Confusing Motor code question

[Final Cut]

I’m going thrugh Mike Holts “electrical exam prep chapter 7”
I felt very confident after hours of studying, until he threw in the 430.55
What the heck is “combined branch circuit overcurrent protection”?
Hours of studying branch, and feeder calculations and all of a sudden it’s like, meh, just use one box at 125% and you’re done.

 

[ActionDave]

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.

Protection for motors comes in two parts
1. Short circuit and ground fault protection
2. Overload protection

You size the circuit breaker or fuse that protects the wires and the motor from a ground fault or short circuit off of table 430.52 and you size the overload that protects the motor based on 430.32 and the nameplate of the motor. Normally those are two separate things, as in a breaker feeding the wires to a motor starter and the starter having the thermal overloads that protect the motor.

 

[Jraef]

The “official” term for these devices is called an “MPCB”, for Motor Protection Circuit Breaker. It’s a thermal-mag circuit breaker where the thermal trip is dial adjustable, just like an overload relay. They were popular in Europe and other places outside of North America, but fur a long time, UL had a problem allowing them to be used on branches because of the adjustable thermal trip. But they have been accepted for over 20 years now, they are just not as well known here yet.

 

[don_resqcapt19]

The “official” term for these devices is called an “MPCB”, for Motor Protection Circuit Breaker. It’s a thermal-mag circuit breaker where the thermal trip is dial adjustable, just like an overload relay. They were popular in Europe and other places outside of North America, but fur a long time, UL had a problem allowing them to be used on branches because of the adjustable thermal trip. But they have been accepted for over 20 years now, they are just not as well known here yet.

You can also use time delay fuses for this purpose, correct?

 

[tortuga]

You can also use time delay fuses for this purpose, correct?

Where 430.32(A)(1) refers to 'separate overload device' I always read that to include among other things a time delay fuse or breaker like when guided by 430.42.

 

[TX+ MASTER#4544]

I’m going thrugh Mike Holts “electrical exam prep chapter 7”
I felt very confident after hours of studying, until he threw in the 430.55
What the heck is “combined branch circuit overcurrent protection”?
Hours of studying branch, and feeder calculations and all of a sudden it’s like, meh, just use one box at 125% and you’re done.

Final Cut poster

2023 NEC

Section 430.55 Combined Overcurrent Protection
You can combine motor branch circuit short circuit and ground-fault protection AND motor overload protection shall be permitted ..........

That means you can use a duel element time delay fuse to serve as both overload protection AND for your branch circuit short circuit and ground fault protection in lieu of providing separate protection for each part.

You must conform to Section 432.52(C),so you can't round up to the next fuse size when you calculate the overloads (heaters).

Thanks for reading
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TX+MASTER#4544