KLDR is a Littelfuse 600 Vac Class CC time-delay fuse family designed for control transformers, solenoids and similar inductive loads with high magnetizing current. The series is current-limiting, rejection-style and available from 0.1 A to 30 A. Published Littelfuse data lists a 300 Vdc rating and a 200 kA rms symmetrical AC interrupting rating; the exact DC interrupting value must be checked in the datasheet.

KLDR specifications

Class CC and midget 10 x 38 mm fuses are similar in overall size, but Class CC uses rejection geometry and a branch-circuit listing. A generic midget holder or fuse is not an automatic substitute. Use a holder specifically identified for Class CC, such as Bussmann CHCC1DU or Mersen USGCC1.

Model-level KLDR cross-reference examples

Fractional Littelfuse catalog numbers vary by rating; verify the official ordering table before purchase rather than generating a code from the whole-amp pattern.

ATQR vs ATDR: why the distinction matters

All three are Class CC, but their time-current behavior and intended duties differ. Replacing KLDR with ATDR solely because both are marked time-delay can change how the circuit rides through magnetizing current. Compare published curves and confirm the equipment manufacturer's approved fuse type.

Replacement checklist

1. Read the complete KLDR catalog number and convert the amp code carefully.

2. Confirm the installed holder is Class CC and not only a midget 10 x 38 mm holder.

3. Match the exact ampere rating; do not oversize to solve repeated openings without diagnosing the load.

4. Confirm 600 Vac and any required 300 Vdc rating, including the DC interrupting capacity.

5. Compare transformer inrush and time-current curves for KLDR, FNQ-R and ATQR at the selected rating.

6. Recheck coordination, SCCR and equipment listing before final approval.

Frequently Asked Questions

What is the Bussmann equivalent of KLDR010?

FNQ-R-10 is the common 10 A Class CC control-transformer time-delay candidate.

What is the Mersen equivalent of KLDR010?

ATQR10 is the preferred same-function starting candidate. Confirm time-current performance and the application before substitution.

Is KLDR the same as KLKD?

No. KLDR is a UL Class CC rejection-type time-delay fuse. KLKD is a fast-acting midget/supplemental fuse family and is not a direct replacement.

Can KLDR be used for a motor?

KLDR may appear in inductive or control applications, but Littelfuse CCMR is the more direct Class CC motor-oriented family. Select from the actual motor-branch protection requirements.

Does a Class CC fuse fit every 10 x 38 holder?

No. Similar envelope dimensions do not remove the Class CC rejection and listing differences. Use a holder identified for Class CC.

Bottom line

The corrected KLDR cross-reference is KLDR -> FNQ-R -> ATQR for control-transformer time-delay duty. At 10 A, that becomes KLDR010 -> FNQ-R-10 -> ATQR10. Match the exact rating, holder, voltage, curve and listing before installation.

For an exact KLDR fractional or whole-amp model match, send ASBEAM the Littelfuse number and a photo of the fuse and holder. We can check the Bussmann candidate and the appropriate Mersen family.

Technical references

• Littelfuse - KLDR official family datasheet

• Eaton - competitor mapping showing FNQ-R / ATQR / KLDR

• Mersen - ATQR Class CC time-delay