Strange 3-way Switch Problem

Little Bill

Little Bill

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Tennessee NEC:2017
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Semi-Retired Electrician
I saw this on another Forum. Thought it would be a good discussion here.
Problem was on a new house where one 3-way circuit wasn't working right.

Power in one box with 12-2
12-3 ran from 1st box to 2nd box, white as the neutral, red and black as travelers
12-2 from 2nd box to light, whites/neutral tied together all the way from box 1 to light
Light works, but switch at 1st box doesn't turn the light off
Switch at 2nd box turns the light on/off, like a single pole

Switches have been replaced and problem still exists
A piece of 12-2 was ran between boxes as a test, only replacing the travelers as the neutral is good because the light does work
With the jumper ran, both switches work like they should

Now, your thoughts as to what is wrong?
 
Call the ungrounded conductors at the two ends of the 12/3 R1, B1 at switch 1 and R2, B2 at switch 2. Presumably the 12/3 does not have the expected continuity of R1-R2 and B1-B2 with no other continuity, as replacing the travelers fixes the problem.

A failure of the form R1-B1-B2 all connected and R2 floating would explain the behavior. Or similarly R1-B1-R2 all connected, and B2 floating.

Cheers, Wayne
 
wwhitney said:
Call the ungrounded conductors at the two ends of the 12/3 R1, B1 at switch 1 and R2, B2 at switch 2. Presumably the 12/3 does not have the expected continuity of R1-R2 and B1-B2 with no other continuity, as replacing the travelers fixes the problem.

A failure of the form R1-B1-B2 all connected and R2 floating would explain the behavior. Or similarly R1-B1-R2 all connected, and B2 floating.

Cheers, Wayne
Click to expand...
Right…in other words, one of the travelers is open, plus they are shorted together on the switch 1 side of the open conductor.
 
Little Bill said:
I saw this on another Forum. Thought it would be a good discussion here.
Problem was on a new house where one 3-way circuit wasn't working right.

Power in one box with 12-2
12-3 ran from 1st box to 2nd box, white as the neutral, red and black as travelers
12-2 from 2nd box to light, whites/neutral tied together all the way from box 1 to light
Light works, but switch at 1st box doesn't turn the light off
Switch at 2nd box turns the light on/off, like a single pole

Switches have been replaced and problem still exists
A piece of 12-2 was ran between boxes as a test, only replacing the travelers as the neutral is good because the light does work
With the jumper ran, both switches work like they should

Now, your thoughts as to what is wrong?
Click to expand...
12/3 traveler is compromised? What does continuity check show on the travelers?
 
Little Bill said:
I saw this on another Forum. Thought it would be a good discussion here.
Problem was on a new house where one 3-way circuit wasn't working right.

Power in one box with 12-2
12-3 ran from 1st box to 2nd box, white as the neutral, red and black as travelers
12-2 from 2nd box to light, whites/neutral tied together all the way from box 1 to light
Light works, but switch at 1st box doesn't turn the light off
Switch at 2nd box turns the light on/off, like a single pole

Switches have been replaced and problem still exists
A piece of 12-2 was ran between boxes as a test, only replacing the travelers as the neutral is good because the light does work
With the jumper ran, both switches work like they should

Now, your thoughts as to what is wrong?
Click to expand...
Replace the installer, especially if he doesn't have a meter to easily figure out what is wrong. Sorry this is so basic I have very little tolerance.
 
retirede said:
Right…in other words, one of the travelers is open, plus they are shorted together on the switch 1 side of the open conductor.
Click to expand...
That's the theory. With flat XX-3 NM cable, the red is on one side, the white is in the center, and the black is on the other side. I'm trying to figure out how the cable could be damaged enough to sever one traveler, nick the other and short them, and not cause damage to the neutral and short it to the travelers.
 
Strathead said:
Replace the installer, especially if he doesn't have a meter to easily figure out what is wrong. Sorry this is so basic I have very little tolerance.
Click to expand...
The electrician that is troubleshooting it did not install the cable. His thinking is a screw, nail, or staple hit the cable. The HO did his own wiring.
He said the travelers had continuity. I can only guess that it maybe had enough continuity for the meter to read it, but not enough to carry current.
 
If the HO did his own wiring, that opens a whole can of worms. He could have a j box somewhere that he failed to mention, that he messed something up in.

As others have stated, the 2 tests are: pull the 3 way switch and check for proper functioning. I once wired a new house and out of the 12 3 ways I installed, 7 were non functional. They were Leviton. It was verifiable with a meter. Platt took them back. I was pissed to say the least.

Number two is ohm out the travelers.

Or 3, abandon the 12-3, pull a new one, hook it up and get paid. 👍
 
Seven-Delta-FortyOne said:
If the HO did his own wiring, that opens a whole can of worms. He could have a j box somewhere that he failed to mention, that he messed something up in.

As others have stated, the 2 tests are: pull the 3 way switch and check for proper functioning. I once wired a new house and out of the 12 3 ways I installed, 7 were non functional. They were Leviton. It was verifiable with a meter. Platt took them back. I was pissed to say the least.

Number two is ohm out the travelers.

Or 3, abandon the 12-3, pull a new one, hook it up and get paid. 👍
Click to expand...
The guy said he changed the switches.
He is replacing the cable. He said final inspection was coming up so he wanted to get it working.
 
Strathead said:
Replace the installer, especially if he doesn't have a meter to easily figure out what is wrong. Sorry this is so basic I have very little tolerance.
Click to expand...
Little Bill said:
.
He said the travelers had continuity. I can only guess that it maybe had enough continuity for the meter to read it, but not enough to carry current.
Click to expand...

I agree. Got a meter?? Know how to use it?? Know how to test a 3 way switch?? Know how to extend you meter leads with some ramen?? It's very simple: measure resistance on each conductor, and resistance between each conductor. Unless there is flux capacitor or non transverse quantum voltage transducer in a buried j box, the physics won't lie.
 
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