NEC 610.33 Question

[MrCloudy]

I have a question on the wording used in NEC 610.33.

It reads: The continuous ampere rating of the switch or circuit breaker required by 610.32 shall not be less than 50 percent of the combined short-time ampere rating of the motors ...

What is the meaning of the short-time ampere rating of the motors? I looked for a definition in the NEC and on the web and have so far I've been unsuccessful. Did they mean the short time duty rating? Or maybe using the service factor of the motor to get the short time amperage?

Seems like they used a term that isn't really clarified anywhere.

Thanks,

 

[tortuga]

I have a question on the wording used in NEC 610.33.

It reads: The continuous ampere rating of the switch or circuit breaker required by 610.32 shall not be less than 50 percent of the combined short-time ampere rating of the motors ...

What is the meaning of the short-time ampere rating of the motors? I looked for a definition in the NEC and on the web and have so far I've been unsuccessful. Did they mean the short time duty rating? Or maybe using the service factor of the motor to get the short time amperage?

Yes see Table 430.22(E)

 

[MrCloudy]

Ok looking at the table you're saying Short-time ampere rating is the same as a short time duty cycle?

 

[roger]

MrCloudy, please update your profile to show a more accurate location, the state you are in at a minimum

 

[MrCloudy]

Should be updated

 

[tortuga]

Ok looking at the table you're saying Short-time ampere rating is the same as a short time duty cycle?

Thats the way I have always read that.

The NEMA definition for short-time motors is: “All short-time ratings are based upon corresponding short-time load
tests, which shall commence only when the windings and other parts of the motor are within 5°C of
the ambient temperature at the time of the test.”

In the IEC standards its S2 Short-time duty: "The motor works at a constant load, but not long enough to reach temperature equilibrium, and the rest periods are long enough for the motor to reach ambient temperature".

Cranes tend to be built to IEC standards.

 

[MrCloudy]

OK that's what I guessed but I wanted to verify since I couldn't find an answer elsewhere.

Thanks!

 

[roger]

Should be updated

Thank you.