3 way switch weirdness

[Malamute]

A friend had a ceiling light that stopped working. Basic multi-meter showed both 3 way switches had power and it alternated which terminal when they were switched. OK... Check power at ceiling box, 120v, switches seem to work fine with alternating on-off and both switches activated alternately. Track light doesnt work. Has 120v at the button that twists into the track, but the light wont work, new bulb....tried same light in another track, it worked. She got a new track, it wont work.....after some puzzlement, I kept the meter on the track when switching the actual track fixture on, the 120v goes to 10v and no light. What the WTF?

Is it a weird switch issue/failure? Just replace both switches and drive on?

ive seen them fail by not passing power through, and only one working, but both seemed OK when using the basic analog meter, never seen one fail with a load but otherwise appearing OK.

Ive disassembled the actual spot type fixtures, nothing seemed wrong, the manual switch worked fine, all contacts seemed intact and properly arranged.

[rdtompki]

loose wirenut/connection on return would be my guess.

[Malamute]

Thanks, that had occurred to me, but will have to wait until I can go back over.

[tadawson]

If you can meter across segments, switches, etc. you can get a better idea where the fault lies by finding the point where voltage is lost and should not be. IE, if the light is mounted to a grounded box, try reading hot to neutral as well as hot to ground. As noted, since you say that position does not matter, this fault is clearly on a single wire segment, and could still be a swich, since I think they use a single contact to connect to either pole.

(Myself, I'd check the switches *first*, since they are the only non-passive devices involved. Short of rodents, wire rarely just fails sitting there undisturbed.)

[Malamute]

I checked the fixture at both ground at box (obviously wired to ground wire) and neutral, same result.

I didnt check the switches under load, just that they were passing 120v and seemed to operate normally before going dowstream to the fixture. I told her to get 2 new switches, in the interest of time.

Ive seen breakers get sort of weird, half of a main 220 breaker fail (half the house works the other half doesnt, or not at full power), and even brand new GFCI outlets fail right out of the box, just not seen a switch fail in a load situation. Not saying its not possible, just puzzled me, hence asking if its possible. Some electrical things have voodoo or something going on.

[Wheeler]

Is this ceiling fan and track light on the same set of 3-way switches? Sounds like you've lost a neutral somewhere, probably a bad tap or burnt up wire nut. I'd check the taps in the box supporting the fan, those are usually a failure point, especially in the older ones that didn't have support hooks to hold the motor while wiring.

[whomever]

"I kept the meter on the track when switching the actual track fixture on, the 120v goes to 10v and no light"

Dunno if this is your problem, but when you have two wires running parallel with one energized and the other not, the energized one will induce a potential on the non-energized one. You can see, say 90V, but it's at negligible amps if you connect a load, so connecting any load drops the voltage a lot.

3 way switches are prone to exhibiting this when run with 3 conductor romex, for example. I usually see maybe 80V dropping to 0 on load, but those values probably depend on the lengths involved etc.

Not an EE, may have garbled the explanation, just scratched my head over it the first time I encountered it and asked a cluefull friend.

[Caballoflaco]

I have seen some of the bad Chinese sheet rock cause corrosion where wires were connected into switches and outlets. However, if that’s the case here you should pretty easily be able to see verdigras and corrosion on any exposed copper or brass.

We had to strip back all the wiring to clean copper and replace all of the affected switches and outlets.

[Malamute]

Is this ceiling fan and track light on the same set of 3-way switches? Sounds like you've lost a neutral somewhere, probably a bad tap or burnt up wire nut. I'd check the taps in the box supporting the fan, those are usually a failure point, especially in the older ones that didn't have support hooks to hold the motor while wiring.

No fan, just the single ceiling box with a track light on it.

Ill have to look in the switch boxes again, I was mainly looking to see if the switches had power and seemed to be functioning normally, which they did, and power was getting to the ceiling box, so I closed them back up.


Yes, ive seen a number of ceiling fans set on non-fan rated boxes.

[UNK]

If I suspect a switch I hold a screwdriver by the the shank and tap the toggle with the rubber coated handle.