into the switch box (hot, hot ground) then you have a switch loop which means you are getting power from the light box on the ceiling.

IF you have 3 hots then it is a three way. Although from your testing that doesn't seem to be the case.


Just a thought, are you having any other odd issues? I am wondering if you have an open neutral which could potentiality burn up some equipment.
 
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Old 05-04-10, 01:05 PM
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The light switch box has a black, white, and bare copper. Black to white gave me 0v ac. I then tested white to bare copper to see if the hot had any juice - got ac voltage on that test.

Sorry, I thought I included that in my original post. My bad.

[QUOTE=PATTBAA;1723897]
Originally Posted by markn984 View Post
Hi all,

" I tested this with a multimeter switch terminal to the green ground in the box".

***************************************************************

You performed an invalid test----You were reading "voltage- to - Ground" when you should have been testing between the White & Black/ Red wires. Your reading to Ground with a defective circuit suggests a an open-connection in the Neutral ( White wire) circuit-conductor.

One of the boxes must have two cables , and one of the cables ( in either the switch box or fixture box) must have a Black & White wire. The second cable could have Black / Red / White wires.

We need an exact description of the number of cables in the respective boxes, and the colors of the cable wires in each cable.
 
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Old 05-04-10, 01:17 PM
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Sorry about that. As I said below, I'm not an electrician and probably have the terminology wrong. Yes, I have one two conductor cable with a ground. I'll look in the attic for a junction box. Thanks.

Originally Posted by ray2047 View Post
You don't have enough wires. I assume you mean a 2-conductor cable with ground when you say "three wires". That means you only have one 2-conductor cable in each box. Normally there should be two cables in one of the boxes. That means there is probably a Jbox in the attic and the loose connection is there.
 
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Old 05-04-10, 03:50 PM
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Originally Posted by markn984 View Post
No, it's not a three way. There's a white, black, and a bare copper. The bare copper is definitely the ground.

No other odd issues. Not even another outlet or light that's out.
Ok, So you have a switch loop. Your hot wire is in the ceiling box and connects to the white going to the switch. Then the black in the switch box is connected to the other screw and goes back to the light. If you have a hot at the switch and nothing on the black of the same cable you either have a bad switch or the above mentioned break in the cable.

That or you have a buried j-box some place.
 
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Old 05-04-10, 04:04 PM
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Originally Posted by markn984 View Post
6. I removed the fixture from the ceiling and tested the wires w/ the circuit on, and the switch in the on position. Hot to common, hot to ground, and even common to ground: all 0v a/c.

So, what should I try next? Anyone have any idea of the likely cause?
We know it is a switch loop. Yet power has to come from somewhere. And it can't arrive as a hot feed in his light box, since there are only 3 wires in there. Ray must be right. They likely have a junction in the attic, where the hot feed and ground connection is.
 
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Old 05-04-10, 04:33 PM
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Okay since this is not a three way there are not enough cables for this to work. One of the two boxes would have to have two 2-conductor cables and neither does. That means power comes in at another box. The attic is one place but there are other possibilities. First order of business should be to try to visually trace the cables for the light and switch in the attic.

The other likely possibility (maybe more likely) is that once upon a time there was no ceiling light in the room. There was instead a switched receptacle. The light in the ceiling may come from that receptacle and the switch loop may go to the receptacle box.. Have you changed any receptacles lately?
 
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Old 05-04-10, 05:23 PM
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It's kind of funny how one can start making mental images of a situation when nothing was even said. For some reason I started assuming there is this attic directly above the room with maybe even a junction box fairly close to the light box.

Maybe we could help guess better if we knew the layout of the house - if one or two stories, and where the switch and light is.
 
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Old 05-04-10, 07:31 PM
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The house is one story. There is an attic above the light. The light switch is on the wall, about 7 feet from light, which is on the ceiling.

No change of recepticles or any work since the place was remodeled 10 years ago.

I will try to go into the attic tomorrow and look around. It won't be pleasant though - insulation was blown in there when it was remodeled, and I'm sure it'll be a mess.

Originally Posted by ecman51` View Post
It's kind of funny how one can start making mental images of a situation when nothing was even said. For some reason I started assuming there is this attic directly above the room with maybe even a junction box fairly close to the light box.

Maybe we could help guess better if we knew the layout of the house - if one or two stories, and where the switch and light is.
 
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Old 05-04-10, 08:23 PM
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I'm leaning more toward a connection of a switch loop and power to the light in a receptacle Jbox the more I think of it but it is good to check the attic for a Jbox first.
 
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Old 05-05-10, 11:08 AM
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Well, we know that what you had worked, until it did not work. A loose wire nut is a logical conclusion. (But so might a poor back stab connection into an outlet, if that is how they tied in.) The matter is your place as remodeld 10 years go. What was remodeled? Was the switch and light done at that time? What about anything else nearby, electrical? And was say additional insulation added to the attic at that time?, to perhaps cover up where people crushed it from doing electrical work in the attic? If/when you DO go up in the attic, and say no insulation was added, check to see if signs of people walking up there. That alone may lead you to the jbox tie-in, if there.
 
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Old 05-10-10, 04:25 PM
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So we never get to find out the cause? - after all the effort put forth here on this thread?
 
 

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