Landing light problem

[lubemonkey]

Hi,

My first post on DIYnot! Hope you can help.

I have a 12V landing light problem on the second floor of my 30's semi with loft conversion. A couple of nights ago there was a "bang" and the 2nd floor light circuit tripped out. Inspection showed one of the three landing bulbs had blown. Further inspection showed that the power lead into the transformer had been lying across the top of the fitment, had burnt through and shorted. I removed the offending article, untripped the circuit and I was then back to the two remaining lights working fine.

I replaced the transformer (burnt through supply wire too short to use again) and the bulb, and I had three landing lights working again. It was then that I noticed the switch for them on the landing below did nothing. On or off, upper switch on or off, no change.

So thought I'd inspect the inside of the switch in case that had somehow shorted/dirtied up. All looked and smelled ok inside, even the internal contacts of the actual switch. Put it back together and now none of the three lights comes on! I have unwired the lower switch and that has not made any difference - the upper switch does nothing.

The rest of the lights on that circuit are still working fine (bath/bed).

Does anyone know what might be happening here?

I have a multimeter at the ready......

Thanks in advance.

 

[riveralt]

Get your camera ready first and photograph the inside of the switch and the wiring at the lights - that will help trying to figure out what has gone wrong.

 

[bernardgreen]

When the short circuit occured the current through the switch was far in excess of what the contacts are designed to carry. This will have damaged the contacts. Most often they weld together and the mechanism is damaged. When you took it apart you almost certainly broke that weld.

You really need to replace that switch and maybe the other one as well as that one will also have had the excessive current flowing through it for the time it took for the MCB to trip.

In the Wiki you will find details how to change the switch.

I assume you have checked all lights to ensure there are no other cables in hot locations.

 

[lubemonkey]

Cheers for the responses chaps. Looks like you've sussed it Bernard - thanks!

I swapped the lower switch out for a spare and the landing lights are back in business. Upper switch seems ok.

p.s. as soon as I discovered the melted wiring I did a check on the other downlights. I must say that although none had damage, three out of twelve needed the transformer/wiring repositioning for extra peace of mind....