Remote/ touch Light dimmers - wattage question?

30 Jan 2007
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United Kingdom
I have been told by an electrician that if you use Gu10 halogen bulbs wired up to the mains, then you have to double up on the wattage of the remote dimmer switch. For example, if you have 4 x 50w lights then you to have a switch that can handle 400W (instead of 200w). Otherwise the lights will buzz and possibly flicker when dimmed, can someone tell me if this is correct? He mentioned something to do with "Inductive Loads" ???

If the above is true then my 2 x 8 50w lights would need a two gang remote dimmer capable of handling 800W each side. I guess there isn't such a product so I would have to have two single remote dimmer switches both at 800W each.

I have since been told by a supplier that if I was to use varlight remote switches then the above is not true (don't know what is special about the varlight dimmer ???), therefore I only need a dimmer that can handle 400w each side for the scenario above.

I am now confused and do not want to get the wattage wrong and buy the wrong products. Please could someone help??

Many Thanks in advance

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your electrician is right. hire him! :D lol.

Halogen loads are tougher on dimmers, and therefore it is always recommended (varilight or not) to de-rate dimmers.
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:rolleyes: No de-rating of dimmers is required for GU10 halogen lamps.

A mains GU10 lamp is the same type of load as regular tungsten lamp i.e. it's a resistive load consisting of a coil of tungsten in an inert gas connected to a mains supply.

This Chinese Whisper came about because when halogen lamps were first used in commercial light fittings they were only available in low voltage (being a spin off from the 12v halogen capsule first used in traffic lights). Being low voltage they required a transformer.

Early on only wire wound transformers were available and being an inductive load required a dimmer with higher capacity - typically the de-rating should be 20% so that's a 200va load on a 250 watt dimmer. But soft start dimmers need less de-rating.

Now electronic transformers are the norm and these represent a capacitive load and equally the dimmer should be de-rating by 30% so that's a 180va load on a 250 watt dimmer. But again better quality dimmers require less de-rating.

But if you have mains lamps you do not need to de-rate if you have 5 x 50w gu10 halogen lamps use a 250w dimmer :)
The coiled element of a quartz halogen lamp does have a huge inrush and as such they are a problem when used with electronic switching. It does of course depend on the design of the control as to how much spare capacity is required.

However the quartz is taken to a temperature which will cause it to reflect the active tungsten from it back to the filament and running cold will stop this process. So one should not dim a quartz lamp.

One of course can dim them, but it will reduce the life if you do.

Next is the type. The GU10 does present some inrush but one is unlikely to have compatibility problems using low voltage lamps. The extra low voltage lamps can be both better or worse. Some where the dimmer and inverter are matched can between them remove the problems of inrush. However if not matched then assorts of problems can arise even when the correct lead or lag matching has been done.

One has to by the same make of lamp, inverter and dimmer and if one blows likely it will take the other with it.

The same applies to GU10's in that when they blow often there is some ionisation and unless there is a semi-conductor fuse to protect the dimmer often the lamp blowing will take the dimmer with it. Just regard the dimmer as a fuse and be prepared to change it with the bulb.

With the withdraw of tungsten lamps I have removed all but one of my dimming switches and with the soft start slow warm up of the compact florescent really there is no longer a need for dimmer switches.

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