Help me troubleshoot this weird problem

[Coppersmith]

Called out to fix a string of recessed lights on a three-way. One of the switches was a 3-way dimmer. Narrowed the problem down to the 3C NM cable. I took apart both ends except grounds. Red and black were the travelers. I assume the cable does not run through any j-boxes midway. I was told no-one had been in the attic (stepping on the cable) recently.

Continuity test showed red and black were shorted. (Lights were out. I would expect shorted travelers to keep lights on. Dimmer shouldn't care.)
When white was disconnected at both ends, there was no short to ground.
When the white was connected to the ground, a continuity test was successful.
When the white was connected to either the red or black, there was no continuity at the other end. (Weird huh?)

 

[retirede]

Did you check red to black at both ends? If not, it sounds like they could be cut as well as shorted.

 

[Coppersmith]

Did you check red to black at both ends? If not, it sounds like they could be cut as well as shorted.

Yes, shorted at both ends. It's acting like it's cut and both halves are shorted independently. That would be a one in a million shot, but possible.

 

[Barbqranch]

Any chance there is a 4 way switch in the middle you don't know about?

 

[retirede]

Yes, shorted at both ends. It's acting like it's cut and both halves are shorted independently. That would be a one in a million shot, but possible.

That’s exactly what is sounds like. Unless there something connected in between that we don’t know about.

 

[synchro]

Any chance there is a 4 way switch in the middle you don't know about?

If there was a 4-way in the middle and it was miswired, then in one switch position it could do exactly as was measured by shorting across each cable independently. And in the other 4-way switch position the travelers would pass through so that the two 3-ways would then work OK.

 

[LarryFine]

If there was a 4-way in the middle and it was miswired, then in one switch position it could do exactly as was measured by shorting across each cable independently. And in the other 4-way switch position the travelers would pass through so that the two 3-ways would then work OK.

To quote myself:

It's common to overlook that the two dark terminals go to one 3-way, and the two light ones to the other.

My dad replaced one once, and put the blacks on the dark terminals and the reds on the light terminals.

 

[Coppersmith]

Any chance there is a 4 way switch in the middle you don't know about?

I briefly looked for a 4-way and didn't see one. The area didn't seem big enough to require a 4-way. But a miswired 4-way switch makes the most sense. I'll see if I can determine if there is one there that I missed.

 

[James L]

I briefly looked for a 4-way and didn't see one. The area didn't seem big enough to require a 4-way. But a miswired 4-way switch makes the most sense. I'll see if I can determine if there is one there that I missed.

A bad 4-way could act the same as a mis-wired one.

I'm almost done with a new build residential that has Legrand Adorne devices. I've got one 4-way switch in the whole house and it's giving me fits. 2 bad switches in a row. The 3rd one just arrived yesterday so I'll go put it in this weekend

 

[synchro]

From what I see online, the Adorne 4-way has the black screws on opposite corners instead of on the same end (or side) of the switch. I guess if they're making the front side different then the back side has to be configured differently too?

 

[James L]

From what I see online, the Adorne 4-way has the black screws on opposite corners instead of on the same end (or side) of the switch. I guess if they're making the front side different then the back side has to be configured differently too?

They do.
Black screws diagonal corners and brass screws diagonal. Goofy, I tell ya

 

[James L]

Here's the Adorne 4-way

 

[synchro]

Here's the Adorne 4-way

There seems to be some inconsistency in the labeling of the terminals on this Adorne 4-way.

James L, just to make it easier to see this, I took the liberty of cropping your pictures and also rotating one of them 180° to highlight the IN and OUT locations. Also included is a diagram from the Adorne installation sheet.





As we know, the color of the screws for one pair of travelers (say the INs) is usually one color such as black, and the other pair (the OUTs) are another color, such as gold/brass.
The color of the screws in the pictures James L took are consistent with the IN and OUT locations shown on the installation sheet diagram. For example the black screws and also "IN" labels are across a diagonal. However, the labelling of INs and OUTs on the switch body in the picture don't seem to correspond to the screw colors or the installation diagram.

 

[James L]

There seems to be some inconsistency in the labeling of the terminals on this Adorne 4-way.

James L, just to make it easier to see this, I took the liberty of cropping your pictures and also rotating one of them 180° to highlight the IN and OUT locations. Also included is a diagram from the Adorne installation sheet.

View attachment 2555794

View attachment 2555795
View attachment 2555796
As we know, the color of the screws for one pair of travelers (say the INs) is usually one color such as black, and the other pair (the OUTs) are another color, such as gold/brass.
The color of the screws in the pictures James L took are consistent with the IN and OUT locations shown on the installation sheet diagram. For example the black screws and also "IN" labels are across a diagonal. However, the labelling of INs and OUTs on the switch body in the picture don't seem to correspond to the screw colors or the installation diagram.

I didn't even catch that.