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Hackenschmidt
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Check HZ the same way you test for voltage, only on the HZ setting.
Most people do Phase to ground.
I did not know you could see that with a meter, I thought you'd have to use an oscilloscope.
No, I would of never thought of that. How the heck to you check hertz?
Poor man's alternative. Someone correct me if this is wrong. Measure the neutral current with an average-responding meter (that is, just a regular less expensive non-true-RMS meter) then measure again with a TrueRMS meter. If the current is different, it's likely due to presence of harmonics. (Of course you still would not know the frequency of the harmonics.)
 

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You aren’t going to read anything of note measuring the frequency of the cycles. You’ll likely get anywhere from 58-61, if you drop frequency of the cycle more than that you are in deep. By the time you’d notice that kind of drop your grid will probably drop. Frequency drop is a sign of generating source lagging the source will shut down before any damage occurs. If there was a stray rf signal to measure you’d need to use a spectrum analyzer/service monitor to get anywhere. Try shutting off different types of equipment. Banks of similar types of lights, electric heating, motor loads, try shutting sections of the panel off, listening for changes, then at least you can narrow it down. A traditional Fluke 87 is only going to verify your source isn’t on the edge of dropping your whole town or region. Maybe a Fluke 867b you could see a little waveform. One of the newer scopemeters might show something. RFI is a nasty bitch.


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Electrical Contractor
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it was humming louder before the contactor pulled in,
i wouldnt expect a de-energized contactor to hum
If it was humming louder before the contactor was pulled in, why do you think it has anything to do with the humming?
 

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If they're all LEDs now maybe eliminate the contactors?
 

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If they're all LEDs now maybe eliminate the contactors?
I would be surprised if contactor has anything to do with it. It's the old troubleshooting dilemma, it takes time and what result will be good enough? Maybe on a low load day see if it's buzzing and if not power up loads one at a time or one type at a time and at least find the major contributors. Then bulbs, dimmers, power supplies? I bet you have some crummy LED drivers somewhere.
 

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Residential, lite comm., Industrial
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If they're all LEDs now maybe eliminate the contactors?
It is probable that you would have to rewire the switch from the contactor to the load. Even then the switch may not handle the harmonics and possible inductive load from the drivers (think arcs).
Much better to leave the contactor, it isnt hurting anything or making the noise
 

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It is also highly possible that the coil of the contactor is weak and not pulling the contacts in enough to make a good connection. thus, Chatter (noise) is the result. I agree with previous comments, If you have another contactor, try switching it out or the old trouble shooting rule of process of elimination, disconnect one light at a time till you find the culprit
 

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Scada Supervisor
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Is it possible it's the harmonics from the dimmer causing vibration / resonance that you'd hear?
@DashDingo What neutral bar, the cross bar or the connection strip?
Have you tried removing the mounting screws for a test.
Could the noise be coming back up a conduit?
 

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My best guess is that switched power supply harmonics from the LED packs are being picked up by the coils in the breakers and the vibration in the breaker is being transmitted to the panel which is then acting as a sounding board. Sort of like a loudspeaker. A different make of breaker on that circuit may not have the same resonances — would be worth a try. The right thing to do is to replace the offending LED packs for better quality ones.
 

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Discussion Starter · #39 ·
My best guess is that switched power supply harmonics from the LED packs are being picked up by the coils in the breakers and the vibration in the breaker is being transmitted to the panel which is then acting as a sounding board. Sort of like a loudspeaker. A different make of breaker on that circuit may not have the same resonances — would be worth a try. The right thing to do is to replace the offending LED packs for better quality ones.
I actually suggested to the operator of the building that it not a hazard and that if he wants us to proceed we can isolate the problem LED wall packs and replace with a different brand.


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How sure are you its the neutral bar? I hear noisy old breakers every so often. Even on a couple brand new breakers I've heard some scary noises coming from inside. I would consider a mechanic's stethoscope if I was chasing noises like that.. though the thought of probing a live panel with a metal stick tied to my head makes me pause. Is there such thing as a non conductive electrician's stethoscope?
 
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