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prj 02-17-2010 01:51 AM

dual-switch light driving me nuts
My electrical experience is limited but I'm pretty good with simple things. We have a compact fluorescent ' low wattage can-light in a bathroom ceiling that is controlled by two switches (the bathroom has two entry doors; what they call a Jack & Jill bath). On and off over the past couple of years this light will work only intermittently. Sometimes it will go on, most often not. So I decided to get after it.

1. Changed out bulb..... no difference.
2. Got no voltage reading with multimeter at bulb socket. Tried with both switches in on and off positions.
3. Checked wiring within can from bulb socket back to junction box in ceiling..... looks OK, but I can't get into the junction box due to space and angle.
4. Checked voltage at both switches. Got readings (if I'm using the meter right) of about 25 volts across switch leads.
5. Changed out both switches....... no change.

I'm pretty much stuck now. What am I missing? Is it possible the socket itself is shorting out? To replace it without going back to the junction box I'd have to splice in a new socket, which is probably not to code. But is it dangerous if I use wire nuts filled with waterproof gel?


PaliBob 02-17-2010 05:48 AM

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prj, Welcome to the Forum

You didn't say anything about three way switches. Your light switches should have at least three wires so that either switch can turn the light on or off. Newer switches have a ground terminal but that is not required for the light to work.

Your 25V meter reading across the switch leads sounds to me like a ghost reading. Meter reading from ground to the switch terminal are more reliable.

Your new 3-way switch should look similar to the Pic but the Common terminal (different color) does not have to be the same as in the pic.

AllanJ 02-17-2010 07:25 AM

Don't screw the lamp (bulb) in super tight as this can deform the contact at the bottom.

You might want to give the contact at the bottom center of the lamp socket a bit more springiness. Turn the breaker off. Then pick at the contact to lift it a bit.

You need to find out where the power is coming it. There could be a loose connection somewhere including possibly at a receptacle in some room that the feed from the panel daisy chained through before getting to the light, possibly in the light fixture junction box (you did say it was a can light).

I would not be surprised if the switches are non-3-way switches wired up as an either-on light-on setup. In a small bathroom it would not be that inconvenient to turn both off to turn the light off. To convert to (true) 3-way you would need to string new, 3 conductor, cables.

Measuring voltage does need a jump to conclusions but measuring between two switch terminals is usually meaningless. Basic* voltage measurements are done between (preferably) hot (including a switch terminal) and neutral or between hot and ground and you have to assume that the neutral or ground is correctly connected down at the panel which is the jump to conclusions.

* Experienced persons can make use of voltage measured between two switch terminals.

prj 02-17-2010 12:41 PM

Well.................. I said I was not all that experienced, but I thought I was at least basically intelligent.

After reading your replies I went back through everything I'd done and took a new reading in the sockets of the fixture. I can't recall if I did that again after replacing the switches (May have just asssumed thebiulb was OK as it was new). Whattaya know............... 120V!! So I checked the new bulb I'd just bought and it rattles.

The bulb is a 13W compact fluorescent with a square base and single contact prong on two sides. Not cheap!! I'll try to return it or just buy a new one.

I know the old bulb was bad too...... probably loose inside, as that would explain the intermittent working. This one is completely broken and I don't think it was the first tome I plugged it in, but I'll never know.

Will report back after trying a new bulb.............CAREFULLY.

I find it's usually something a lot simpler than what I think.

Thanks folks.

prj 02-17-2010 03:22 PM

OK. Now I'm getting really crazy.

I replaced the compact fluorescent with exactly the same type as was in there for years. When I flipped the switch the bulb began to glow yellowish near the base, got really bright (but only in that small base area), then went off. Now it will not light in any way.


AllanJ 02-17-2010 04:00 PM

Did you replace just the glass part with a small plastic snap in coupling or did you replace the entire assembly with the part that screws into the socket like an incandescent light bulb and weighs a little more?

prj 02-17-2010 04:27 PM

1 Attachment(s)
Here's an image of the bulb. There is nothing that screws in. It has a square center section and one prong on either side. The 'socket' is a square center female section with one contact female 'hole' on opposite sides.

joed 02-17-2010 05:21 PM

Bad ballast. That fixture has a ballast like the long tubes. The ones I have worked on were about 2 inch square and 3/4 inch thick.

prj 02-17-2010 06:49 PM

I can't see anything like that, so if that's the case, it must be in what I'm calling the junction box. I'll just have to see if I can feel around up there for a way to get at it. :mad:

AllanJ 02-17-2010 06:58 PM

So there is no intermediate component that screws into a round socket and, when removed, allows an incandescent light bulb to be substituted? That means the ballast is part of the fixture attached to the ceiling. With screw in CFL's the ballast is part of the light bulb and easily replaced.

With the ballast bad inside the fixture, you will probably have to replace the entire fixture.

It is possible for the contacts to be bad in the little holes that the pins on that bulb fit into but the fact the lamp (bulb) glowed brightly down at the bottom suggests those contacts are not at fault. Anyway it is very hard to restore springiness to that kind of contact.

There is still the possiblity that the bulb was defective out of the box. Bulbs of this kind have an element called the starter located inside the plastic base. If the starter is bad in a certain way then you get what you saw, the bottom part lighting up brightly. But if the starter is bad, consider the (entire) bulb bad.

Many older fixtures are torn out and replaced because no one wants to invest in a new bulb only to find that the fixture was at fault which fact was previously not known for sure.

joed 02-17-2010 08:45 PM

You need to pull the trim off from around where the lamp installs.
Here a picture of what it could look like.

prj 02-17-2010 09:20 PM

The 'fixture' is just a plain can with a round plate suspended in it that the 'receptacle' is attached to. two wires go from the back side of the receptacle to a hole in the can to whichis clipped a piece of bx cable. There's a box I can't see that's connected to the can by the piece of bx cable. I can feel it, but I can't see it unless my head will fit in the hole (which I doubt). I need to get my hand farther in there and see if I can loosen it or open it. It feels like a junction box, but it could be a ballast.

The saga will continue in the morning.

Again.................. thanks.

AndrewF 02-18-2010 09:55 AM

Can you take a photo where the bulb plugs in an post it here?

prj 02-18-2010 03:19 PM

1 Attachment(s)
This is where the bulb plugs in. Should there be a ballast up in the ceiling?

AllanJ 02-18-2010 04:00 PM

There is a ballast somewhere, maybe attached to the outside or the inside of the junction box.

Sometimes you can undo a few screws and lift out (drop out) the entire can and the junction box will then be easier to reach.

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