Fuse SIZE (not rating) question

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sigshane

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Hey guys. I have in my hand two fuses. Both rated 600VAC, 30A, time delay, current-limiting, 200kA RMS. Identical ratings, as far as I can tell.

One is 2-inches long, and 1/4-inch in diameter, and the other is 6-inches long, 1.25-inch diameter.

What is the functional, applicable difference between these two fuses, aside from the fuse holder size?
 
sigshane said:
Hey guys. I have in my hand two fuses. Both rated 600VAC, 30A, time delay, current-limiting, 200kA RMS. Identical ratings, as far as I can tell.

One is 2-inches long, and 1/4-inch in diameter, and the other is 6-inches long, 1.25-inch diameter.

What is the functional, applicable difference between these two fuses, aside from the fuse holder size?
Click to expand...

what are the fuse types? Type J? RK?
 
I'm skeptical of the smaller ... I cannot imagine a 600VAC 200 kAIC 30A fuse that small. I'm puzzled by the larger. The common FRS-30 by Bussmann and TRS-30 by Shawmut are 5"x0.81" in 30A.

I was doing control panel design in the early 80s when the Class J time delay was developed; it's reason for existence, we were told, was as a smaller RK5 similar product, albeit more $$. I've not kept up with fuse technology well in the last 10-15 years.

Can you give more details on what you have?
 
sigshane said:
Hey guys. I have in my hand two fuses. Both rated 600VAC, 30A, time delay, current-limiting, 200kA RMS. Identical ratings, as far as I can tell.

One is 2-inches long, and 1/4-inch in diameter, and the other is 6-inches long, 1.25-inch diameter.

What is the functional, applicable difference between these two fuses, aside from the fuse holder size?
Click to expand...
You have manufacturer name and designation on both?

There are midget fuses that are 500 volt rated, 2 inch long sounds close but they are more then 1/4 inch diameter - maybe close to 3/8. These are not RK5 rating.

30 amp 600 volt RK5 fuses are maybe about 6 inches long but are not 1.25 inch diameter - probably close to 3/4 inch diameter.
 
1/4" wide? Are you sure? That's a little small to be a current limiting fuse.

It's more likely you are looking at a Class CC fuse (13/32" wide). CC originally meant "Control Circuit", to be used as primary fuses for Control Power Transformers, then eventually the offering was developed and has evolved to be essentially just as good as their original RK5 cousins, but the one key difference is that the Current Limiting values are different. Most people designing new equipment that needs fuses 30A and under tend to gravitate toward the CC fuse sizes, because the holders and disconnect switches can be smaller. But still, that MUST be reconciled with the let-through data if being used to replace an RK-5 fuse. The RK-5 has a lower let-through profile, so you will often see other devices that need to be in coordinated series strings use the RK-5, and you would NOT be able to substitute the CC equivalent for them (unless specifically tested that way).

And CC fuses are not the same as RK-5. They have the same 200kA interrupt rating, but the CC or the K are the designations for the physical size (the "R" in RK is for Rejection type within Class K, because Class K is interchangeable with Class H, so adding the rejection clips meant they could no longer accidentally install a Class H non-current limiting fuse into the holder). So if they are not the same physical size, they are not "both RK".
 
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