Nec 430.32(c)

[erickench]

The above NEC section provides a solution in case a continuous-duty motor will not start because of the sizing of the overload. It allows the overload device to be increased to either 140% or 130% depending on the service factor or temperature rise. But Mike Holt in his book "NEC Exam Preparation" state's that a motor can be protected against short circuit, ground fault and overload by a single overcurrent device in accordance with the above NEC secton. Does anyone agree with this? I don't see this exemption anywhere in the NEC. This would apply to continuous-duty motors only.:-?

 

[cpal]

are you asking if as single ocpd can provide short circuit, ground fault and OL protection??

or are you asking if section 430.32(C) applies exclusively to cont duty motors?

 

[erickench]

I'm asking if a single OCPD can provide overload, short circuit and ground fault protection. I just looked at NEC 430.55. It refer's to 430.32.

 

[cpal]

is this what you are looking for?

430.55 Combined Overcurrent Protection.
Motor branch-circuit short-circuit and ground-fault protection and motor overload protection shall be permitted to be combined in a single protective device where the rating or setting of the device provides the overload protection specified in 430.32.

 

[erickench]

Well that settled it. It could be done. But I would think that where a single OCPD is used you would have to increase the size of the overload to either 140% or 130%. I mean the short-circuit ground-fault protection is oversized in a circuit where there is already a separate overload.

 

[cpal]

The HB exp notes indicates that 430.32(C) is not applicable under this section.see below


Fuses and circuit breakers are not permitted to be sized as overload protection according to the values of 430.32(C). Rather, fuses are permitted to be sized as overload protection only according to the values found in 430.32(A)(1), 430.32(B)(1), and 430.32(D)(1).

 

[erickench]

Yes but if the motor does'nt start you still have to increase the size of the protection in accordance with NEC 430.32(C). I thought that this would've been a good design precaution just in case.

 

[weressl]

Well that settled it. It could be done. But I would think that where a single OCPD is used you would have to increase the size of the overload to either 140% or 130%. I mean the short-circuit ground-fault protection is oversized in a circuit where there is already a separate overload.

It allows for combination type devices where short circuit and overload protection accomplished by adjustable magnetic and thermal elements. The adjustment is indicidual and does not necessarily means that the thermal element needs to be increased to 130-140%. The time characteristic, the OL class of 10-50 sec. @ 6*In could be adjustable to allow for large load acceleration.