Type J fuse vs RK5 Fuse

[fifty60]

Both of these fuses are dual element-time delay fuses. Can anyone suggest why I would use one type of fuse instead of the other?

I typically always use the LPJ fuses, but all I have availaible is a disconnect that accepts only the RK5.

The equipment has refrigeration compressors and heaters...would the RK5's be acceptable?

 

[petersonra]

does not really matter much in most applications.

 

[Jraef]

There is a difference, but it likely doesn't matter that much. The Class J isn't necessarily the issue, because you can get a Class J fuse that is not time delay too, which would be inappropriate for a motor load. But that said, this PARTICULAR fuse (LPJ) is rated 300kAIC, whereas an equivalent RK5 (FRS) fuse would be rated 200kAIC. The likelihood that you will have anything even close to 50kA available at a refrigeration compressor motor are so slim that I wouldn't worry about it though.

Mostly it comes down to physical size vs cost / and sometimes current limitation / let through. Class J fuses in larger sizes tend to be more compact, which makes them good for when real estate is at a premium, but they cost more because with a shorter distance, they are more highly engineered and use more expensive materials in order to attain the performance. So if you are a high volume OEM, you kind of have to want them to be willing to pay extra. For the occasional user, the difference in price doesn't matter as much.

 

[petersonra]

Mostly it comes down to physical size vs cost / and sometimes current limitation / let through. Class J fuses in larger sizes tend to be more compact, which makes them good for when real estate is at a premium, but they cost more because with a shorter distance, they are more highly engineered and use more expensive materials in order to attain the performance. So if you are a high volume OEM, you kind of have to want them to be willing to pay extra. For the occasional user, the difference in price doesn't matter as much.

oddly, our price for class J fuses is less than for RK5 fuses. fuse holders are less as well.

at least for 200A and smaller.

 

[fifty60]

The disconnects I use come with the J-Clips fitted, or otherwise they have to use the FRS fuses. First time i have had to use the FRS's. I needed a 30A with a J-clip but to get the clip fitted from the factory could not get started since they are on vacation until the 5th of january, so I went with the non-j clip version. Funny when the rep told me that the factory (Eaton) was on vacation until the 5th of january i instantly thought that they must be from Europe, tis the season :slaphead:
I will compare the sizes when they come in, as well as the cost. I will be extremely suprised if they come in cheaper than the LPJ's, mainly since we specifically order them with the J-clips. For no real gain (we state a 5KVA SCCR, so the 300KAIC is not much help) I will be suprised if we were paying more for them to put in the J-clips since they have to be "customized" to install the clips.

 

[petersonra]

another option would be to just remove the fuse clips and use it as an unfused switch and install some din rail mounted fuse blocks downstream. class cc fuses and fuse blocks (30 A and smaller) can be had for less than $20/pole). Class J fuse blocks and fuses are a little more, maybe still less then $20/pole.