Why are dimmers de-rated for Halogens?

Question

Been fitting Halogen GU10 50w spots at a friends house over the weekend. Total 300w. Noticed as I went to fit the 400w dimmer I'd bought that it stated that if used with Halogen lights such as GU10's then max is 250w. Why is this? Now I've got to find a 500w dimmer (which supports 300w Halogen) in brushed chrome effect. Any ideas? MK have a white plastic one. May be able to drill out a chrome blanking plate to make the guts from the plastic one fit?

I assume if I did use the 400w dimmer it would run hot and have a short life?

Alan.

Dave Plowman (News) · Accepted Answer

The difficult part for a dimmer is the start current when the filaments are cold - their resistance is very much lower. And certain lamps of the same nominal wattage have a lower cold resistance than GLS types.

Christian McArdle · Answer

should handle the power. It looks like it would be easy to install ontoa blank faceplate.Christian.

Christian McArdle · Answer

Usually, although you often need to file out a little slot that engages witha keying protrusion on the pot.Christian.

Alan · Answer

Thanks Christian, they look ideal.I imagine with a hole drilled in the chome plate it should be an easy swap.Alan.

Dave Plowman (News) · Answer

You need also to check that no 'live' bits touch the metal plate. While itmay be a design that's also fitted to metal plates, I wouldn't count on it.

Alan · Answer

Good point, will do.

Why are dimmers de-rated for Halogens?

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