Motor Overload Protection question.

[evalencia01]

Hello,

Could anyone make sense of this to me?

For motors other than continuous duty such as intermittent duty, 430.33 says that we can simply use the ground-fault short circuit protective device as an overload device. Which makes it seem like it can be sized according to Table 430.52, but 430.55 says it cannot be greater than what's listed in 430.32.

I don't understand it and was wondering if anyone could clarify how to size the overload of a motor that is other than continuous duty.

Thank you!

 

[don_resqcapt19]

If the motor use complies with this:
"A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty,"
the branch circuit ground fault and short circuit protective device is all that is required.
What is the exact operational usage of the motor?

 

[evalencia01]

It was a practice test question. The motor was intermittent duty and had a service factor of 1.15 and temperature rise of 40C. It's tripped me up since 430.33 tells me to simply use the ground-fault short-circuit protection as the overload protection, but there's a service factor and temperature rise too.

 

[evalencia01]

If the motor use complies with this:
"A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty,"
the branch circuit ground fault and short circuit protective device is all that is required.
What is the exact operational usage of the motor?

It was intermittent duty, 15 minute rated, but it also included a service factor and temperature rise. Would I then instead use 430.32 or stick with 430.33 as it's a trick question?

 

[don_resqcapt19]

430.33 does is not related to the duty rating of the motor, but rather related to the actual operation of the motor. Without something to tell you that the motor operation is in accordance with 430.33, you can't use that rule.