Objectionable Currents vs. Electrical Interference

[Aaron Miller]

One of the many directions in which I can travel and fall off a tall precipice regarding electrical issues is interference with electronic equipment. Perhaps the resident doyens can lend me some direction.

The usual scenario is a light switch is operated and a noise is heard in the television or sound system that is in operation. This is a complaint I hear often from clients. I am out of my depth here but think I am close by referring to NEC 250.6(D) and 250.96(B). Would someone please volunteer to shed more light on the causes and possible corrections for these sorts of events?

[Rick Cantrell]

Replace the light switch, that may (should) stop the noise.
Likely the light switch contacts are corroded, or the light switch is a "Soft Switch"
Both can cause a spark (noise), which can affect electronics.

[Aaron Miller]

Replace the light switch, that may (should) stop the noise.
Likely the light switch contacts are corroded, or the light switch is a "Soft Switch"
Both can cause a spark (noise), which can affect electronics.

Rick: I am looking for a way to isolate circuits used solely or mostly for electronics so that one need not be concerned with faulty switches, et al.

[Rick Cantrell]

Rick: I am looking for a way to isolate circuits used solely or mostly for electronics so that one need not be concerned with faulty switches, et al.

You asked for causes and corrections. The light switch is most likely the cause and the correction is to replace it.
PS Most often this happens when the lights are switched OFF, but can happen when switched ON.

This is also common with cheaper electronic, (not properly shielded)
But can be on expensive equipment also (a lot of very complicated circuits)

Also you can check for ungrounded cable connections (spilters, adapters )
Cheap coax cable, or rolled up coax cable.

[Speedy Petey]

First off, this is not "Objectionable Current". It is simply interference.

Replacing the switch will probably help.

If you are looking to isolate the circuit then isolate the circuits. How this is done is not really a mystery. This is not a guaranty though that the issue will be resolved. Like lights dimming in a home when an A/C kicks on, sometimes it just is.

[Aaron Miller]

First off, this is not "Objectionable Current". It is simply interference.

Replacing the switch will probably help.

If you are looking to isolate the circuit then isolate the circuits. How this is done is not really a mystery. This is not a guaranty though that the issue will be resolved. Like lights dimming in a home when an A/C kicks on, sometimes it just is.

I never said it was an objectionable current.

[Kris Svendsen]

I'm not sure if this is the same type of issue that you guys are talking about, but I'll throw it into the mix anyway. I had a "hum" issue with a self powered sub-woofer that ended up being a ground-loop issue. My fix ended up being the use of a cheater plug on the sub (I know, I know..save the chastising so we don't hijack the OP's thread). I know you were talking about a light switch that caused a "noise", but even though it may not be the exact issue it may be similar enough.

Here is one of many articles about the "hum fix", if at all related to your issue.

Remove Subwoofer Hum (http://oreilly.com/pub/h/4241)

[Jim Robinson]

Since I remodeled my bathroom, when my exhaust fan timer shuts the fan off, I hear a very audible "click" in the stereo speakers in my office. The bathroom circuit is all new wiring, while the office circuit is 65 year old, non grounded wiring. The timer is a small electronic Leviton exhaust fan switch. Not sure what causes it, but it's not enough of an issue to make me interested in tracking it down.

[Speedy Petey]

I never said it was an objectionable current.Oh, OK. It's in the title.
Sorry 'bout that. :confused:

[Dwight Doane]

Rick: I am looking for a way to isolate circuits used solely or mostly for electronics so that one need not be concerned with faulty switches, et al.


First - make sure it is the switch - quick and cheap enough to find out [just try a simple on/off switch]

Second - are the AV and other communication wires close to the electrical wiring (they need to be an inch away from the electrical) (if they are too close the speaker wires could be picking up a signal like in a transformer) Also you may have a floating neutral in your office since there is no ground (seen it happen more than once) [this will often transmit signals too like radio stations]


Third - In my home all TV's and Computers have UPS/AVR systems (sad to say they are needed with today's electronics.

[Dana Bostick]

Any electrical current, when making or breaking contact, will produce RFI (radio frequency interference) all across the radio spectrum. 60 cycle current produces a 60 cycle hum that can be picked up by some equipment. Proper grounding and shielding of equipment can help.
Dimmers are the worst, usually the cheap rotary ones. The good Lutron sliders are better.

[Rich Goeken]

First - make sure it is the switch - quick and cheap enough to find out [just try a simple on/off switch]......
Second - are the AV and other communication wires close to the electrical wiring (they need to be an inch away from the electrical) (if they are too close the speaker wires could be picking up a signal like in a transformer) Also you may have a floating neutral in your office since there is no ground (seen it happen more than once) [this will often transmit signals too like radio stations].....

Actually good communications wiring practice calls for a minimum of 1' separation when running parallel to AC carrying cables, and should they need to cross them, do so at a 90 degree angle.

[bob smit]

My experience has taught me that the item/device/light etc is usually the culprit, although not necessarily in need of repair.
Properly shielded cable will render any remote RFI harmless as long as the shield is properly terminated and the equipment is powered by a grounded outlet.
Most RFI runs on the neutral/grounded conductor unless the item controlled by the switch is faulty.

[Aaron Miller]

Thanks for all of the comments. Let me know if I understand what I have heard so far. If I were to attempt to minimize or eliminate switch interference affecting electronic devices during the initial construction of a house I would:

1. Use properly-shielded cables for the electronics.
2. Install communications cabling a minimum of one foot away from current-carrying cables.
3. Only cross the two types of cables at 90° when necessary.
4. Use higher-end slider-type dimmer and fan speed control switches.

What about snap switch types? Which are least likely to become an interference problem?