Strange Humming in Panel

MD Automation said:
It brings back tons of memories for me, of heading to the hardware store to buy those EverReady batteries
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Yeah I used to go down the block to "Kleber's Hardware" to buy them. While I was there Mrs. Kleber used to give me fruit from her garden and honey from her bees. (They were friends of my grandparents). They were both German immigrants, and I was a little blond haired blue eyed German kid who was festinated with everything in their store, so,,,,,,,,,,,,,

It was an almost Norman Rockwell thing
 
Berger Hardware for me. Used to ride my bike down to it when I was 9. The owner's son was my age and we got to know each other. Years later when his father passed away, he took over the business and when he decided to retire he sold to a new owner who went with True Value. True Value came in and completely redid the store. The original owner's son had stayed on as a "consultant" and called me to say that they would be throwing out a bunch of stuff that was there for years and there's a lot of wire I might be interested in. It was mostly reels of CAT3 telcom stuff that I had a use for at that time.

-Hal
 
Joe and MD
Curious just
As kids playing magnets
Remember ever wondered why magnets attract as child Albert Einstein done?
 
Yes the strict definition of magnetostriction includes movement, and it's resulting noise, of any ferromagnetic material. However as, the linked document explains it is not a primary, or likely, source of humming noise in a breaker.
As the adage says 'when you hear hoof steps, think of horses not zebras' (unless you live in Africa).
 
jim dungar said:
Maybe, but not due to magnetostriction.
The magnetic portion is usually an electromagnet core made of a solid metallic piece with no laminations, in the shape of a U, while the moveable piece is often part of the bimetal used for the thermal portion.
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I think you are mistaken about magnetostriction being limited to laminated pieces. Magnetostriction is found in all ferromagnetic materials, solid, laminated, etc.

But I honestly wasn't thinking about magnetostriction. I was thinking about elements that are supposed to move responding to the magnetic field. I was limiting my statement to 'there is a magnetic coil with circuit current flowing through it, and there are moving parts. If the moving parts happen to mechanically resonate at one of the electrical harmonic frequencies, then it won't take much coupling for the harmonic current flow to create audible acoustic noise'.

-Jonathan
 
winnie said:
I think you are mistaken about magnetostriction being limited to laminated pieces. Magnetostriction is found in all ferromagnetic materials, solid, laminated, etc.
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I understand magnetostriction exists in all ferromagnetic materials. It is just in the real world the primary cause of the audible magnetostriction noise is the movement of the individual sheets in laminated materials. There is less audible noise when parts are not in direct contact and rubbing against each other without lubrication. Most of the parts inside of a circuit breaker are intended to move without a substantial amount of friction against each other. Vibration of loose parts, such as arc chutes, is typically the source of the hum not the magnetostriction in those parts, so the solution is to provide better component mounting and not necessarily change the material to something non-ferromagnetic.
 
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jim dungar said:
I understand magnetonatriction exists in all ferromagnetic materials. It is just in the real world the primary cause of the audible magnetostriction noise is the movement of the individual sheets in laminated materials. There is less audible noise when parts are not in direct contact and rubbing against each other without lubrication. Most of the parts inside of a circuit breaker are intended to move without a substantial amount friction against each other. Vibration of loose parts, such as arc chutes, is typically the source of the hum not the magnetostriction in those parts, so the solution is to provide better component mounting and not necessarily change the material to something non-ferromagnetic.
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Why particular about harmonic resonance, not power frequency resonance
Power quality Issues rampant there?
 
Deltaforce said:
Why particular about harmonic resonance, not power frequency resonance
Power quality Issues rampant there?
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I think that question was directed to me, since I was suggesting that this might be a harmonic issue.

I am claiming that if the magnetic field of the circuit couples to a physical object that resonates at an AC frequency component of that magnetic field, then you can get audible noise. This can certainly happen at the fundamental frequency of the power circuit.

What leads me to focus on harmonics in this case is that the noise went away when the dimmers were replaced with ordinary light switches. The dimmer current waveform is rich in harmonics, even when supplying an incandescent lamp.
 
winnie said:
What leads me to focus on harmonics in this case is that the noise went away when the dimmers were replaced with ordinary light switches. The dimmer current waveform is rich in harmonics, even when supplying an incandescent lamp.
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What bothers/confuses me is ONLY when the breaker for the AC air handler was turned off, then back on, would the arcing/buzzing sound occur. I assume the same thing happened when the unit kicked on during normal operation. The owner says he hears it when the unit comes on. I don't see how replacing the dimmers had any effect on stopping the arcing from a circuit not related to the dimmers.
Just waiting on him to confirm the noise is gone.
 
Little Bill said:
What bothers/confuses me is ONLY when the breaker for the AC air handler was turned off, then back on, would the arcing/buzzing sound occur. I assume the same thing happened when the unit kicked on during normal operation. The owner says he hears it when the unit comes on. I don't see how replacing the dimmers had any effect on stopping the arcing from a circuit not related to the dimmers.
Just waiting on him to confirm the noise is gone.
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Dimmers Harmonics affect other loads through common point of coupling (pcc)
Noise from breaker by magnetostrictive vibrations harmonics amplified into buzzing noise
Now harmonics dimmers gone, magnetostrictive vibrations would still there, felt by touching breaker
 
winnie said:
What leads me to focus on harmonics in this case is that the noise went away when the dimmers were replaced with ordinary light switches. The dimmer current waveform is rich in harmonics, even when supplying an incandescent lamp.
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Little Bill said:
What bothers/confuses me is ONLY when the breaker for the AC air handler was turned off, then back on, would the arcing/buzzing sound occur. I assume the same thing happened when the unit kicked on during normal operation. The owner says he hears it when the unit comes on. I don't see how replacing the dimmers had any effect on stopping the arcing from a circuit not related to the dimmers.
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From what I've seen inside breakers, they typically are made with stamped metal parts sometimes with punched holes, along with other somewhat loosely fitted parts. Clearances and tolerances appear to be relatively generous. That is not a criticism, because they function well and are, for the most part, affordable. But based on this, here's a wild guess at what could be happening. The surge in current when turning the air handler back on may have caused a pulse in the magnetic field from the electromagnet coil in the breaker, which then shifted the metal parts of the magnetic trip function slightly. Maybe the position of the parts and their clearances then allowed an acoustic resonance to be excited by the harmonic currents that Jon mentioned.
If the scenario I just described is happening with this breaker, then due to production tolerances other breakers of the same type may not behave in the identical way.
 
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