Cartridge Fuse differences

[Jerry Ryan]

I've got a 2013 Ram 2500.
Blew a 20a cartridge fuse today for trailer parking lights. After finding short in trailer wiring, I found another 20a cartridge fuse on an unused circuit but didn't look the same. Tried it & it worked. Then I started thinking I probably should have enough spare fuses in my toolbox just in case...but that's where I get confused.

As far as the cartridge fuses, can someone explain the difference between Mcase, Jcase, FMM, and FMX fuses and if they can be used interchangeable??? Does Littlefuse make some & Buss the other?

 

[gsbrockman]

I've got a 2013 Ram 2500.
Blew a 20a cartridge fuse today for trailer parking lights. After finding short in trailer wiring, I found another 20a cartridge fuse on an unused circuit but didn't look the same. Tried it & it worked. Then I started thinking I probably should have enough spare fuses in my toolbox just in case...but that's where I get confused.

As far as the cartridge fuses, can someone explain the difference between Mcase, Jcase, FMM, and FMX fuses and if they can be used interchangeable??? Does Littlefuse make some & Buss the other?

I cannot answer the difference between the fuses, but I am fairly sure it has to do with external size mostly.

In any event.....this link https://www.turbodieselregister.com...tyle-pdc-fuses-available.249938/#post-2414949 might help in sourcing a good fuse kit.

 

[Timd32]

Someone else can correct any of this, but we are a Mersen fuse supplier, old ferrez shawmut line, deal with industrial fuses and the sort 480vac to 38kvac, but I looked up some of this stuff here is what I came across.

Littlefuse Brand= mcase, jcase
Buss= fmx, fmm

FMX and Jcase the same

Mcase is a patented littlefuse I dont know of or see a cross reference for those.

Mcase is a time delay fuse 2.8mm blades 15A to 40A. Its referred to as a middle range cartridge fuse.

Jcase/FMX is a time delay fuse 5.5mm blades 20A to 60A, 27mm tall.

There is a low profile Jcase/FMX that is only 16mm tall.

FMM is time delay fuse 15mm tall latest version little smaller then Jcase/fmx, the footprint they show would not lend them to be interchange able, there is a cross reference to a FMM, but plugging in the numbers did not easily come across that part. So Bussman might be preferred on those.

There are tons of small kits out there, littlefuse also has a sample program where you can order.

I'm alwasy amazed at the ampacity of these little things compared to say a industrial fuse. But the KAIC rating of a industrial fuse being 200kA (200,000A) its not quite a fair comparison.

The I2T rating which is what shows the inrush for larger loads is pretty impressive as well looking at the technical sheet.

FMX can replace a fusibile link they make some neat retrofit bases as well for that purpose from what I found.

 

[Jerry Ryan]

Someone else can correct any of this, but we are a Mersen fuse supplier, old ferrez shawmut line, deal with industrial fuses and the sort 480vac to 38kvac, but I looked up some of this stuff here is what I came across.

Littlefuse Brand= mcase, jcase
Buss= fmx, fmm

FMX and Jcase the same

Mcase is a patented littlefuse I dont know of or see a cross reference for those.

Mcase is a time delay fuse 2.8mm blades 15A to 40A. Its referred to as a middle range cartridge fuse.

Jcase/FMX is a time delay fuse 5.5mm blades 20A to 60A, 27mm tall.

There is a low profile Jcase/FMX that is only 16mm tall.

FMM is time delay fuse 15mm tall latest version little smaller then Jcase/fmx, the footprint they show would not lend them to be interchange able, there is a cross reference to a FMM, but plugging in the numbers did not easily come across that part. So Bussman might be preferred on those.

There are tons of small kits out there, littlefuse also has a sample program where you can order.

I'm alwasy amazed at the ampacity of these little things compared to say a industrial fuse. But the KAIC rating of a industrial fuse being 200kA (200,000A) its not quite a fair comparison.

The I2T rating which is what shows the inrush for larger loads is pretty impressive as well looking at the technical sheet.

FMX can replace a fusibile link they make some neat retrofit bases as well for that purpose from what I found.

Excellent! That's what I was looking for. Thanks!

 

[SnoKing]

Here is a earlier thread on fuses. The fuses in my list in the thread have been riding along for three years and 47K

https://www.turbodieselregister.com/threads/fuses-for-our-new-trucks.246050/page-3#post-2454464