Smoke from a Dimmer Switch

[vwes59]

Got called out last week to some failed Kitchen Lights. They had a rather clever smart dimmer switch which usefully had a led light on it to say when it was working and connected to a smartphone. This was off, so I immediately suspected the switch as a point of failure, which it was.

Anyway, the 5 kitchen lights were 12V DC downlights connected to an unknown type of LED Driver in the ceiling void. They had a bought an identical light switch for me to install, so thinking this would be a quick change, I installed as per instructions, and hey presto everything worked....for about 5 minutes. I was just about to put everything together when smoke appeared from the back of the switch along with crackling and that usual smell of failing electronics.

So I made safe the wiring (which showed no signs of burning) and replaced it with a standard wall switch, which worked perfectly.

So my question is simply, what on earth went on here ? I've never had a dimmer switch burn out before, plenty of ones that cause leds to flicker, but this is a first.

I'm happy if someone could give me a technical answer to why this switch burnt out, and what I could do to solve the issue (if there is a solution or if they are stuck with non dimmable lights).

Thanks

 

[littlespark]

Was this smart switch replacing a regular 2 way?

I had a customer who had wired one up.... but the way it was wired, he sent 230v into a terminal designed for a elv signal from another smart switch.

 

[vwes59]

Yes it replaced a regular two way. So it had a line, and switched line to the back of the switch, no neutral.

My obvious thought is that either the driver is of a non-dimmable type or the LED's are or both, or the driver is totally of the wrong type for the load or any combination in between. What I don't understand is why the dimmer would quite literally burn out. Circuit is on a 6A MCB and RCD protected. Oh it burnt out when the LED's were at their maximum brightness.

 

[James]

Could there be other loads on light circuit after the suwitch? 500w flood by back door, extractor fan, kettle plugged into a socket for under cupboard lights?

Smoke suggests overloaded switch.
A 6A breaker will supply 1.5kw continuously, not many dimmer switches can cope with that.

 

[vwes59]

Just to update. When I investigated, I found a transformer that was not only a non-dimmable one, but not rated correctly for the lights. So currently the client has a standard 1-way switch, and we are discussing a way forward.