It's the same bang you can hear in the pipe when there is a fault and the breaker trips in the instantaneous region. With an incandsceant lamp or other short but high wattage resistive heating element connected directly to the line, for that first cycle it's essentially a dead short until it heats and the resistance increases.
Why do wires rattle in EMT when some motors start?
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It's the same bang you can hear in the pipe when there is a fault and the breaker trips in the instantaneous region. With an incandsceant lamp or other short but high wattage resistive heating element connected directly to the line, for that first cycle it's essentially a dead short until it heats and the resistance increases.
And yes, twisting the conductors has always been the go-to solution.
It's not always a 'bang' in a ground fault. When there's multiple paths for ground fault current, which there almost always is in a building, that's when you here the Braaaaat! And in the case of a 120 volt circuit for instance, that's the line conductor carrying much more current than the neutral making it impossible to avoid magnetizing the wires. Different phenomenon.
I never said anything about a ground fault, but I distinctly remember hearing the single bang when I had a pinched wire in a MC tail coming off a EMT fed box. I guess I am good at making up my grounds.
In a 120v circuit how is the line conductor carrying more current than the neutral?
My laser printer receptacle is 20A 120V H-N-G in the pipe.
You didn’t say it was a single phase motor...
(Or at least I hope I didn’t miss that)
Getting a single phase motor started is tough on components.
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Did you mean phase to phase fault? I don't see how a phase to phase fault could cause copper conductors to become magnetized, assuming they're ran proximate to each other.
Doesn't matter if it's 120 v, 220 1-phase, or 3-phase. It's just easier to visualize a 1-phase waveform.
Yes, it does...
The three voltages have different wave forms starting a motor
Because in a fault condition. Imagine you have (x)amps flowing back to your source on your grounding conductor. It hits a receptacle box and (x/y)amps jumps onto the steel studs, some splits off through a metal pipe, structure, ect. Almost ALWAYS are there parallel paths for ground fault current back to the transformer. There should never be parallel paths for your hot conductor.
Yes, I know. Offset by 120 degrees. Any point in time represented by a vertical line through this waveform should add to (almost) zero. I'm not explaining my point well.
Phase to phase faults make the conductors repel due to the field generated around the conductor when huge amounts of current move through it.
Here is an example:
And Yes. Being good at making up your grounds provides a LOW IMPEDANCE path for fault current. So MOST of your fault current is proximate to your line current. But a fault 200' from the panel with no grounding conductor in a steel trussed building? BRAAAAAaaaaaaat! We've all heard it.
Read the context associated with that video.
" The cable cleats provide restraint and prevent excessive cable movement resultant from fault-current magnetic forces – cleats must be suitably rated for cable size (outside diameter) and anticipated fault current (peak fault level kA). "
I see nowhere on their website where they use the phrase "phase to phase". Phase to phase fault current is a whole different animal than ground fault current with respect to physical bracing of busses and conductors.
And no, I'm absolutely not referring to anyone on this thread or on this website for that matter. The electrician that knows it all has no reason to debate, to think, or to question. You all do.
You are the elite.
Cheers.
It won’t, and 120 or 240 split phase isn’t separated by 120 degrees.
Right, so take that peak fault current tearing apart metal cable ties and repelling the cables a couple feet apart and scale it down to 50-100 amps hitting some 12ga wire hanging free in a pipe and it will move enough to hear it.
synchro
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Consider two parallel wires separated by a distance R that are flowing equal currents I in opposite directions. The magnetic fields that encircle each of these two wires will therefore circulate around their respective wire in opposite directions (i.e, they'll have opposite polarity). And so as you move away from the pair of wires, their magnetic fields will cancel each other as others have noted. But in the space between the two wires the circulating magnetic fields will be going in the same direction and actually add to each other, not subtract. Think of it like two gears that are meshing and rotating in opposite directions, but right where the gears make contact they are moving in the same direction. Because the magnetic fields created by the wires have the same polarity there will be a repulsive force between them. The strength of that force will be proportional to I2/R by Ampere's force law. And so the repulsion force will go up quickly as the current is increased.
Now I think the rattling is caused when the force is: 1.) sufficiently large to overcome friction, gravity, wire stiffness, etc. that will otherwise keep it in place, 2.) the duration of the force is long enough and it's sufficiently strong to accelerate the wire and move it a large enough distance to cause a rattle, and 3.) the duration of the force is limited, because otherwise the wires will likely just move to another place and stay there (i.e., another equilibrium point) instead of jumping and returning back which I think would be more likely to cause a rattle. A constant application of 60Hz current will create a repetitive force that peaks every 1/2 cycle of 60Hz, but the inertia of the wires should prevent that from causing any significant movement over each 1/2 cycle (probably at most a buzzing noise) . So I'd expect 60Hz to have a similar effect as DC. It shoud be noted that the polarity of the AC current changes each 1/2 cycle, but the direction of the resulting force between the wires is the same (repulsive) because the currents are still flowing in opposite directions.
By the way, I found the following that shows waveforms of the surge current from the heat lamp of a fuser in a laser printer:
Now I think the rattling is caused when the force is: 1.) sufficiently large to overcome friction, gravity, wire stiffness, etc. that will otherwise keep it in place, 2.) the duration of the force is long enough and it's sufficiently strong to accelerate the wire and move it a large enough distance to cause a rattle, and 3.) the duration of the force is limited, because otherwise the wires will likely just move to another place and stay there (i.e., another equilibrium point) instead of jumping and returning back which I think would be more likely to cause a rattle. A constant application of 60Hz current will create a repetitive force that peaks every 1/2 cycle of 60Hz, but the inertia of the wires should prevent that from causing any significant movement over each 1/2 cycle (probably at most a buzzing noise) . So I'd expect 60Hz to have a similar effect as DC. It shoud be noted that the polarity of the AC current changes each 1/2 cycle, but the direction of the resulting force between the wires is the same (repulsive) because the currents are still flowing in opposite directions.
By the way, I found the following that shows waveforms of the surge current from the heat lamp of a fuser in a laser printer:
Let's not get sideways. Fault current, of any type, is not what magnetizes conductors when a motor starts.
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