touch-sensitive switch malfunction

[prahadan]

I have a 2-gang touch-sensitive light switch installed in the bathroom. It has been working well for a few months, but today I switched the lights on causing one of the halogen bulbs to blow, and tripping the lighting circuit. I replaced the bulb and reset the circuit, but now the switch is constantly in the 'on' position. The other 'gang' works fine.

Can anyone enlighten me as to the way these switches function, and what could have gone wrong? Is there likely to be a separate fuse within the switch, or will I have to replace the switch?

Thanks, Dan.

 

[Spark123]

More than likely a triac has become damaged causing it to go short circuit. Unless you know someone into repairing this sort of stuff then the only other port of call will be to replace the switch.
Maybe it is just me, but it strikes me as a bit odd for one of these to be used in a bathroom, it is specifically marked as suitable for bathroom use?

 

[Adam_151]

In future try to buy the more expensive brands of lamps as these have an internal fuse that should opperate before the triac fails

It it indeed the triac that will have been damaged, when a lamp fails it often draws an arc right across the supply into the lamp which draws a lot of current (this is why some lamps trip B6 circuit breakers upon failing), and unfortunatly electronic components such as triacs are sensitive to this and triacs generally fail in the always on state, dimmer switches used to have fast acting fuses in once upon a time to protect them against this, but this seems to have been dropped as things become ever cheaper (still found in stage dimmers though - but of course they arn't a cheap commodity as are household dimmer switches)

If the dimmer was fused, it would of course fail in the off rather than the on state

 

[securespark]

Yep I concur. Lamp failure tends to toast switches of this ilk.

The older switches had miniature fuses in to protect the electronics, but modern ones don't.

MK, for one, put a warning in their dimmer boxes to fit fused lamps otherwise the dimmer will fail upon lamp failure.

 

[tim west]

In future try to buy the more expensive brands of lamps as these have an internal fuse that should opperate before the triac fails

Unless the fuse is semiconductor rated it's unlikely to be fast enough to protect the triac.

 

[plugwash]

maybe the answer is to fit an inline fuseholder in the backbox and fit it with an ultra rapid fuse.

 

[securespark]

In future try to buy the more expensive brands of lamps as these have an internal fuse that should opperate before the triac fails

Unless the fuse is semiconductor rated it's unlikely to be fast enough to protect the triac.

So why do MK specify fused lamps to be used with their dimmers then?

 

[prahadan]

Thanks for the responses. I've got a replacement switch, but I'm worried about the same thing happening everytime a bulbs blows. Any specific suggestions on inline fuseholders to include?

I was considering energy-saving halogens, though they are really expensive. Any opinioins on these? I'm guessing they should last long enough that I wouldn't have to worry too much about bulbs going.

 

[sm1thson]

Unless the fuse is semiconductor rated it's unlikely to be fast enough to protect the triac.

it is true that house fuses are slow to react, but you do get fast blow fuses and i suspect this is what would be / should be used

 

[tim west]

F rated fast blow is not the same rating as semiconductor rated or ultra fast blow fuses Ar rating etc

So why do MK specify fused lamps to be used with their dimmers then?

Dunno? Ask them