RK1 and RK5 Fuse Curves

[elen09]

Hello, I am currently working on a project and need some information on RK1 and RK5 fuse curves. The question has arisen if all bussmann, edison, littlefuse, and ferazz/shamute fuses are the same, ie interchangable.

 

[davidbeach]

The curves are not identical, but are similar. The physical size is standardized.

 

[Zogzog]

Go to the fuse manufacture website for curves and cross references between fuse manufactures.

 

[elen09]

I know there is a slight difference between the curves, but I need to know if that difference is signifigant. I know that medium voltage fuses do have signifigant differences and more thought goes into the selection. A similar claim has been made about RK1 and RK5 fuses and it is my task to determine if there differences are relevent. I have not been able to find literature on the subject, and would like to know if anyone out there has?

 

[DanDel]

The slight difference between curves is only significant if part of the curve impedes upon another curve in a coordination study. Are you concerned about coordination?

 

[Zogzog]

I ran a quick comparison in SKM and I was suprised at how much of a difference there was, mostly from 0.5 to 30 seconds. If I knew how to attach a file to a post I would post the TCC.

 

[Zogzog]

I would say they are relevant. My study involved a 30A 600V RK1 and RK5 fuse protecting a 20HP motor. the RK 5 allowed for the motor to start, the RK1 did not.

 

[davidbeach]

RK1 and RK5 are quite different from each other. A Bussmann RK5 and a Littelfuse RK5 and a Ferazz/Shamute RK5 should all be quite similar. No surprise at all that you couldn't get the motor to start on an RK1, that's what RK5s are for.

 

[Zogzog]

elen09, are you asking about the differences between RK5 of different manufactures or between a RK5 and RK1?

 

[elen09]

Im looking into the differences between a bussmann RK1 and littlefuse RK1, ect. The curves are slightly different, that can be seen with just a glance, what I need to know is if that difference is anything substantial. The equations themselves are trade secrets, so all I have to go on is the graphs. This complicates things further due to the scaling differences between manufactures.

 

[rbulsara]

elen9:

Fuses of the same class and rating of different manucafutrers that you mention are meant to be interchangeable. The differences if any are not significant. The very reason their physical characteristics are standardized is that they "can" be interchanged.

 

[jraef]

...unless in YOUR case the extra let-through or additional clearing time is what allows an arc flash to burn someone or starts a fire, or the reduced clearing time causes a nuisance shut down of a critical machine.

I'm not criticizing rbulsara's answer, merely pointing out that although the INTENT is for the different mfrs versions of the same fuse to be interchangeable, there is no substitute for good engineering practice. In most cases for instance, if you do an Arc Flash evaluation of a system based upon one specific fuse, that evaluation is SPECIFIC to that fuse. If you want something that can accept any brand, you must use the NFPA tables, and the let-through energy is FAR greater than you might get with a more carefully chosen brand because the "generic" chart is based on the lowest common denominator.