OK, as professionals, we know that you aren't supposed to use a dimmer on a fluorescent lamp. Problem is, that the general public does not know this. With CFLs being all the rage, it's just a matter of time before we start seeing more and more stories like this:
I have to wonder quite how this could happen, and if it indicates a basic design shortfall in the item involved. There is no indication whether the dimmer or the lamp was the source of ignition, but in either case a safe failure mode should have been designed in. (eg thermal fuse) After all, if the device has the ability to overheat to ignition point there could be other faults leading to this, without someone mixing incompatible items.
Geoff, I believe harmonics are to blame. The dimmers are designed to power simple resistive loads and contain transistors that switch on and off very rapidly to dim the lights. The CFLs, on the other hand, contain capacitors which are designed to operate at 60Hz, but are now subjected to much higher frequencies, at which they offer a far lower resistance- essentially becoming a short circuit to ground. These components are super-cheaply designed already, but with the dimmer, they overheat and blow even quicker. The extra current through the dimmer would cause it to overheat quickly, too. A thermal fuse would help immensely in the dimmer, but I don't believe it would do much good in a CFL. Better solution would be an inductor designed to trap the higher frequency harmonics. But this might only give the illusion of being able to work on a dimmer, and still cause problems.
Honestly, consumers have every warning- it's clearly labeled on the CFL package, and clearly labeled on the dimmer package, and 99.9999% of the time, the CFLs just die quickly with no fire, and the consumer learns his/her lesson, and spreads the word to their friends. The Darwin awards exist for a reason.
I agree. I've put in thousands of panels and GFIs and assure you that I've never read the instructions or warnings. The sad thing is that I just realized that in my own bedroom, we have CFLs in both lamps since they have flimsy paper shades. I did this because I was afraid that the heat of a standard "A" bulb would scorch the shades. One of the three switches in my 4-way setup is a dimmer! We never dim them, but I honestly never even thought about it. I sure will now.
All the labeling in the world may reduce but not fix it. As electricians, do we read the packaging and the safety warnings before installing something?
Good point, This is why it is important for electricians to keep up with the latest and greatest.
There are fish-hooks in installing any new item to the market in somebodies house, etc.
I had an instance of these CFL's nearly catching fire a few years back in the house next door to where I was living at the time, but these weren't on a dimmer.
Just on the subject of dimmers vs CFL's, I recently installed some CFL's for a guy down the road, I told him that I would have to remove the dimmers from his lounge lighting circuits, because the two do not agree with each other. The guy could not seriously believe that you could not dim a fluorescent lamp! (I realise that they can be dimmed, but the control gear price is really only for Commercial installations)
#177443 - 05/02/0807:43 PMRe: CFL controlled by a dimmer causes house fire
There are a number of CFLs that are advertised and marketed as being useable with dimmers. As they are relatively expensive ($15 each) and I don't have any dimmers in my house, I haven't tried any of them.