18 year old house. Flipped the switch, and sparks/flames shot out from the gaps in the cover plate. Breaker tripped, but still works. When a switch fails, could it cause the cracks shown in the photos? Or, could this switch maybe been installed irresponsibly with existing cracks? (Not shown in photos, but yes, there is a grounding wire. That is soot near the green ground wire screw.)

 

There are some switches that are made as cheaply as humanly possible. With that, the type of plastic used is prone to cracking and breaking, even moreso after a few years of use.

IMO, the short/arc happened when you toggled the switch. Something finally gave way and shorted or arced.

I'd recommend upgrading to $2-4 switches instead of the $0.75 devices that are currently installed.

 

What was the switch operating?

I suspect the cracks happened when the short happened. That is what caused the spark, flash, and soot.

You have (or had) a short on the load side (downstream) of the switch. When you flipped the switch, that closed the contacts inside the switch, and current was allowed to flow freely until the circuit breaker tripped. I suspect the switch is toast.

You will need to be VERY careful if you replace the switch because the short may still be in the circuit and the same thing could happen. Sometimes a short will burn itself open and the fault will clear. Then when the switch is replaced all that happens is that part of the circuit will not work anymore.

 

The switch was operating the light kit (3 bulbs) under a ceiling fan. Probably the original fan/light from the builder, 18 years ago. Separate switch for the fan motor.

Q: Is a short in the circuit more likely than a failure within the switch itself? (Wishful thinking on my part.)

I would expect a downstream short in the circuit to trip the 15A breaker without frying a 15A switch. (Expecting the switch to have some additional current capability above 15 A.)

I would expect a short failure in the switch to create sparking as a new unconventional electrical path is formed. Tripping the 15 A breaker.

By the way, I inspected the neighboring switch (for the ceiling fan) and see that a corner is flaked off where one wire hole is. See photo. It is a three switch electrical box. I suspect that this issue was cause by the stiff wire pushing against the relatively weak plastic corner of the switch. Bad luck? Or did the electrician installing these stress the switch by cramming too much extra wire/cable into the box? I picture new build workmen doing repetitive work in a hurry, and not being as caring as a homeowner doing a single repair job.

 

Weird.... rarely see one cracked switch and you had two.
The one that burned was broken around the black wire.

Turn the breaker off.
Temporarily connect the two wires with a wire nut and turn the breaker back on.
If the lights work... the circuit should be ok. Replace the switch.

 

I have used to say that the US Toggle switches is far more reliable than what we use here in Norway after 1950. Not that convinced anymore, but if you use far to much tension on the screw terminals will it split up further?
Could that have been the reason ?

The pretty large move of the switching parts make the risk of arks smaller.

 

When you replace the switches do not use the stab-in openings in the back--use the screw terminals. Stab-in connections are prone to overheating and may have added to the structural failure of those switch housings.

 

If the short happens when the switch is off then the arc flash would occur where the circuit is closed, at the switch. Example: A person wires a light fixture with the switch off, but the hot wire comes undone and touches something grounded. The short is present but nothing happens as the switch is off. When the switch is turned on the arc happens at the switch because that is the final point of the circuit being closed.

I suspect defective material. The wire would normally bend before the would plastic break. I also recommend replacing both switches.

 

I've never seen a switch crack like that, what brand was it?

 

I do not see a manufacturer name anywhere on the switch. Builder probably bought these by the thousands. And the electrician used the stab in connection holes to save time.

I replaced both with the better models from HD. So, not the 75-cent ones.

Thanks for the responses.

 

So everything works again?