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How does large over currents passes through a device during turn-on

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MrAl:

--- Quote from: Jwillis on January 03, 2019, 12:15:00 pm ---"Inrush Current" or "Over Current" are really inaccurate ways to describe whats really going on.Current can't "travel" on it's own .It must have a  Closed circuit for it to "travel". What is really going on is Over Loading during turn on. This over loading occurs anywhere in a circuit where there is a capacitance or an inductance. Because both inductors and capacitors act like dead shorts just at start of charge And the load decreases until they are fully charged. At full load the full amount of current available to those components passes through them causing heat.This over loading is what can cause the damage to other components in the circuit. When turn occurs at near or at  the 180 degree cycle Of an AC circular sine wave ,over saturation of the main transformer occurs distorting the field of the core creating high voltage transients which pulls up the available current which further increases the heat created at the source of load.All this heating shortens the life of all components in the circuit.At lower voltages and current,the amount of over loading is quite small and usually won't require current control .It becomes more serious with very high voltages and high currents.
Since motors are essentially inductors ,the coils also act like dead shorts until a field is formed.Ac motors will act just like a transformer because the field also becomes distorted causing over saturation creating transient voltages there by drawing more current from the source at start up.
Reminds me of a 600 volt motor that was started with full mechanical load (a loaded water pump)and a faulty soft start.Blew the thing and the shed it was in to pieces.
Light bulbs are also dead shorts until the filament begins to heat creating a higher resistance .A high resistance has low load and low resistance has a high load.

--- End quote ---

Hi there,

"Inaccurate" to who?  :-)

"Inrush current" is a common way to describe this even though current usually circulates.  It is like many other terms and phrases we as humans use, it is an abstract concept, and abstract is always so darn abstract :-)

If you really want to get down into the mud here though, there are some people who will argue that we cant say "current flow".  That's because they recognize the fact that "current" is already something that flows (electrons) so saying "current" is like saying "electron flow" and so saying "current flow" is like saying "electron flow flow" which sounds strange because of the two instances of the word "flow".

So this is what terminology does to us sometimes. In spite of the ones that seek to change all this, phrases like "current flow"  and "inrush current" and "surge current" are accepted and more to the point are understood to mean the same as if we just said for example "current".

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