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Question DetailsAsked on 4/26/2014

Dimming light switch gets warm.

Replaced switch with new, 1000W. (9) floods in kitchen - (5) floods are not dimming or dim-able. Old switch was not grounded. New switch doesn't matter grounded or not, still gets warm? Wire 12 ga, is not warm. This is a new house to us.

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2 Answers


Dimmers work by resistance and resistance creats heat. Unless your dimmer is extremely hot it is probably just doing its job. If the dimmer is rated for 1000W and you only have 100W bulbs in the 4 light connected to the dimmer 400W is not overloading it. I do believe the solid state dimmers do not get quite as warm so that might be an option. I am not an electrical engineer or even an electrical contractor but a general contractor so maybe one of those that are the help answer questions could step in to clarify as I have knowledge of most sytems in a building but not as detailed as they would be in this area.


Answered 6 years ago by ContractorDon


There are three common types of dimmers used in house circuits - you would have to google your manufacturer's website (or maybe Amazon) to find out which type yours is.

The switch should definitely be grounded - otherwise if it has an internal problem, it could become "live" and zap you.

The oldest type is a rheostat type like Don talked about. Like the volume control on a stereo or radio, it controls the voltage by increasing the resistance in the circuit - so basically it adds electrical resistance to the circuit the same as if you added more bulbs. This generates heat in the switch when it is in the dimming mode - the more you dim, the hotter it is going to get. Should never be too hot to touch, but many get to the "hot to the touch" stage where it would be uncomfortable to hold onto it. Many of these have box size restrictions, and shouldbnot be put in plastic electrical boxes. Generally, though it depends on manufacturer, they are supposed to have a 2-1/2x4 inch deep box for a stand-alone switch, or a 4x4 deep box if next to another switch, and you want to make sure the spare wire loops are not close against the back of the switch - I have seen burnt insulation in cases like that.

The second type is electronic and uses diodes to dim the lights - basically cutting the power on and off many times a second so the average voltage is lower, like a car alternator does as your battery charges, but is actually an average of on and off over time. These commonly get a little warm, but should not get "hot". Will typically burn out LED and CFL bulbs in no time.

The third type uses a transformer to reduce the voltage, and like all transformers gets warm because of the typically 5-15% efficiency loss in the transformer. Can get quite "warm" to the touch, but should not be "hot" - should be about like an electronic device charger or power supply heat range.

With any of the above, if it smells like hot plastic (except during the first 5 minute or so burn-in period when first used in dimmer mode), probably a problem.

Consider the type of bulbs too - some types of dimmers do not like some types of bulbs and vice versa - flourescents are generally not dimmable, CFL's only if they specifically say dimmable on them, and LED's supposedly are but shortens their life VERY dramatically, and I have seen and heard of both CFL's and LED's frying when on a dimmer or in-line photocell, so depends on brand and generally I recommend against either in dimmer use.

I am not clear on the 9 floods but 5 not dimming or dimable - are those on the same circuit and not dimming, or do you mean 4 are on new dimmer, and five on another switch ? If you have some dimming and some not on same circuit, then you likely have wiring problem in those non-dimming sockets - sounds like they are wired live and ground rather than live and neutral and the dimmer is on neutral rather than live wire, so they are not actually in the circuit with the dimmer switch. If that is the case, some rewiring in the boxes is called for.

You don't say what wattage the bulbs are, but from a practical standpoint your electrical circuit should always be 25% oversized for steady loads - so a 1000W dimmer switch should not have more than 800W of bulbs connected to it, for instance. Otherwise you can expect it to overheat,or at least get uncomofortably hot.

Answered 6 years ago by LCD

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