Circuit breakers vs. contactor heaters

Awl --
Does it make a big diff if I retire my various motor starters, and just use plain ole toggle switches protected with circuit breakers? Seems to me they
do pretty much the same thing. Too much drama wiring up these contactors.
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EA




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Yes, it does.
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Does it make a big BIG diff??
Ahm thinkin the heater wires in these contactors are sized better to a specific motor hp, so then mebbe I could just use smaller breakers.... altho perhaps 15 A is the smallest breaker I could get.... BUT, for 5 hp at full load, sumpn on the order of 20 A might be drawn, so a 15 A breaker should provide heater-like protection, no?? Mebbe too much protection.....
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EA


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On 8/15/2012 3:30 AM, Existential Angst wrote:

Besides overload protection you have to look at contact make/break ratings. Ordinary switches aren't typically rated for that kind of switching load.
Not enough data by any stretch to say much other than there's a reason for motor starters---one of which hasn't been touched and that is protection from automagic restart after a power glitch is a _BIG_ safety factor that goes away w/ a mechanical switch.
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Existential Angst wrote :

WOT'sYour real problem?????
Why do you want to reinvent the electric motor world that all operates quite well the way it is and has been for about 100 years. :-?
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John G



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    Depends!
    For three phase, you either truly want a motor starter, or a VFD (which adds the functionality of a starter).
    The starter has heater elements which will cause the circuit to *all three* phases to open if any one of them draws too much current for too long. The timing matches what is needed to protect a motor, but is long enough so it ignores the high starting current.
    You can get away with protecting a single phase motor with just a circuit breaker -- with the understanding that the breaker may be more likely to trip on starting current -- or be unlikely to trip when a motor is drawing enough extra current to overheat over a fairly long period of operation. Most breakers are too quick at tripping on starting currents, and not quick enough for certain levels of overcurrent.
    How big a motor are you talking about? I figure that up to about 1-1/2 HP the breaker is probably enough, and from 2 HP up I would want a starter or a VFD. (Most 2HP and higher motors are likely to be three phase anyway. :-)
    Enjoy,         DoN.
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