Dodgy dimmers

Tim M · 17 January 2007, 18:53

This is weird. In my sitting-room there are 8 ceiling lights - the flush fitted halogen sorts. Each bulb is 50w. I installed a dimmer just before christmas, and everything was fine. Then one of the bulbs blew. After that the dimmer wouldnt dim, the lights were either full on or off. I thought it must have been a dodgy dimmer so replaced it. That was last week. Last night another bulb blew, and the same thing happened - the dimmer wont dim.

Can anyone think why this keeps happening. The dimmer is suitably rated to handle this number of bulbs.

sparkey · 17 January 2007, 20:29

Are the lights mains powered (GU10) or via a transformer ie 12 V bulbs.
Most Dimmers must be derated when used on halogen downlighters.
Their rating is for standard bulbs only
Your load is 8 X 50 = 400 watts.
The very min size dimmer to use is 500 watt but for the sake of a few £££ more I would normally install a 1000 W dimmer unit. (same physical size).

Tim M · 17 January 2007, 20:55

Hi Sparkey.

Yes these are GU10. The dimmer is 50w overrated; I thought this would be enough. Doesn't sound like it is. I'll get a higher rated one tomrorow.

Just out of interest why would a bulb blowing cause the dimmer to blow?

Hightower · 17 January 2007, 21:38

I would guess that at the time of failing for a millisecond the amperage would spike and burn your dimmer out.