On Sat, 4 Feb 2012 19:36:29 -0800, "walter"
wrote:

Ever since I installed a 7-station intercom system (hard-wired), 20 years
ago, I had an annoying buzz when I used the system in the evening, i.e. when
three kitchen fluorescent lights were on. The intercom does not buzz when
the lights are off. I am not referring the slight buzzing noise that comes
from the T-12 ballasts, I am referring to the induced buzzing in my
intercom.

How can I eliminate this type of 50-cycle interference? Can I put filter
capacitors in line with the ballasts? How about replacing the old T-12
ballasts with new electronic ballasts and T-8 fixtures? Would that help? I
believe modern ballast operate at a very high frequency. Maybe I should
connect the intercom master unit (also in the kitchen) to a different
electric circuit?

After 20 years, I am getting mighty tired of all this buzzing in the
evening. Of course, it only buzzes when I actually use the intercom to
answer the door or to suggest to my wife to fix dinner.

Thanks for any suggestions from those who have been there, done it.

Walter
My guess is you didn't use twisted pair wiring for the intercom.

Another possibility is switch polarity of the power wires and see
what happens.

New ballasts MIGHT help, but the electronic transformers on some low
voltage lighting also causes noise on intercoms and AM radios.