Blown Dimmer Switch

[fascha2]

I have a dimmer switch installed for the bathroom light at my cottage. The light fixture itself has 6 small 25W lightbulbs. For the past three years, the dimmer has worked perfectly. Three weeks ago the dimmer stopped dimming and could only be used to switch on and off. I replaced that dimmer with a similar (inexpensive) switch that worked quite well for three weeks - then the same thing happened - the switch was blown and would only turn off and on. This weekend I replaced the second blown dimmer with a more expensive ($20) dimmer. It worked long enough to show my wife how brilliant I was, and then stopped altogether. I replaced it with a normal switch for now.

I suspect two things - a short in the light fixture or a short in the wiring. On my next trip up to the cottage I plan to replace the light fixture with a simple fixture and install a (cheaper) dimmer to see if it the fixture that is causing the issue.

Any thoughts or advice on

1) what could cause the dimmer to fail after working fine for 3 years? 2) how will I be able to identify if there is a short in the light fixture (ie what do I look for)? 3) how can I determine if there is a short in the wiring?

Thanks!

[John Grabowski]

If there was a short the circuit breaker would have tripped. I've seen this happen before where a dimmer burns out for no apparent reason. Check to make sure all of your splices in the switch box and the light fixture are tight. I'm guessing that the light fixture has gotten a little old and the sockets are generating excessive heat and possible arcing. Might be time to replace it with a new one.

Is there any thing else on this circuit such as receptacles with a heavy duty appliance plugged in?

[fascha2]

Good to know about the breaker - it makes troubleshooting this a bit easier. I've checked the splices in the switch box and they are good. There are two outlets on the same circuit - one has a lamp plugged in and the other has nothing plugged in. I will check the connections in those boxes to make sure they are good as well. I suspect it is the light fixture - I will replace it this weekend and see what happens. Thanks for the reply!

[maradcliff]

Just so you know, they make the standard dimmers for 600 watt maximum, but they sell heavy duty or industrial ones in the 1000 and higher wattages.

Just curious, is this in a metal or a plastic box? Metal boxes help dissipate the heat from the dimmers faster. Heat is what kills them. Better to use a metal box, and always tighten the screws directly to the metal. DO NOT leave those little cardboard or plastic holders on the screws. A metal switch cover (plate) will also help cool them.

Mark

[Jeff Wisnia]

Any lightning strikes or possible power surges in your cottage's area?

You might want to consider installing a "whole house" surge arrestor across the incoming power line at the breaker box.

A 150 watt load isn't much for a dimmer like that, but perchance did a bulb burn out at the same time as the dimmer failed?

Bulbs can burn out with a "tungsten arc" effect which produces a very short high current spike which can fry solid state devices like dimmers. You can prevent that by wiring a 2 amp "fast blow" 3AG fuse in an inline fuseholder in series with the fixture. Then, if a bulb goes with a tungsten arc the 25 cent fuse will blow and save the dimmer.

HTH,

Jeff

[Chris Lewis]

According to John Grabowski :

A moderate-to-heavy short on the load side of a dimmer tends to fry the dimmer before the breaker has time to notice.

Silicon devices (eg: the triacs in dimmers) make _very_ _very_ fast fuses.

An momentary arc (bad lamp bases) might be the problem.

[RickR]

Quite right.

The dimmer is rated at 600W and the breaker at least 15A. Anything between these will fry the dimmer and not bother the breaker.

RickR

[fascha2]

This past weekend I replaced the light fixture and replaced the dimmer switch with a new dimmer. Everything has worked fine. I believe it must have been a short somehwere in the light fixture causing the issues. I appreciate the suggestions and the assistance.

[Art Todesco]

[Chris Lewis]

According to RickR :

And a heavy short in excess of 15A will fry the dimmer before the breaker notices. Breakers are very slow compared to the overheat time of a silicon junction.