Motors Other Than Continuous Duty

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finhead

Senior Member
Can someone help me to understand Table 430.22(E)?

For example: An intermittent duty freight elevator motor requires conductors rated at 140% of nameplate FLC for motors rated continuous duty. So -- if the continuous duty motor is run continuously, conductors must be rated 125% of table FLC. If, on the other hand, the continuous duty motor is run intermittently, conductors must be rated 140% of nameplate FLC.

It makes no sense!

If that is not confusing enough, a 5-minute rated motor running the same freight elevator shall be permitted to have conductors rated 85% of nameplate FLC

Any comments would be greatly appreciated
Brian Dolan
 
Brian,

I'll give it my best guess, if you have a cont. duty motor running intermittently

the stopping and starting ( that it is not made for ) gets the motor running

hot, and hot has to come from somewhere, I guess in the form of additional

current. The cont. duty motor running all the time, keeps cooler by the internal fan.
 
Motors other than continious duty

Motors other than continious duty

I believe this question was asked some time ago possibly last year. If I remember correctly no one could answer it then either.

I would think if you go back to the substatitation for the table from the code making panel that approved it maybe one of them could explain what they had in mind. If any of them are still alive.

As far as I am concerned the table is easy to apply; but I agree it dose not make sense as to why the better the type of motor you would use the larger the conductor would have to be.

Bowhunter
 
The NEC Handbook states the reason for the requirements of 430.22E is because the frequency of starting the motors and duration of operating cycles imposes varying heat loads on the conductors.
 
The NEC Handbook doesn't seem to explain why a continuous duty motor would require larger conductors than a 5-minute motor if they are both performing the exact same task.
 
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