Thread: Hot Dimmer Switches

When a dimmer switch is hot (~110 F.), is this an indication of a bad switch or wiring issue?

I have been seeing this a lot lately in houses built in the 1990s. Not all switches are hot, but usually there may be one or two that are definitely warm to the touch.

Similar Threads:

• Bryant Light switches
• Switches
• Flashing lights on dimmer switches
• Emergency shut off switches.
• Dimmer switches

Depends on the wattage rating of the dimmer, any cooling plate or fins which may have been removed, and, most importantly - the number and wattage of the lamps (i.e., what is the total wattage drawn by the light fixture).

Dimmer get hot when loaded with wattage, dimmers get real hot when loaded with high wattage and / or cooling plates / fins have been removed.

Was the dimmer connected to lighting?
I have seen a general purpose rheostat used as a fan control.
Could have started a fire.


"Rheostats are made by winding nichrome wire around a round ceramic form. They have a knob adjustment that slides a carbon brush over the nichrome that adjusts the resistance. The Energy not diverted to the motor is then consumed by the rheostat and is dissipated as heat."

The larger the motor or energy requirement, the larger the rheostat needs to be.

Thanks for the feedback. To help clarify, these are wall mounted dimmers used to control recessed lighting. I cant imagine the owners removing any cooling fins or plates.

I have been writing these up as the standard ".....have evaluated by licensed electrician".

I would really like to know the root of the problem and how hot is too hot.

Originally Posted by imported_John Smith

I have been writing these up as the standard ".....have evaluated by licensed electrician".

Overkill in my opinion, unless maybe it complies with the answer to your next question.

I would really like to know the root of the problem and how hot is too hot.

Typically, the problem is overlamping (too many lamps or too high wattage for the dimmer rating).

It's too hot (in my opinion) if you get burned touching it, or even if you think you got burned. Children and some adults have more sensitive skin and 'could have been burned'. How hot is too hot in degrees F? I have no idea.

(added with edit: Actually, I do have an idea of how hot is too hot in degrees F, see attached.)

Originally Posted by imported_John Smith

I cant imagine the owners removing any cooling fins or plates.

John,

Happens frequently - some types of dimmers have breakoff tabs on both sides. If you gang two boxes side by side, you have to break off the tabs on the adjacent sides of both switches to get them to fit. If a control is between two others, you have to beak off both its tabs.

The instructions for such controls specify the derating for each tab removed, but few installers (electricians included, in my experience) bother to read the instructions, so it's easy to overload them.

That said the dimmers in the chart blow, installed in my living room and correctly derated, run at 110-115F (measured with an IR thermometer) under full load.

For future reference the Lutron Derating page is here:

Lutron Electronics, Inc.

John sez: "I have been writing these up as the standard ".....have evaluated by licensed electrician".

Jerry sez "Overkill in my opinion, unless maybe it complies with the answer to your next question(too many lamps or too high wattage for the dimmer rating)."

Jerry, when you mention overlamping, dont you think this is something that should be evaluated by a licensed electrician?

I really hate using the standard CYA cop outs, but if it doesnt seem right (such as 1 out of 10 dimmers is hot), I think its reasonable to recommend evaluation by an electrician.

Originally Posted by imported_John Smith

John sez: "I have been writing these up as the standard ".....have evaluated by licensed electrician".

Jerry sez "Overkill in my opinion, unless maybe it complies with the answer to your next question(too many lamps or too high wattage for the dimmer rating)."

Jerry, when you mention overlamping, dont you think this is something that should be evaluated by a licensed electrician?

Nope.
If it's real hot (see my temperature / burn chart), and you could get burned on it, yes, but look at those temperatures ... even at 140 degrees F it takes a little less than 5 seconds, and at 150 degrees F it takes about 1-1/2 seconds. When something is THAT HOT, you don't keep 'touching it' 'that long'. If you read 140 degrees F with your IR, yeah, go ahead and state that the dimmer is ' friggin' *HOT*, it's 150 degrees F *HOT*, if you touch it with your finger and do not almost immediately remove your finger - *YOU WILL GET BURNED*, have an electrical contractor verify that the dimmer is suitably rated for the wattage it is being used for '. You don't need to say 'have evaluated by an electrician', state what's wrong ( *IT'S FRIGGIN' HOT* ) and what needs to be done (have electrician verify the dimmer is properly rated for its current use).

If you just say 'have evaluated by electrician', the electrician may come in and try to make a fool of you 'Yep, that's a dimmer alright, and, yep, she's hot'.

When I would find hot water which was 'too hot', I would include that temperature / burn label I posted, why not include it when you find dimmers which are 'too hot'? That provides back up for your call ... "it's 170 degrees F as measured by an infrared thermometer - it says that at 170 degrees F - IF YOU TOUCH IT ... YOU WILL GET BURNED".

Originally Posted by Victor DaGraca

"Rheostats are made by winding nichrome wire around a round ceramic form. They have a knob adjustment that slides a carbon brush over the nichrome that adjusts the resistance. The Energy not diverted to the motor is then consumed by the rheostat and is dissipated as heat."

The larger the motor or energy requirement, the larger the rheostat needs to be.

I really doubt you will see anything this antiquated in residential lighting.

All residential dimmers have been using electronics for years. Study up on Thyristors, SCR's and Triacs. Warm/hot dimmers are very common and normal if the load is near the max and dimming is taking place.

Thats what I get from reading my antiquated ICC correspondence school "Principles of Electronics" material.
Shoulda known better.

Originally Posted by Bruce King

All residential dimmers have been using electronics for years.

As I recall, solid state dimmers came into 'regular residential use' around the mid 1960s. Before then, they were found in the higher end residences (due to the solid state dimmers costs, which came down in the mid 1960s, which lead to their common use). The first ones were all higher wattage ones with fins and cover plates which allowed air to circulate up through the fins, they took up about the same cover area as a two gang box.

Last month, I replaced two dimmers at a friend's home. Both were hot to the touch. Both were old. One dimmer replacement was necessary due to its age. The other was precautionary and we "de-lamped" the light fixture. There were ten 75-watt bulbs in the fixture. I teased her about wearing SPF-30 in that room.

No chart or electrical engineer was needed. Just less than $75.00 in parts and about an hour of my time.