RK1, RK5: Popular Fuses for Motors and Transformers
by Greg Carter
Power fuse safety and test procedures have been established by the U.S, Europe and Asia as performance standards. Power fuses standards of low-voltage (600 volts or less) have evolved into distinct classes. The most common classes are RK1, RK5, G, L, T, J, H and CC.
Previously we’ve discussed Class J, L and T power fuses and the importance of selecting the correct fuses for an application. Not only when you first specify them, but also when you replace them. To aid in selection, manufacturers produce fuses designated by class.
Let’s now focus on Class RK1 and RK5 fuses which are high performance fuses rated 1/10-600A in 250Vac and 600Vac ratings. Many are dual rated and can be used in dc applications.
All are current limiting and carry a 200kA interrupting rating. Some are self-certified up to 300kA IR. Most RK fuses are time-delay dual element design. Fast acting RK fuses are also available for sensitive or critical component protection applications. Class RK fuses are commonly used in mains, feeder and branch circuits, motors, transformers, solenoids and general purpose circuits.
Class RK1 vs. RK5: What’s the Difference?
Class RK1 and RK5 fuses are the same physical size, but Class RK1 fuses are more current-limiting than Class RK5 fuses. This means Class RK1 allow less damaging energy to pass through them while opening (blowing).
Class RK1 Dual-Element Time-Delay Fuses are interchangeable with RK5 according to UL equipment listing conditions and are specified as practical and economical for upgrading systems.
Recommended applications for RK1 fuses are the same as RK5 in most cases and as mentioned above, they offer greater current limitation.
Class RK5 Dual-Element Time-Delay Fuses are the most prevalent fuses in industry for their economy in most applications, especially in motors and transformers.
What is Time Delay Dual Element?
Time Delay Dual Element Fuses have internal construction with separate time-delay overload dual elements that interrupt over-currents to approximately 500%-600% of their nominal rating. This allows fuses to be sized more proportionate to inductive loads such as motors and transformers.
Why Choose Fast Acting?
Based on the equipment being protected you can choose fast acting RK fuses for application specific protection of sensitive devices and critical components. Fast acting fuses are recommended for circuits having a high percentage of non-inductive loads such as heating and lighting.
Specifying and Selecting Fuses for Circuit protection
The fusing market is filled with a wide array of choices, requiring more details in correct fuse sizing and selection. Fuse applications today involve many types of power systems that require an understanding of fuse types, construction, and operational use.
Understanding the fuse characteristics of the various fuse classes simplifies specifying and selecting fuses to avoid mistakes that could jeopardize equipment and component systems. Proper fuse selection depends on many factors, so consult a professional engineer for your application.
The detailed information manufacturers publish today demonstrate this. Stay up-to-date with ongoing developments in types, constructions, characteristics, and classes. Listed below are links to manufacturer datasheets and other educational resources.
Monster Fuses and OEM RK Fuse Resources
|OEM||Monster Fuses Catalog||OEM Specifications|
|EATON Edison||RK1 & RK5||RK1 LENRK, LESRK|
|EATON Edison||RK1 & RK5||RK1 NCLR, SCLR|
|EATON Edison||RK1 & RK5||RK5 ECNR, ECSR|
|EATON Bussmann||RK1 & RK5||RK1 LPN-RK, LPS-RK|
|EATON Bussmann||RK1 & RK5||RK1 KTN-R|
|EATON Bussmann||RK1 & RK5||RK1 KTS-R|
|EATON Bussmann||RK1 & RK5||RK1 KWN-R, KWS-R|
|EATON Bussmann||RK1 & RK5||RK5 FRN-R|
|EATON Bussmann||RK1 & RK5||RK5 FRS-R|
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