SCCR quandary

Hoping there might be a SCCR guru that could guide me to an answer:

I’m doing some retrofit projects where the panels have to be updated for SCCR since they left the facility. What I have are Telemecanique contactors and overloads with FRS-R fuses in front of them.

I went to the UL website (https://www.ul.com/resources/short-circuit-current-ratings-combination-motor-controller-components) and pulled the spreadsheet for Square-D IEC fuse (SquareD IEC Fuse_04-08-08.xls) and did in fact find my contactors and overloads in all of the panels.

However, they are all listed in combination with a Square-D fuse block for Class J and CC fuses. (GS1GU3 for Class J fuses, GS1DDU3 for CC)
The original panels have a Bussman R600 fuseblock (200kA SCCR) with FRS-R fuses.

So, if I were designing this panel from scratch, I would use those parts recommended. However, the FRS-R fuses have a better rating, are already wired and in the panel. Do I have to swap them out for the Square-D component / fuses in order to achieve the 100kA rating? Is there any leniency on the fuse block that is used?

UL508A SB4.2.3 Exception 1 would let you use an alternate class fuse than the specified fuse if the alternate class fuse has a lower peak let-through than the specified fuse according to table SB4.2.

From what I can see in the table there are no cases where an RK5 fuse has a lower let-through than an equivalent J-class or CC-class fuse. So an RK5 would not be a substitute. If you can't use that fuse type you really can't use that fuseblock.

You don't need to use a SquareD fuse or fuseblock. As long as the fuse is a Class J or CC you can use anyone's stuff and still meet the high fault rating.

Keith

kamenges said:

...

You don't need to use a SquareD fuse or fuseblock. As long as the fuse is a Class J or CC you can use anyone's stuff and still meet the high fault rating.

Keith

Click to expand...

Except that the fuse block must have an appropriate SCCR itself; not all of them do, especially the cheap ones sold on the internet. The safe bet is to use a fuse and holder from the same mfr. it could be any mfr of an equivalent fuse and holder, I’m just warning against shopping for the lowest price because not all parts are created equal and there are unscrupulous sellers on the internet that don’t know or don’t care.

Side note in confirming kamgenes earlier point; a lot of IEC devices, especially overload relays, require a specific maximum amount of let-through current in order to attain their SCCR because they are somewhat delicate in that regard. So even though an RK-5 fuse might have a higher Interrupt Capacity than a Class CC, that’s not the issue. It’s the Current Limiting effect that they need for the SCCR listing of the entire string of devices.