# Class CC Fuses



## SpaceMonkey (Sep 19, 2018)

Why does the NEC allow you to size time delay class CC fuses to 300% instead of the normal 175% for short-circuit and ground fault protection for time delay fuses on motor branch circuits?

Why is class cc treated differently then other time delay fuses? Would you guys recommend sizing to the recommended max of 300%?


----------



## telsa (May 22, 2015)

You realize that CC fuses are small and designed for control circuits?

They fit the clips you'll find on many control transformers -- and no end of DIN rail gadgets.

Since they feed inductors ( relay coils ) they experience starting surges that are quite high.

The slack given by the Code is there to eliminate random trips.


----------



## frenchelectrican (Mar 15, 2007)

SpaceMonkey said:


> Why does the NEC allow you to size time delay class CC fuses to 300% instead of the normal 175% for short-circuit and ground fault protection for time delay fuses on motor branch circuits?
> 
> Why is class cc treated differently then other time delay fuses? Would you guys recommend sizing to the recommended max of 300%?


The class CC is most common used on control transformer and some loads due compact size but they are pretty fast time delay fuse so they will blow little quicker than convential time delay fuse. 

I sized to 250% most case but few I will push more but if you follow the fuse chart vs load you will see why and check with the equipment manufacter to see the listing on class CC fuse rating.


----------



## oliquir (Jan 13, 2011)

i always use the ferraz fuse calculator that will tell you all the maximum fuses sizes and different type of CC fuses. 

https://ep-us.mersen.com/resources/product-selector-tools/select-a-fuser-online/


----------



## JRaef (Mar 23, 2009)

Even though they are both time delay, Class CC have different characteristics than other types of BCP fuses, like Class R or J. Class R and J time delays are based on a 500% current value (500% for 10 seconds) whereas Class CC is based on a 200% value (200% for 12 seconds), making them a little more sensitive to high peak current surges.


----------

