Littelfuse, Eaton Bussmann and Mersen manufacture many products to the same UL fuse classes. That makes three-brand sourcing possible, but it does not make every same-class fuse identical. Cross-reference by class and functional characteristic first, then compare the exact catalog number.

Three-brand series matrix

Exact model examples

Littelfuse catalog syntax commonly pads whole-amp values with zeros: KLDR010 is 10 A, KLDR005 is 5 A, JTD030 is 30 A and JLS100 is 100 A. Fractional values use a different code pattern, so do not create a part number by guessing. Verify the published ordering table.

How to choose between KLDR and CCMR

• Use KLDR as the starting family for control transformers, solenoids and inductive devices with high magnetizing current. Compare with FNQ-R and ATQR.

• Use CCMR as the starting family for compact motor-branch or general time-delay protection. Compare with LP-CC and ATDR.

• Use KLKR when a fast-acting Class CC response is required. Compare with KTK-R and ATMR.

• Do not replace KLDR with KLKR merely because the ampere and voltage ratings match; the time-current behavior changes.

Cross-reference approval checklist

1. Confirm the complete Littelfuse catalog number and whether an indicating suffix is present.

2. Match UL class and holder rejection geometry.

3. Match speed and functional family, not just the generic label 'time-delay.'

4. Confirm AC and DC voltage ratings and interrupting ratings independently.

5. Compare time-current curves and let-through data where equipment damage or selectivity depends on them.

6. Confirm the replacement is allowed by the machine, panel or listed assembly documentation.

Frequently Asked Questions

What does KLDR010 cross to?

The usual same-function candidates are Bussmann FNQ-R-10 and Mersen ATQR10. All three are Class CC control-transformer-oriented time-delay families; verify the exact time-current and DC requirements.

Is JLS a time-delay Class J fuse?

No. Littelfuse JLS is fast-acting. Littelfuse JTD and JTD_ID are time-delay Class J families.

What is the Bussmann equivalent of JTD030?

LPJ-30SP is the common 30 A Class J time-delay candidate. If visual indication is required, compare the applicable indicating variants as well.

Can I use KLKD instead of KLKR?

KLKD is a midget/supplemental family, while KLKR is UL Class CC with rejection features and branch-circuit ratings. The holder, listing and protection role must be checked.

Bottom line

Use a three-step hierarchy: UL class, functional speed/family, then exact rating and curve. For common model searches, KLDR010 -> FNQ-R-10 / ATQR10, CCMR010 -> LP-CC-10 / ATDR10, and JTD030 -> LPJ-30SP / AJT30 are useful starting points.

ASBEAM can review Littelfuse, Bussmann and Mersen candidates from a nameplate photo or BOM. Include the load type and holder model so the result is more than a series-name match.

Technical references

• Littelfuse - KLDR Class CC time-delay datasheet

• Littelfuse - KLKR Class CC fast-acting datasheet

• Littelfuse - JTD Class J time-delay family

• Littelfuse - JLS Class J fast-acting family