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Bradeno 02-03-2013 06:35 PM

Dimmer switch causing radio interference

I have dimmer switches in a living room and dining room.

In the living room there is a ceiling fan as well, however, the dining room chandelier is not yet up yet (haven't even bought it yet).

When I turn on the living room dimmer switch, it makes any radio I have on go to mostly all static. However, when I turn on the ceiling fan, a good portion of the static goes away. When I turn on the kitchen lights, it also lessens the interference (kitchen is located next to both the dining and kitchen rooms as it is an open concept floor-plan)

I was told confidently by one contractor that this is just a common thing with dimmer switches and there is nothing I can do about it, however, he often gives reasons for things he has little knowledge of to sound more competent than he is in every facet of construction (irritating because I sometimes fall for it and have to redo jobs).

I am thinking there is something wrong with a connection (a neutral or ground or something like that), but I don't know much about electrical other than remedial book work I did as an ME undergrad and some DIY repairs/installs. I was also thinking it might be due to the fact that I roughed in and nutted (but haven't yet installed to fixtures) wires for the chandelier.

Can someone please explain what the mechanism is that causes this interference exactly (I love theory) and how I might go about finding it and fixing it? Should I wait to diagnose it until after I have installed all of the lighting, or wouldn't that affect anything?

I guess I should also ask if this is a sign of something dangerous, just in case, since it involves electricity.


mikegp 02-04-2013 07:33 AM

The radio is plugged into a receptacle on the same circuit as the switch?

oh'mike 02-04-2013 07:49 AM

Not all dimmers are the same----the old style rotary dimmers in my house cause buzzing on the AM stations-----However the more modern (and more expensive) dimmers with the slide switch do not do that----

I'm not an electrician----one will be along soon to give you a real answer---:laughing:---Mike----

Bradeno 02-04-2013 10:14 AM

:) these are new switches.

Thanks for the response!

TarheelTerp 02-04-2013 10:45 AM


Originally Posted by Bradeno (Post 1108873)
I was told confidently by one contractor...
Can someone please explain what the mechanism is that causes this interference exactly

I am thinking there is something wrong with a connection...

Are you using halogen lights?

Oso954 02-04-2013 01:06 PM

Or worse, dimmable CFL's ?

Also, what make/model is your dimmer ?

dmxtothemax 02-04-2013 09:22 PM

Some dimmers produce more noise than others,
so a good quality is recommendded.
How ever if you live in an area where signal to noise ratio
is poor, then even good quality ones can cause problems.
with dimmers noise is radiated from not only the dimmer itself,
but also the cables between the dimmer and light.
Putting the wiring into metal conduit and grounding the conduit
will usually help.

Bradeno 02-05-2013 07:23 AM

The dimmers were only installed last year, and I don't want to crawl up into the attic again and run conduit on all of that wiring. Ick. :) They are the switches with the dimmer-slide along side them.

They actually are CFLs. You think that is the problem? Why does that cause any more interference than other lights? They are getting rid of incandescent bulbs soon, aren't they? What then?

Also, why does the ceiling fan or kitchen lights being in use mitigate/cancel out the interference? Anyone know the mechanism of what is going on?

Oso954 02-05-2013 12:54 PM

Yes, cfl's are often a source of RFI. The CFL's have electronics in the base of them. When you dim them, it can exacerbate the problem. (The dimmer can also be an RFI source) While the Bulb Mfg. says ordinary dimmers will work, CFL dimmers tend to work better.
(LED's can also be an RFI source, but tend to be less problematic)

While the pure incandescent light is going away, Halogen replacement bulbs are already on the market. The 100 watt bulb is replaced by a 72watt. (28% more efficient).

I think you are dealing with RFI on the wiring, not RFI being transmitted like a radio signal. But you could have both. One way to test this would be to bring a battery powered radio (tuned to the same station) into the room. Does it have interference ?

I would try putting incandescents in to see if that clears up the problem. If it does, I would then try the halogen replacements. For a test you can just use a couple of bulbs, but all the CFL's must be removed.

Bradeno 02-05-2013 06:18 PM

There are 4 CFLs on the dimmer switch in a square pattern. In the center of that square is the ceiling fan which also has 4 lights. Why would turning on the ceiling fan cancel out the interference created, by the CFL transformers or the wiring or whatever it is?

dmxtothemax 02-07-2013 04:42 AM

Changing the load, changes the nature of the load,
this alters the tuning, thus altering the resonance.
resonance and rf circuits are very complex,
it would take a very long time to explain it in detail.
but it can make a substancial difference.

kevinb70 02-07-2013 05:01 PM

The coils in the fan are acting as a choke coil which eliminates the electrical noise caused by the dimmer/CFLs.

Note: there are regular CFL bulbs and then there are DIMMABLE CFL bulbs. The Dimmable ones cost a lot more than standard CFLs.

Standard CFLs do a horrid job at dimming. Noisy, huh? Expect them to burn out faster too.

There are standard dimmer switches and then there are (expensive) dimmers just for CFL and LED bulbs.

I would NOT use a CFL bulb with a dimmer. They just won't ever work right and do not have the dimming range of a incandescent bulb.

I would
A) go back to dimming incandescent bulbs and forget CFLs in this fixture. CHEAP!
B) replace the dimmer switch for normal on/off switch. CHEAP!
C) buy a CFL/LED dimmer switch and replace existing dimmer switch AND replace standard CFL bulbs with DIMMABLE CFL bulbs - EXPENSIVE all around!
D) buy a CFL/LED dimmer and replace existing dimmer switch AND replace standard CFL bulbs with LED bulbs. EXPENSIVE.

I'd never go with option C... dimming CFLs is akin to bashing one's head against a wall. With CFL warmup and inability to have a wide range of dimming, and at lower levels the CFL will just cut off... too many headaches with dimming CFLs. CFLs with on/off switch only!

Also with previously mentioned - try halogen. To avoid decreasing life of halogens attached to a dimmer, you'll need to periodically run them at 100%... which you'll probably forget to do .... so I'd opt for removing dimmer switch or just switching back to incandescent bulbs.

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