Service factor in sizing motor wire size

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ktm400sx

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So I size the wire at 125% of full load, but do I take S.F. into consideration? This is a 460volt 3 phase 1200rpm motor
Also, there will be a soft start and bypass contacter with thermal overloads in a can starting this motor. The bypass contacter is sized in order to start the motor across the line in case of soft start problems.
Since the soft start has thermal protection (electronic) and the bypass contacter has overloads, can I use a mag break circuit breaker to feed the can, or does it have to be thermal magnetic?
Thanks for your help.
 
Let's parse this out, you have several issues in play here.

1:
So I size the wire at 125% of full load...
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You size conductors for 125% of the NEC table 430.250 FLC chart, UNLESS the motor is low speed or high torque and the nameplate current is HIGHER than what is on the chart, THEN you use 125% of the actual nameplate FLC. But that last part is actually somewhat unusual.

2:
... but do I take S.F. into consideration?
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SF is not used in the conductor ampacity determination, only the NEC table is permitted to be used. SF is only a consideration in the selection of overload devices, and only if you plan on using it continuously, which is a bad idea.

3:
Also, there will be a soft start and bypass contacter with thermal overloads in a can starting this motor. The bypass contacter is sized in order to start the motor across the line in case of soft start problems.
Since the soft start has thermal protection (electronic) and the bypass contacter has overloads, can I use a mag break circuit breaker to feed the can, or does it have to be thermal magnetic?
Thanks for your help.
Click to expand...
The soft starter or bypass with overload has no bearing on this. You cannot use a Magnetic Only circuit breaker in the field under any circumstances. They can only be used by the manufacturer of the motor starter, and even then only if the SPECIFIC starter has been designed and UL listed with that SPECIFIC Mag-Only breaker. Only the companies that make both soft starters AND breakers can afford to go to that expense, even some of them don't bother so they just use Thermal Mag breakers anyway.
 
According to 430.6 A(1) Motors under 1200 rpm are sized according to nameplate FLC. Since this has an RPM of 1183 I use motor FLC.
That section says nothing about service factor.

Thanks again
 
That is a 6 pole 1200RPM base motor speed, which is what the NEC is referring to. The nameplate speed is the slip speed, it is always a little lower. But if the FLC is higher than the nameplate, nobody is going to ding you for over sizing the conductors a little. If however the nameplate is UNDER the NEC chart, you must use the chart as your basis.
 
Jraef said:
That is a 6 pole 1200RPM base motor speed, which is what the NEC is referring to. The nameplate speed is the slip speed, it is always a little lower. But if the FLC is higher than the nameplate, nobody is going to ding you for over sizing the conductors a little. If however the nameplate is UNDER the NEC chart, you must use the chart as your basis.
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Gotcha. Thank you
 
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