Cooked wall switch... Scary. Please come in...

[JeffKeryk]

My niece called me this morning with "a little question"; the hall light switch would not turn off the hall ceiling light. I called her daughter, who was home and I asked if it was warm or smelled. Not warm, but smelled "a little weird". I told her to flip breaker switches until the light went off and I would be over.

I pulled the cover plate; the fresh paint made a pretty good seal. Then the smell was strong! Now, I know my electrician limits and they are pretty low bar...
I cut the wires past the burn and simply put in the same switch to make it simple and hopefully safe.
My question is, what caused this? I guess the switch failed and/or was installed poorly because the light was on and the only wire damage I saw was at the switch. But again, my knowledge is minimal. Looks like the lower wire (to the ceiling light?) touched metal, perhaps?
Does my install look OK?
Any guidance is greatly appreciated. Thanks in advance.

 

[KGMtech]

Usually, this is because of loose connections on the switch. High resistance = heat generated.

 

[JeffKeryk]

Usually, this is because of loose connections on the switch. High resistance = heat generated.

Everything was tight.

 

[Pablo]

Looks like someone scabbed onto the hot side. Disconnect and see what does not work

 

[factorytuned2012]

is the switch grounded? that one wire that is not looped around the screw has poor contact area and is past the switch body it may have hit the yolk of the switch. why i say it may not be grounded is if it did the breaker would have tripped. your work looks okay just make sure you stripped enough and don't have wire insulation under the screws that also will cause a bad connection. fresh paint has someone had the trim plates off?

 

[NETWizz]

By chance was the wire damaged and rubbing making heat?

 

[JRay’07]

How many watts is the bulb that is being supplied by the switch rated for?

 

[pzev]

Does that switch control any outlets or are any outlets ran through that switch? I had a similar failure last year, the wall switch only controlled a ceiling light but a nearby outlet was still somehow wired through the switch as some kind of passthrough. I ran a space heater on that outlet and it melted the switch. It melted completely, looked like Chernobyl.

 

[Number_35]

That looks like there were three wires running to the switch - are they RD, BK, and WH?

If so, that's a 3-way switch.

I would expect a 4th wire, a bare copper ground, running to the switch's chassis.

 

[ripcord]

My mom told me that would happen if I kept flicking the switch on and off to watch the lights blink...

 

[Cujet]

Bad switch. This happens. Your repair will likely be just fine.

 

[factorytuned2012]

That looks like there were three wires running to the switch - are they RD, BK, and WH?

If so, that's a 3-way switch.

I would expect a 4th wire, a bare copper ground, running to the switch's chassis.

cant be a 3-way... 3 way switches dont have on and off

 

[Number_35]

Does that switch control any outlets or are any outlets ran through that switch? I had a similar failure last year, the wall switch only controlled a ceiling light but a nearby outlet was still somehow wired through the switch as some kind of passthrough. I ran a space heater on that outlet and it melted the switch. It melted completely, looked like Chernobyl.

Good thought about a possible excessive load elsewhere on that circuit.

You would expect the breaker to trip if the circuit was consistently overloaded, but some brands of breaker seem to tolerate excessive current without tripping.

The switch should have been rated for at least as much current as the conductor (presumably #14 AWG).

 

[Kira]

Everything was tight.

Yes, after the damage occurred. Meaning, you'll never know if it was loose beforehand.

 

[CarbonToast]

Amateur opinion is the wires not wrapped around the screws are causing a high resistance. Not enough surface area. The contact area the electricity is traveling across is just the tangent of the wire.

I would be inspecting every switch and outlet in the house after seeing that.

 

[eljefino]

Poor workmanship from the previous installer, you can see that bare copper (roasted red) is barely under the screw. You're supposed to bend into a 180 degree hook before torquing.

I would replace the switch as well in case it got compromised by the excessive heat. Edit, looks like you did, even though you wrote you put in "the same switch."

 

[Pablo]

Looks like someone scabbed onto the hot side. Disconnect and see what does not work

As I stated.........LOOKS like there two black wires. Is there? How did you connect the second wire to the NEW switch?

 

[mk378]

It was a stab in device. I can't see on the new one if it is stabbed in. A backwire switch is able to take two wires on the same screw (three if you also use the screw itself as well as the back slots). Backwire is different than stab in in that the wires are clamped by tightening the screw, not spring pressure.

Yes there is probably a heavier load downstream which caused the junction of the two hot wires to burn up. It is unusual for a light alone to do this.

 

[JeffKeryk]

There were 3 sets of wires in the box: 1 from the top and 1 from each side. I followed that. The 3 burned switch wires I cut and installed were all black.
The box ground wires were together but not on switch. The white wires were wire nutted together.

The top wire (hot?) was stabbed into the old switch; I installed it on the top screw of the new switch.
The wire on the lower screw (load?) was duplicated on the new switch. Supplies the hall light, right?
I stabbed the 3rd black wire in the hole in the back of the new switch, same as burnt switch. Not sure where it goes; downstream, right?

I guess if I had it to do over, I could have checked for the hot wire with the check tool. I feel bad about my wire hook installation... Pretty sloppy.

Thanks for all your help. Seriously grateful!

 

[JeffKeryk]

Poor workmanship from the previous installer, you can see that bare copper (roasted red) is barely under the screw. You're supposed to bend into a 180 degree hook before torquing.

I would replace the switch as well in case it got compromised by the excessive heat. Edit, looks like you did, even though you wrote you put in "the same switch."

Yes; I used a new switch. Took the burnt switch to HD to get the same style and ask questions. The worker was very helpful.

And I think you are spot on; the load wire was poorly installed.