I am primarily a teacher, and do some contracting work, but I will not touch anything electric (other than extension cords and lightbulbs) I do have a great electrician, and call him whenever I need help. (but could not get a hold of him tonight, hence the post…)
I was tutoring tonite, and the mother proudly was showing off her new kitchen, and the new granite backsplashes and switches. The switches had not been covered, and I noticed that the dimmer switch was giving off a ton of heat. I could touch it, and even hold it, but it was damn hot.
The mother said oh yes, the electricians said it is ok and when it is covered, it wont be that bad.
This seems to fly in the face of reason for me, but what do I know….
are hot switches a normal thing? it just doesnt seem right..
Replies
I have the same situation in my basement on a dimmer switch. If I hold a finger to the plate screws, they're hotter than hell. Called the electrician (very reputable) to inquire and he told me it's resistance heat and is normal, but if I wanted he could switch it out for a much larger appliance that would heat up to a lesser extent. Not satisfied with that answer, I called an inspector who confirmed the electricians claim. Now, I don't hold my finger to the screws (fast learner).
Carl
Dimmer switches do operate at higher temps because they are doing more work.That said,your dimmer switch is not going to be cooler when covered up,it will be able to dissipate less heat and be hotter behind the cover.They are rated by wattage so you should be able to add up the fixture wattages that are on the circuit and determine how close to maximum loading the switch is.It's bad to load these switches up too much (>80%)and it's bad to buy cheaper ones,they won't last.
Non-dimmer switches that are hot are often near the point of failure due to internal arcing.If a switch feels hot ,replace it.
jrobbins,
I'd be worried too. Dimmers have a heat sink, basically a metal flange with tabs all around the dimmer, towards the front, just under the plate. These tabs can be snapped off. If this is a multi-gang box, (more than one switch), someone may have snapped off tabs to make it fit, and destroyed it's heat dissipation capabilities.
Of greater concern is the possibility that someone has installed a 15 AMP switch on a 20 AMP circuit. Is this a lights only circuit? (As it should be) or are there outlets controlled by the same breaker? If there are, and a heavy draw appliance (say a microwave, or worse, a space heater) is downline of the dimmer, (that means further down the circuit, past the switch) there is a real risk of fire.
Also, if this was a remodel, it's possible that some genius decided that a 15 AMP circuit wasn't enough and took out the 15AMP breaker and put in a 20AMP without changing to the correct wire, switches or plugs. Again, there is a real risk of fire.
Was this job inspected?
I hope this helps, and I am not trying to over explain or talk down to you. You did say that you haven't much electrical experience. I have seen all of the situations which I have outlined and they all require immediate correction. As in turn OFF the circuit! Correct the problems.
Good Luck.
skipj
"I'd be worried too. Dimmers have a heat sink, basically a metal flange with tabs all around the dimmer, towards the front, just under the plate. These tabs can be snapped off. If this is a multi-gang box, (more than one switch), someone may have snapped off tabs to make it fit, and destroyed it's heat dissipation capabilities."
It does not destroy the heat dissipation capabilities, just reduces it.
Typically the flange with have the derating factors on it.
As mentioned the basic ones are typically 600 watts. With the tabs broken off on one side they might be raded at 520 watts and 440 with the tabs browken off on both sides.
"Of greater concern is the possibility that someone has installed a 15 AMP switch on a 20 AMP circuit. Is this a lights only circuit?"
As stated dimmer switches start at 600 watts (5 amps). The selection is based on the lighting load that is connected to it. It does not matter if the circuit is 15 or 20 amp.
Bill,
I take your points and will address them. I was trying to answer the concerns espressed by the originator of this thread without getting complex.
I didn't think that a long disgussion of the snap off flange derating would be helpful; calculating the line load quickly takes some experience. which he noted that he lacked. It's possible that the light circuit is overloaded.
RE: The Lighting load. If the downline cicuit load is wired in series through the dimmer (as opposed to a pig-tailed dimmer, which could draw into a 15AMP circuit with no harm) that entire downline load runs through the dimmer. The dimmer must then have the load capacity or will overheat, as this one has. Surely any warm electrical fixture alarms you?
Best,
skipj
I have a 2-gang box in my kitchen with two dimmers in it. One is loaded to 70%, the other to 30%. Together they are okay, even derated, but I wanted to help them out, so I installed a solid brass cover plate. The brass helps conduct the heat out to the room, and keeps the dimmers cooler. Looks nice, too.
Bugle
Edit: I forgot to reply to ALL.
Edited 5/14/2004 2:12 am ET by BUGLEHEAD
A little more background info, the homeowners tried to play general contractor to save money, and every time I showed up to tutor, something had gone wrong (pouring of the concrete/ running electrical lines/ inappropriate drainage) but I think they did hire a reputable electrician (who did not install cover plates on any of the outlets in a house with 4 kids) so I am not sure what is going on with the electric, the size of the breakers/wires.
I do also know that because I am such a chicken on all things electrical, that I might tend to exaggerate the severity of an issue (I came very close to electrocuting myself when I was 12 and that cured me)
Next time I am tutoring I will take a closer look at the switch and ask to see the breaker box
"I didn't think that a long disgussion of the snap off flange derating would be helpful; calculating the line load quickly takes some experience. which he noted that he lacked. It's possible that the light circuit is overloaded."
It is possible that the dimmer is OVERLOADED even with all the flanges intact.
It is possible that dimmer is NOT overloaded even with all of the flanges removed.
The only way to know is to check the load. Telling someone that it is "destroyed" by installing it the designed and specified maner is not helpfull.
Calculating the load on a dimmer is easy. Just count the total watts of the lights connected to it.
" The dimmer must then have the load capacity or will overheat, as this one has."
There is no indicate that this dimmer has OVERHEATED!
"Surely any warm electrical fixture alarms you?" No.
No, in fact it is common for many heat producting fixture to be warm. Feel any light fiture.
It does not ALARM me, but it might make we take a second look to see if the warmth is APPROPRIATE for the application.
Maybe there's some subtlety I'm missing here but re: the postings about the possibility of the dimmer wired in series with other devices... If that were the case, the dimmer would be "dimming" or varying the outlets or appliances "downstream". So unless your TV or dishwasher for instance is varying with the dimmer that's not an issue. Ummm as far as I know. And dimmers sure can get toasty under normal circumstances, I vividly remember running a light board in a small summer theatre as a kid and let me tell you it was hot as hell in that little room...
Paul
Old time theatrical dimmers are a whole different beast from what we use now. They were simple resistances in series with the load. So if you had a 10 kW dimmer half way up, you got an equal amount of heat to what was coming from the lamps.
Household dimmers are more sophisticated. They're duty cycle dimmers that work by using a triac that shuts itself off every time the AC sine wave goes thru zero. Then the triac is triggered on at some later time in the wave form. The heat in these is from the forward voltage drop across the semiconductor junctions in the triac. That times the current through the dimmer is the wattage that has to be dissipated. Figure 5 amps times a volt and a half, and maxed out you have 7.5 watts, about as much as a common Christmas light, for a 600 watt dimmer.
Virtually all the dimmers you'll see in retail stores are 600 watt, costing about $4 - $7. If you can find a 1000 watt dimmer, it'll be $40 - $60. (Had to get one for the dining room chandelier, 720 watts. Ouch.) Anything more, and you need a heat sink with fins on the wall instead of a plastic plate.
Breakers and other loads on the circuit have nothing to do with how much heat comes from the dimmer.
Any simple on-off switch that produces a detectable amount of heat is getting ready to crash and burn, so replace it ASAP.
-- J.S.
I realize that John, was just making a point about heat loss (resistive or otherwise)... I'll be more contexually precise next time ;)
I realize that John, was just making a point about heat loss (resistive or otherwise)... I'll be more contexually precise next time ;)
Don't be. We would have missed out on John's wonderful explanation of dimmers.
Standard home-duty dimmer switches are rated for 600W max. This means you can run six 100-watt bulbs or twelve 50-watters, or any other arithmetic combination that totals 600 watts. But as Barry said, maxing out one of these cheap dimmers is not a good idea. He gives a safe-use figure of 80%; I would be even more conservative and suggest 50%--a lot of these dimmers are manufactured overseas and quality control isn't what you'll get if you buy (and pay for) a Hubbell.
Lighting dimmers should never be used to control a motor, like a range hood exhaust fan or 'Casablanca' ceiling fan. There are motor controllers specifically made for that purpose--and they cost about 4 or 5 times more than an el-cheapo dimmer.
There is a quite noticeable amount of heat generated and given off by a dimmer in use, but it should not be hot enough to scare you unless you scare easily. It should under no circumstances ever get anywhere near as hot as a lightbulb, for instance. A description such as yours: 'Giving off a ton of heat'--well, that makes me wonder if all is right. I'd recommend buying a higher-wattage unit for that circuit.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
If the dimmer is not too hot to touch, and is not giving off an odor, then it is probably operating within specs.
j--
You've gotten some good advice from Bill H., Barry, and others who say that a dimmer can get quite warm and still be O.K., and that you could do a connected load calculation to see if the dimmer isn't overloaded.
On the other hand, this situation doesn't seem to present any undue hazard, and doesn't seem to be bothering either the homeowner or the electrician who did the installation. Then again, if you want to get involved in another "rescue" (in this case from an apparent non-hazard), have fun. I'd suggest that you encourage the homeowner to hire your electrician to offer a second opinion. My guess is that they won't, because they trust their electrician.
It's good that you asked the question, because there's no point in unnecessarily alarming a homeowner. It's generally a lot harder to calm someone down than to get them worked up about a situation--you know, someone says "this COULD cause a problem, danger!" when it's a non-issue. Then it's an uphill climb to put things in proper perspective.
Best regards,
Cliff
p.s. What do you teach/tutor? If it's science, you could turn this into a great opportunity to teach the kid some applied physics, electricity, and thermodynamics! CP
re: getting people worked up... My best friends are wonderfulllllll people, but can get rather ummm alarmist. One night I'm at their place for dinner, and he leans against the kitchen wall... "ouch, that's hot!". A spot immediately over a switchbox. I feel it, sure enough it's quite warm. His wife feels it, and says wow that's red hot! They tell me emphatically it's never been like that before, they'd have felt it when turning on the lights, etc etc... I'm trying to think about what's going on and reassure them that there's a reasonable explanation but the anxiety level rises very quickly. They're convinced there's a short within the wall etc etc. They ask me for some alternative explanation and while I'm pondering they approach hysterics "we have to cut the wall open and see what's happening in there..." No reasoning will work anymore so I take a Rotozip out of my truck and carefully cut through the plaster wall to find...
An uninsulated steam heat pipe...
Paul