ECN Forum Forums General Topics of the Trade General Discussion Area Light Contactor humming.

n1ist "Also make sure the contactor is securely mounted in the box."


THIS is what I suspected but I wasn't sure! I waited to see if anybody else would bring this up. It could be coincidence but in one enclosure there are 6 identical contactors, as I said #5 was faulty.....the only difference I noted was that #5 was the only one secured by a single screw in the upper left corner. All the others were secured tightly by 2 screws at the upper left corner and bottom right corner.

I wondered if this had anything to do with the failure.

Sandro.


[This message has been edited by Sandro (edited 08-02-2003).]

Thinkgood I believe that is because for every cycle you cross 0 volts twice.

Bob

[This message has been edited by iwire (edited 08-02-2003).]

Many, if not most, contactors have copper eddy current rings wrapped around the ends of the pole piece. If those rings become loose, the contactor will buzz like a hive of angry bees. I've has some luck putting a little crimp on the side with a pair of dikes.

Thinkgood,

The industry usually calls it "60 cycle hum" because it is caused by 60hz power. The reality is that it is really 120hz (or 100hz for our friends across the pond) hum in transformers and coils, and flicker in fluorescent lighting.

The 120HZ hum is a result of the magnetizing current of the coil going to zero every time the voltage goes to zero. The voltage in a symetrical waveform crosses the zero axis 2 times every cycle.