[RFI] power line bypassing
jim at audiosystemsgroup.com
Sun Feb 13 16:26:22 PST 2011
On 2/12/2011 9:05 PM, Chuck wrote:
> A friend tells me he has an AC lines conducted noise problem from his
> next door neighbor's well pump. In the past, I have heard of people
> putting bypass caps onto their service entrance panel.Is his best answer
> to apply bypassing? If so, what is recommended?
You didn't say what frequency, or what the noise sounds like. The first
thing I would work on is making sure that the neutral and green wire are
not bonded together at the pump. Also make sure that no 120V motors are
running between one side of 240 and the green wire. Both are recipes
for noise. Also, try to figure out what kind of motor and motor
controller it is. If it is speed controlled, what kind of controller?
The best cure for most conducted noise is a good common mode choke, and
the most effective common mode chokes are formed by winding multiple
turns of the cable around the "right" ferrite core. The choke MUST be
very close to the noise source to be effective. Conducted noise is
really RADIATED noise -- the wire that conducts it becomes an antenna,
so the choke works by killing the current. You MIGHT do some good with
caps at the entry panel, but I suspect that the wiring that's doing the
damage is between the pump and the panel, in which case the caps
probably won't help.
For more, study http://audiosystemsgroup.com/RFI-Ham.pdf Also, study
the tutorial on Power And Grounding for Audio and Video Systems at
http://audiosystemsgroup.com/publish.htm While it's written for those
systems, the same laws and rules of good engineering apply, and the same
dumb electrical wiring mistakes cause problems at both audio and RF.
73, Jim Brown K9YC
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