Overheating transformers?

[mr_small]

I've referred to this site plenty of times, but now somethings happenned and I need help! I have recessed halogen downlighters upstairs. Each light has its own transformer. I put insulation in the loft last week, leaving what I thought was sufficient space around each fitting/transformer to prevent overheating. I had the lights on for several hours tonight, and when I went upstairs later on one of the bedrooms lights were all out. The other room was OK, and the rcd circuit which serves both rooms had not tripped. Could it be the dimmer switch serving the room that has overheated, or could one overheated transformer take out all the other lights in the loop? The thing that confuses me is that the other room is OK, even though it is on the same circuit. Any help or advice would be greatly appreciated

 

[Steve]

How much space is around each fitting before insulation? Its not clear if just one light has gone, or if the lights in one room have all gone. What rating is the dimmer switch in question? What rating of halogen lights does it switch? One overheated transformer shouldn't take out the rest unless it trips the circuit breaker while overheating and cutting out.

By the way, you sure that's an RCD? i'll bet its really an MCB, being a lighting circuit and all (clue: RCDs have a "test" button and usually say "test frequently" on them, and a little diagram of their innards)

 

[mr_small]

I went to bed after writing last night and suddenly thought - doh! I meant MCB, you are absolutely right. I laid insulation between the joists, leaving a hole in the insulation typically 20 - 30cm diameter above each fitting, then re fitted the boards, and then put more insulation on top of the boards (cold house!). I did not take account of the location of the light fittings when putting the 2nd layer of insulation on, as I thought I had left plenty airspace below the boards. I laid the insulation under the wiring before refitting the boards.

All of the light fittings in the room (5 x 50W halogen) stopped working, but the en-suite lights and adjacent bedroom lights, all of which are on the same circuit, work just fine.

I dont know the rating of the switch - just moved in last month and the work was all done by the previous owner last year. Its one of those flush fitting stainless steel switches. How would I establish the rating? I thought of swapping the switch tonight just to see if that was the fault.

 

[Steve]

take the switch off and look on the back of it. Having 250w of halogen means you need a 500w dimmer switch (in general, dimmers can only switch half their rating when used with halogens). Swap the switch for a normal one and see it if works then.

As for the insulation, this is unlikely to be your problem - you left sufficient space, but no provision (as far as i can tell) to ensure the insulation stays away from the lamps. Nevertheless it should be okay as you only laid it a week ago! Consider the switch before you worry about the insulation.