Phenomena, oddities, & the counter intuitive..

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under8ed

under8ed

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Charleston, SC., USA
I would love to see posts that may show up in such a thread. Surely others have been surprised by various encounters over the years. Many of these have become common knowledge to us now; but if we recall & post our earlier "Ah Ha" learning moments, others may learn from them. I have jotted down a short list worthy of sharing & will follow with one, although I hope to hear some great ones from others; even if it means we must admit we didn't know what we do now.
 
Normal phenomenon, or an oddity?
This one is similar to the time I heard a Mocking bird perfectly imitating a forklift back up alarm, in that I probably would never speak of it had there not been another credible witness. We had just hooked up a 480v. compressor unit outside a quiet area in the plant. The #6 wire inside was pulled in an over-sized existing EMT conduit. When the unit was tested I thought I heard a noise overhead, so it was done again. Sure enough; every time it started, you could hear the wires twitch, or flex in the conduit. This is the only time I have ever seen or heard of such a thing. Until today at least; I stumbled on this video reminding me of the incident, and prompting this thread. https://www.youtube.com/watch?v=tUCtCYty-ns
I had never really found a good explanation for it, now I wonder if the conduit may have been magnetized by a nearby motor or some other equipment. It was a temporary hook up, so unless someone else has an answer, I may always be guessing.
 
under8ed said:
Normal phenomenon, or an oddity?
This one is similar to the time I heard a Mocking bird perfectly imitating a forklift back up alarm, in that I probably would never speak of it had there not been another credible witness. We had just hooked up a 480v. compressor unit outside a quiet area in the plant. The #6 wire inside was pulled in an over-sized existing EMT conduit. When the unit was tested I thought I heard a noise overhead, so it was done again. Sure enough; every time it started, you could hear the wires twitch, or flex in the conduit. This is the only time I have ever seen or heard of such a thing. Until today at least; I stumbled on this video reminding me of the incident, and prompting this thread. https://www.youtube.com/watch?v=tUCtCYty-ns
I had never really found a good explanation for it, now I wonder if the conduit may have been magnetized by a nearby motor or some other equipment. It was a temporary hook up, so unless someone else has an answer, I may always be guessing.
Click to expand...

If the wires twist and flex inside a conduit, what you are probably noticing is the result of magnetic forces (attraction in most cases) which exist between the wires when a high current is flowing in them.
Two wires with equal current in the same direction flowing through them will be pushed apart by a force which is proportional to the square of the current and inversely proportional to the distance between them (not the square of the distance.)
Two wires with equal current in opposite directions will have a force of the same magnitude but attracting the wires together.
Since the current flowing in AC, the force will go through zero 120 times per second, causing a buzzing, and the force may only be noticeable for the duration of the high surge current from a motor starting.
 
GoldDigger said:
....., what you are probably noticing is the result of magnetic forces (attraction in most cases) which exist between the wires when a high current is flowing in them... ...., the force will go through zero 120 times per second, causing a buzzing, and the force may only be noticeable for the duration of the high surge current from a motor starting.
Click to expand...

I would have expected this may not be so odd after seeing a couple of videos from that page. I suppose the over-size of the conduit, light weight of the wire, and the quiet area were all factors making this incident noticeable. Otherwise, It seems we would hear this fairly often.
 
150322-0916 EDT

GoldDigger:

As I read your description I believe it is out of phase.

If one makes a hairpin loop with the wire spacing close and apply a current thru the loop, then the loop will open because the magnetic fields of the wires are of the same polarity in the space between the two adjacent wires. In the hairpin loop the two adjacent wires have the same magnitude current flowing but in opposite directions.

Two adjacent wires with current going in the same direction will tend to attract each other.

The hair pin loop experiment is easy to demonstrate with about 4 ft of #22 or #24 wire and a 12 V battery. Space the wires about 1/2" or less apart.

.



.
 
gar said:
150322-0916 EDT GoldDigger: As I read your description I believe it is out of phase. If one makes a hairpin loop with the wire spacing close and apply a current thru the loop, then the loop will open because the magnetic fields of the wires are of the same polarity in the space between the two adjacent wires. In the hairpin loop the two adjacent wires have the same magnitude current flowing but in opposite directions. Two adjacent wires with current going in the same direction will tend to attract each other. The hair pin loop experiment is easy to demonstrate with about 4 ft of #22 or #24 wire and a 12 V battery. Space the wires about 1/2" or less apart..
Click to expand...

This is good stuff, the physics of electromagnetism on a level I have never had to think much about during my career. If I understand correctly, the magnetic balance may have been disrupted by simply loosing some length in one of the phases? I understand this comes into play with larger parallel feeders and the NEC addresses this by requiring equal lengths. I expect on those size conductors heat is generated since the wires will not freely move away from each other.
 
Rare phenomenon witnessed?
This is another incident which at the time I could not explain the physics and have since come to better understand it... We were to install a pull rope in an underground conduit from a boiler/compressor room to a manhole outside. The plant engineer and my boss had identified the conduit from the drawings, then went out to let us know when it appeared in the manhole. I was left with help to push in a 1/4" metal fish tape. A few yards in the noisy room went quiet other than a couple annunciator alarms. We went`out to inform them something was wrong, but they knew since a jack had blown on a pole near them. We all walked around the side of the building to find the large, pad mounted, oil filled transformer spewing its contents 30 feet into the air! A cooling fin weld had split at the top.
The tape had turned up into a 4160 v. switch at that pad, shorting & causing the transformer troubles. I was fortunate that the conduit was underground, metal, & wet. There are at least a couple good precautionary lessons that can be taken from this story that seem obvious in hindsight.
Here is a link that explains an oil filled transformer incident, which apparently are not so rare since the article is describing a new safety relief to control these events;(though with the valves, we may never see this again).

http://www.power-eng.com/articles/p...atures/oil-filled-transformer-explosions.html

Ok, anyone else have a story to share?
 
Never saw this in person, just a story from the Boss. Take a 250' coil of Romex, remove the plastic wrap. Connect one end to a motor load. It will supposedly expand like a giant slinky due to magnetic forces.
 
But doesn't the high magnetic field also induce current in the conduit which in turn produces a counter magnetic field?
 
150323-0920 EDT

under8ed:

Consider two long parallel wires spaced close together. Each of those wires has a magnetic field around it. If one wire was in isolation, then there would be circular magnetic flux lines concentrically located around the wire (current flow) (current flow does not require a wire - for example an electron beam in a cathode ray tube). The electron beam in a CRT can be deflected by either an electric field (deflection plates), or a magnetic field. When two wires are brought close together, then the field shape becomes non-circular.

The equation for the force between the wires is F = i^2*um/(2*Pi*D) newtons/meter-of-length. See "Electric and Magnetic Fields", Third Edition. Stephen S. Attwood, 1949, p 213. Book cost $6.50 in 1955.

For every incremental length of the parallel wires there is a force between the wires over that length given by the above equation. Hold everything constant except double the length of wire and the force between the wires is doubled. But force per unit of length does not change.

On page 270 is shown a field map for two parallel wires with opposing currents. That pattern you see is made up of curvilinear squares. A curvilinear square is one with four sides where the intersections at the corners are perpendicular. Half of our senior design course was spent in hand sketching various field maps. The teacher of that course, A. D. Moore, was an expert in fields and had created a method of studying fields via plaster molds and fluid flow. This was before the days of electronic analog and digital computers.

On page 268 is a plot of the magnetic intensity as a function of radius from the center of a round wire with uniform current density in the wire.

The force between two parallel wires is relatively small for moderate currents. To run the experiment I previously mentioned you might find it useful to use solid magnet wire. Slightly overstretch (yield) the wire to make it perfectly straight. Lay the two wires 3/8 to 1/2 inch apart on the bench. Work on a non-magnetic bench. Use Scotch 33 tape to hold the wires at each end of about an approximate 2 ft distance.

Using a hairpin shape wire the two adjacent wires will move apart on application of current. To make them attract break the hairpin loop end and run external wires that are spaced some distance away from the test wires, and wire so that the current in both wires is in the same direction.


Your comments on making wire lengths exactly the same for parallel runs has nothing to do with the consideration of forces between the conductors.

.
 
Last edited:
gar,

I do appreciate your patience in explaining these fields. My paragraph commenting on your last post was poorly worded. I began with "If I understand", but failed to maintain the wording as speculation on the parallel feeders. No credit for the thought process though? I was believing that if larger conductors were experiencing the forces that caused my wires movement, that heat could be generated if they were not free to move.
 
gar said:
150323-0920 EDT

under8ed:

Consider two long parallel wires spaced close together. Each of those wires has a magnetic field around it. If one wire was in isolation, then there would be circular magnetic flux lines concentrically located around the wire (current flow) (current flow does not require a wire - for example an electron beam in a cathode ray tube). The electron beam in a CRT can be deflected by either an electric field (deflection plates), or a magnetic field. When two wires are brought close together, then the field shape becomes non-circular.

The equation for the force between the wires is F = i^2*um/(2*Pi*D) newtons/meter-of-length. See "Electric and Magnetic Fields", Third Edition. Stephen S. Attwood, 1949, p 213. Book cost $6.50 in 1955.

For every incremental length of the parallel wires there is a force between the wires over that length given by the above equation. Hold everything constant except double the length of wire and the force between the wires is doubled. But force per unit of length does not change.

On page 270 is shown a field map for two parallel wires with opposing currents. That pattern you see is made up of curvilinear squares. A curvilinear square is one with four sides where the intersections at the corners are perpendicular. Half of our senior design course was spent in hand sketching various field maps. The teacher of that course, A. D. Moore, was an expert in fields and had created a method of studying fields via plaster molds and fluid flow. This was before the days of electronic analog and digital computers.

On page 268 is a plot of the magnetic intensity as a function of radius from the center of a round wire with uniform current density in the wire.

The force between two parallel wires is relatively small for moderate currents. To run the experiment I previously mentioned you might find it useful to use solid magnet wire. Slightly overstretch (yield) the wire to make it perfectly straight. Lay the two wires 3/8 to 1/2 inch apart on the bench. Work on a non-magnetic bench. Use Scotch 33 tape to hold the wires at each end of about an approximate 2 ft distance.

Using a hairpin shape wire the two adjacent wires will move apart on application of current. To make them attract break the hairpin loop end and run external wires that are spaced some distance away from the test wires, and wire so that the current in both wires is in the same direction.


Your comments on making wire lengths exactly the same for parallel runs has nothing to do with the consideration of forces between the conductors.

.
Click to expand...


Thanks! :)

Now one question, if opposite conductors attract, why would they jump or rattle in conduit in the first place?
 
under8ed said:
gar,

I do appreciate your patience in explaining these fields. My paragraph commenting on your last post was poorly worded. I began with "If I understand", but failed to maintain the wording as speculation on the parallel feeders. No credit for the thought process though? I was believing that if larger conductors were experiencing the forces that caused my wires movement, that heat could be generated if they were not free to move.
Click to expand...

Whether or not they are free to move would have no noticeable effect on the heating of the wires. You are probably thinking that something like a clutch generates lots of heat when it is slipping instead of moving, but the forces on the wires will produce mechanical energy which might lead to frictional heating if the wires are free to move and will not transfer any energy at all if the wires are not free to move.
Similarly a motor winding generates lots more heat when the motor shaft is locked, but that is primarily because the current is so much higher without the effect of the counter-EMF caused by the rotation. In this case the current will be the same whether the wires move or not.
 
under8ed said:
Normal phenomenon, or an oddity?
This one is similar to the time I heard a Mocking bird perfectly imitating a forklift back up alarm, in that I probably would never speak of it had there not been another credible witness. We had just hooked up a 480v. compressor unit outside a quiet area in the plant. The #6 wire inside was pulled in an over-sized existing EMT conduit. When the unit was tested I thought I heard a noise overhead, so it was done again. Sure enough; every time it started, you could hear the wires twitch, or flex in the conduit. This is the only time I have ever seen or heard of such a thing. Until today at least; I stumbled on this video reminding me of the incident, and prompting this thread. https://www.youtube.com/watch?v=tUCtCYty-ns
I had never really found a good explanation for it, now I wonder if the conduit may have been magnetized by a nearby motor or some other equipment. It was a temporary hook up, so unless someone else has an answer, I may always be guessing.
Click to expand...

My daughter had a parakeet that she kept in a cage in her bathroom much of the time. Her bathroom was also the guest bathroom, and I had (still do) a weekly get together with my musician friends to play music and drink beer. One day my wife heard a curious sound like someone was using the guest bathroom, but she was alone in the house. The parakeet was imitating the sound of a thin stream of water falling into a larger reservoir from a height of about 2 feet.
 
Twist wire

Twist wire

under8ed said:
I would have expected this may not be so odd after seeing a couple of videos from that page. I suppose the over-size of the conduit, light weight of the wire, and the quiet area were all factors making this incident noticeable. Otherwise, It seems we would hear this fairly often.
Click to expand...

If it is ever an issue, disconnect wires and twist wires in conduit so they wrap around each other reconnect, problem solved.
 
Oddity repaired without conclusion

We had a large station, (foreign made machining equipment) which began taking out the bus duct when it was turned off for periodic maintenance, (ground fault indicated). This was obviously a problem for our facilities department, (wear & tear on the 800 amp breaker), and the production department, (other machines affected, including several identical); so two separate maintenance groups were looking into this.
I do remember making some improvements on the machine's 400 volt transformer grounding & bonding connections, (not normally installed with an outside contractor, but these were in an relocation agreement from another plant), but I don't recall finding any "Ah Ha" problems.
The problem went away without the other maintenance group reporting any specific findings, but I'm not so certain they would. Either way, this was an odd problem that none had a valid explanation for what exactly could cause it. I had an admittedly wild thought, knowing that a car's ignition spark is caused by the collapsing field in the coil when the points break, (old school); I wondered if there was any correlation with this. Has anyone had a similar incident? Or know exactly what occurred?
 
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