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I have two dimmer switches that have started malfunctioning. They are in the same box with two other standard switches. Each controls a set of three small flood lights. There is no other way to control these floods except with the dimmer switch. They were working fine last week. Now, when I slide the dimmer, it sometimes works and sometimes doesn't. I know it isn't a circuit breaker problem since the other switches are on it as well and they work. These were installed about 6 years ago. I will need to call an electrician to fix this but would like to have an idea, if possible, of what the problem could be.

  • When it "sometimes doesn't" work, do the lights come on at all? – K.A Jan 5 '14 at 2:48
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    In my experience, dimmers seem to fail relatively frequently compared to switches. – Steven Jan 5 '14 at 2:51
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    I don’t know which type of construction you have, but if the sliding part is attached to some variable resistor, that may simply be dirty and/or worn out. It will probably be more economical to get new ones than to pay an electrician to take one apart and clean this place, though – even if that would be slightly cheaper, the problem will resurface, probably sooner than with a new one. – Christopher Creutzig Jan 5 '14 at 14:35
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    Dimmers have maximum ratings (usually 300 watts or 600 watts). If you exceed the max, they may burn out. Also if they are mounted next to each other, part of the heat sink face plate is usually trimmed off, reducing their wattage max. – bib Jan 5 '14 at 21:05
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    Thanks for your replies. I don't trust myself to do anything electrical. I will call my electrician to check it out and replace them. – user19119 Jan 9 '14 at 19:03
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Sounds like a simple case of a bad switch.

Note: a squirt of WD-40 into the right place in the sliding mechanism can help, or even fix the problem at least temporarily by lubricating the internal sliding electrical contacts. But getting the location right requires experience, and if you have to bring out an electrician anyway, they'll prefer to replace.

Do this with the power off by the way. And it's far better to take it apart and lubricate, compared to the squirt and hope method.

Consider upgrading to a dimmer model with a remote control, CFL compatibility, or other features.

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    WD-40 is flammable. Spraying it into a light switch is probably not a good idea. – Andrew Medico Jun 9 '14 at 20:00
  • With the power OFF. – Bryce Jun 11 '14 at 3:36
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    WD-40 is bad for plastic, use contact cleaner if you must. – Mazura Aug 19 '14 at 1:46
  • True, I have wrecked dot-matrix printers by wetting dried-out ribbons with WD-40. – Harper Mar 11 '16 at 21:15
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Your dimmer was probably damaged by excessive heat and maybe more load than it is rated for. Solution:replace bad dimmer with one that is rated at or above the amount of watts you are controlling with it if one dimmer is a 3 way you may be able to put that one on the other end and a regular 3 way switch at that box. Otherwise you may be able to change your lamps to dimmable led s that will reduce the load and also the heat. But still replace the dimmer they are not repairable.

  • Can you point to the section in the National Electrical Code that prohibits multiple dimmers in a single box? – Tester101 Aug 8 '14 at 15:40
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    I'm not aware of anything prohibiting it. Most dimmers have heat sink fins that can be snapped off for higher density installs, however every fin that is snapped off reduces the wattage rating of the dimmer per the manufactures specs. So it really has more to do with load on the dimmers then the number of dimmers in a box. – Steven Aug 8 '14 at 17:34
  • Sorry I knew I had read that somewhere it must have been in the manufacturer's instructions for a dimmer that I have used in the past . one that I was just looking at describes a reduction in wattage per number of dimmers ganged. – user24125 Aug 9 '14 at 0:45
  • No sense in asking for a code reference because it does not exist. As Steven says, it is clearly explained in the instructions how to break off the fins if dimmers are to be ganged. – Speedy Petey Aug 10 '14 at 12:08

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