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
Besides overload protection you have to look at contact make/break
ratings. Ordinary switches aren't typically rated for that kind of
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.
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
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. :-)
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