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#164362 06/01/07 10:13 AM
Joined: Jul 2001
Posts: 311
We have a roof top air conditioner condenser 230 volts, 1ph, 28.9 RLA. When the unit starts a buzzing sound is heard in the conduit. There is no short circuit and the unit seems to run fine. What would cause the buzzing noise.

Joined: Jun 2006
Posts: 613
Current inrush sets up magnetic fields in the wires and you hear the wires moving in the raceways.

Joined: Jul 2001
Posts: 311
Would installing larger size conductors eliminate or reduce this effect?

Joined: Oct 2004
Posts: 806

No, but twisting or triplexing the conductors may help.

Check out THIS THREAD for some more info on the topic.

Joined: Feb 2002
Posts: 840
I have witnessed the same thing in two different situations. One was in a hotel electric room. The conduit feeding the elevator would literally make a "clink- clink" sound every time it operated. I amprobed the conductors and the amperage was going from 0 to almost 100 amps.

The other time was for a large pneumatic control system air compressor. The conduit was making more of a buzzing sound every time the compressor started.

My question is: Is this bad for the conductor insulation as the conductor moves around in the conduit?

Joined: Oct 2004
Posts: 806

Good guess would be that IF there are no burrs, rough spots or separated sections at couplings, it probably would not make a huge difference in insulation wear. Couductors will expand/contract slightly during normal use so.....

But then again, has anyone encountered any failures caused by the conductors shorting out or to the conduit, where it's possible that this rattling was the primary cause?

Iwire, togol, any such experience in your areas?

Joined: Sep 2005
Posts: 421
hear it all the time, maybe more with 1ph loads than 3 ph, but since conductors do vibrate with a load on them anyway, I don't concern myself with it unless the rattling is excessive
I do know that some of them have been in service for more the ten years with no problems.and I would suggest that any vibration problems show up at the terminations and not inside a pipe, unless somebody forgot to ream the ends , as you wrote

I have also seen raceways that had disintegrated long ago with the exposed wires still looped through a coupling, outside, in the weather just humming along

Joined: Feb 2007
Posts: 20
Junior Member
Would installing larger size conductors eliminate or reduce this effect?

I say YES.


What the hell do I know.

Joined: Aug 2004
Posts: 55
You might try a hard start kit for the compressor motor. Could save a lot of time and expense.

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