Why do wires rattle in EMT when some motors start?

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Slip.

Now that I've said it, it becomes an "oh yeah no sheeet" moment. Slip offsets the current peak from the voltage peak. Tugging the 'current string' pulls the peak left on one phase and right on the other.

Undersized conductors amplify this along with many other factors. But slip CAUSES it. And for the life of me I'n never ever been able to find this answer on the internet.

Apologies for being mysterious and leading. It's just that I've never been able to explain this, and never seen an explanation. Ever.
 
sdbob said:
Slip.

Now that I've said it, it becomes an "oh yeah no sheeet" moment. Slip offsets the current peak from the voltage peak. Tugging the 'current string' pulls the peak left on one phase and right on the other.

Undersized conductors amplify this along with many other factors. But slip CAUSES it. And for the life of me I'n never ever been able to find this answer on the internet.

Apologies for being mysterious and leading. It's just that I've never been able to explain this, and never seen an explanation. Ever.
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For a cage induction motor slip is around around 6-8 times at starting. It's at around 1760 rpm for a 4-pole motor. That help?
 
Todd0x1 said:
Really, why? Both are wires moving away from eachother when high amounts of current are flowing through them.
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When an electron in 1 wire moves to the right, an electron in the other wire moves to the left, thereby "almost" eliminating the need for either conductor to generate a field, break it down, and regenerate in the opposite polarity.

Someone smarter than me can answer why this manifests with large laser printers but I suspect it has something to do with them requiring almost perfect waveforms in the first place.
 
Disclaimer.
I reserve the right to be wrong.
But go forth and search for slip being related to vibrating conductors. I haven't found it.
 
Besoeker3 said:
I think I might have worked that one out some decades ago...............................:)
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By the way, Besoeker... wild guess there's Nordic blood here. Spent a few hours this weekend tracing my name back to some dude named Olaf in the 16th century.
 
sdbob said:
When an electron in 1 wire moves to the right, an electron in the other wire moves to the left, thereby "almost" eliminating the need for either conductor to generate a field, break it down, and regenerate in the opposite polarity.

Someone smarter than me can answer why this manifests with large laser printers but I suspect it has something to do with them requiring almost perfect waveforms in the first place.
Click to expand...
Its not a continuous rattle, just one movement at the point the high inrush occurs when the fuser turns on. This is a resistive load.

I think i found the answer. When current flows in opposite directions in two parallel wires, they want to repel each other. Its always happening but it takes alot of current to make the wires move.

https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/parallel-wires the example here of a series circuit in DC would mimic what's happening in a normal AC circuit.
 
Todd0x1 said:
Really, why? Both are wires moving away from eachother when high amounts of current are flowing through them.
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Transients defined as:
(ANSI std. 1100-1992) A sub cycle disturbance in the AC waveform that is evidenced by a sharp brief discontinuity of the waveform. Transients may be of either polarity and may be of additive or subtractive energy to the nominal waveform.

Switching transformers, ballasts ect all cause transients, but ESPECIALLY laser printers. Still a malformed waveform. but different than slip.

Yes, I had to look that up.
 
Todd0x1 said:
Its not a continuous rattle, just one movement at the point the high inrush occurs when the fuser turns on. This is a resistive load.

I think i found the answer. When current flows in opposite directions in two parallel wires, they want to repel each other. Its always happening but it takes alot of current to make the wires move.

https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/parallel-wires the example here of a series circuit in DC would mimic what's happening in a normal AC circuit.
Click to expand...
So this example shows current moving through a conductor causing a magnetic field. If that wire is folded back on itself those fields are opposing. Totally different.
 
sdbob said:
By the way, Besoeker... wild guess there's Nordic blood here. Spent a few hours this weekend tracing my name back to some dude named Olaf in the 16th century.
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My Scots ancestry goes a long way back. I known family is back to the 1745 revolution. And Prince Charlie.
 
sdbob said:
So this example shows current moving through a conductor causing a magnetic field. If that wire is folded back on itself those fields are opposing. Totally different.
Click to expand...

In a DC circuit. In a AC circuit current is moving forward on one wire and in the opposite direction on the other wire.
 
sdbob said:
Transients defined as:
(ANSI std. 1100-1992) A sub cycle disturbance in the AC waveform that is evidenced by a sharp brief discontinuity of the waveform. Transients may be of either polarity and may be of additive or subtractive energy to the nominal waveform.

Switching transformers, ballasts ect all cause transients, but ESPECIALLY laser printers. Still a malformed waveform. but different than slip.

Yes, I had to look that up.
Click to expand...

Transient due to the high inrush current. Same as switching on a cold 1kw halogen lamp.
 
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