Continuous duty & Continuous Load Motor

[Flapjack]

He did not say that he said "The electrical power input that supplies the mechanical power output is exactly the same for both motors". Which is what I have also been saying. It means the same amount of power is used to drive the load in either case, but there is additional power use in both cases but it is not the same in both.

Ah, I just read it wrong. It makes sense now that you put it in bold. :thumbsup:

 

[Flapjack]

If circumstances had either motor running for 3 hours, you would need to treat the load as 'continuous.'

I don't read anywhere in Article 430 about continuous loads which is why I asked the question. I do however read about 125% for continuous duty in NEC 430.22.

At some point, motor circuit design has to go beyond 'code,' into the specifics of the application. For example, a motor with frequent starts might benefit from larger than code- required wires because of the larger 'starting current' required.

Isn't that what Table 430.22(E) is getting at?


Separate question... NEC 430.6 refers to table values instead of the motor nameplate FLA to determine the ratings of conductors, switches, short-circuit and ground fault protection. Why is this? Is it just more conservative?
(I just graduated last year so I have a lot of questions about parts of the code that I read)

 

[jim dungar]

Separate question... NEC 430.6 refers to table values instead of the motor nameplate FLA to determine the ratings of conductors, switches, short-circuit and ground fault protection. Why is this? Is it just more conservative?

Kind of.

There are no industry rules governing the 'exact' construction of motors nor of their actual application, therefore a replacement (or rewound) motor may have different ampacity values than the original equipment. The National Electrical Manufacturers Association (NEMA) developed some theoretical worst case values. Basically all of its members agreed that any general purpose motors, and control equipment, they build will always be less than these 'design ampacities'. This meant that any general purpose NEMA motor or NEMA controller could be easily applied or replaced. Eventually these maximum design values entered the NEC as the tables we see today.

 

[Flapjack]

Thanks for the explanation Jim.