Three way switch troubleshooting

[kwired]

Switch those conductors around so you are not switching the grounded conductor and you may still have some capacitively coupled voltage but it will most likely be much lower. Your digital meter probably reads some voltage just with one probe touching the ungrounded conductor and the other one in free air.

 

[gadfly56]

Switch those conductors around so you are not switching the grounded conductor and you may still have some capacitively coupled voltage but it will most likely be much lower. Your digital meter probably reads some voltage just with one probe touching the ungrounded conductor and the other one in free air.

Absolutely. I have an old Fluke 77, and I was showing my son how you could change the reading by moving the probe ends closer and further apart, both in free air. It would show 0.010 at 3" apart and about 0.020 5' apart.

 

[Sierrasparky]

Something is seriously wrong with that wiring schematic.
How can you switch the hot and the nuetral with the same switches.
Am I missing something.

 

[Pharon]

Something is seriously wrong with that wiring schematic.
How can you switch the hot and the nuetral with the same switches.
Am I missing something.

The neutral is switched in the first schematic and the hot is switched in the second. In both cases, it's a switch loop.

It might look confusing because of the colors of the conductors? I don't know.

 

[Sierrasparky]

The neutral is switched in the first schematic and the hot is switched in the second. In both cases, it's a switch loop.

It might look confusing because of the colors of the conductors? I don't know.

Looking at it again I see both switched

 

[Pharon]

Not sure how you're coming to that conclusion. Line power shows the hot as black and the neutral as magenta (white). Trace it out from there and the neutral is switched in the first schematic and the hot in the second. Unless I'm missing something.

 

[Ponchik]

According to post #12 the circuit at that point should work. Unless your drawing does not match the installed circuit and/or you have something else connected in series down stream.

 

[Pharon]

Update on this: I replaced both 3 way switches and when energized they work properly. Tested old SW1 and SW2 with an ohmmeter and SW1 did not ring out at all, which is strange. SW2 was fine. Both were wired correctly.

With the old switches still in place, I used a solonoid tester and it was a weak LED signal around the 12 volt range with both switches in the off position.

With the new switches in the off position, I'm still getting the same signal. So I think a different circuit is sharing this neutral somewhere. I'm going to try and trace it and see if there's a shared JB in the basement. If I can't find it, I'm just going to leave it as a switched neutral for now. I was planning on rewiring it anyway, but not for awhile.

Hell, it's been like this for over 50 years - another few months can wait.

 

[kwired]

Update on this: I replaced both 3 way switches and when energized they work properly. Tested old SW1 and SW2 with an ohmmeter and SW1 did not ring out at all, which is strange. SW2 was fine. Both were wired correctly.

With the old switches still in place, I used a solonoid tester and it was a weak LED signal around the 12 volt range with both switches in the off position.

With the new switches in the off position, I'm still getting the same signal. So I think a different circuit is sharing this neutral somewhere. I'm going to try and trace it and see if there's a shared JB in the basement. If I can't find it, I'm just going to leave it as a switched neutral for now. I was planning on rewiring it anyway, but not for awhile.

Hell, it's been like this for over 50 years - another few months can wait.

When switching the neutral nothing is "off" except the load itself.

Try removing all lamps in the switched load and I bet you get lower or even near zero readings, as the voltage potential from the ungrounded conductor is opened when the load is removed instead of passing through the load and being opened at the switch(es).

It was common to switch neutral in old wiring - especially knob and tube.

 

[Pharon]

When switching the neutral nothing is "off" except the load itself.

Agreed. And I recognize what kind of hazard that poses.

Try removing all lamps in the switched load and I bet you get lower or even near zero readings, as the voltage potential from the ungrounded conductor is opened when the load is removed instead of passing through the load and being opened at the switch(es).

Actually, when I took the readings, it was with the receptacle unconnected -- the readings were with open wires.

I'm still having trouble wrapping my head around it. With the 3-ways in the off position, voltage should be zero from the hot to the return neutral through the switches, right? I mean, it's an open circuit. How my solenoid is still reading a weak 12 volts, even with brand new switches is giving me a headache.

 

[kwired]

Agreed. And I recognize what kind of hazard that poses.


Actually, when I took the readings, it was with the receptacle unconnected -- the readings were with open wires.

I'm still having trouble wrapping my head around it. With the 3-ways in the off position, voltage should be zero from the hot to the return neutral through the switches, right? I mean, it's an open circuit. How my solenoid is still reading a weak 12 volts, even with brand new switches is giving me a headache.

When switching the neutral measuring from the "hot" to the return neutral should give you full 120 volts regardless of what position the switch is in.

If you switched the "hot" then you open the rest of the circuit from the "hot" when you open the switch or a portion of the circuit with a set of three ways.

Return neutral in either case is always at ground potential (disregarding a minor amount of voltage drop when the load is on).

Also be certain you don't have some "Chicago" or "California" three way setup, or it will really confuse you until you figure out that is what you have. In those setups they bring both the "hot" and "neutral" to the switch and connect to the "switched" terminals and connect the load to each "common terminal". Biggest problem with this code wise is it reverses polarity on the lampholder depending on switch positions, though it does work very well otherwise.

 

[Pharon]

When switching the neutral measuring from the "hot" to the return neutral should give you full 120 volts regardless of what position the switch is in.

Yeah, I misspoke on this -- when measuring from the hot to the return neutral that's been lifted, that's where I'm getting the weak 12 volts. In other words, not the neutral back to the panel -- but the white wire that comes from SW1 back to the receptacle box that's been lifted (from the 1st schematic).

Shouldn't that voltage be zero?

 

[FREEBALL]

I remember my first run in with a "California" threeway also called a farmers threeway you had hot on both ends so you could feed a recpt in a barn or whatever the travelers actually carried 120v so on either end you had 120v. Man took me a month of sundays to fig that out that was years ago. still like asking hot shots how this works lol

 

[kwired]

Yeah, I misspoke on this -- when measuring from the hot to the return neutral that's been lifted, that's where I'm getting the weak 12 volts. In other words, not the neutral back to the panel -- but the white wire that comes from SW1 back to the receptacle box that's been lifted (from the 1st schematic).

Shouldn't that voltage be zero?

That voltage is coming from "capacitive coupling". Place a load across it - even one with resistance in the thousands ohms range and you "short out" the "capacitor" and will not read any voltage. A low impedance meter provides low enough impedance to do this internally. Most standard digital meters have such a high impedance they do not "short" this weak "capacitor".