BK/EFF-1.25 Equivalent & Substitute Parts Reference

Part Overview

The BK/EFF-1.25 is a 1.25 A, 250 V AC/DC board mount radial fuse manufactured by Eaton - Electronics Division. This through-hole component features fast-blow response characteristics and is designed for radial, can-style vertical mounting on printed circuit boards. The part carries obsolete product status, making equivalent and substitute parts necessary for ongoing design support, maintenance, and production continuity. Active equivalent parts from both Eaton and alternative manufacturers provide functional compatibility while maintaining electrical and mechanical specifications.

Substiute Parts

BK/EFF-1.25

Eaton - Electronics DivisionIn Stock: 1227BK/EFF-1.25 Datasheet

Current PartRFQ

SR-5F-1.25A-BK

Eaton - Electronics DivisionIn Stock: 1042SR-5F-1.25A-BK Datasheet

SimilarRFQ

MRF 1.25-AMMO

Bel Fuse Inc.In Stock: 1231MRF 1.25-AMMO Datasheet

DirectRFQ

MRF 1.25-BULK

Bel Fuse Inc.In Stock: 2459MRF 1.25-BULK Datasheet

DirectRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the BK/EFF-1.25 is determined by strict alignment of the following electrical and mechanical parameters:

Critical Matching Parameters:

• Current Rating: 1.25 A (exact match required)
• Voltage Rating (AC): 250 V (exact match required)
• Response Time: Fast Blow (exact match required)
• Mounting Type: Through Hole (exact match required)
• Package / Case: Radial, Can, Vertical (exact match required)

Acceptable Variation Parameters:

• Size / Dimension: Tolerance within 0.006" (0.15mm) diameter and height variation
• Breaking Capacity @ Rated Voltage: Minimum 35 A acceptable
• Melting I²t: Range 0.61 to 4.4 acceptable
• DC Cold Resistance: Range 0.043 to 0.116 Ohms acceptable
• Operating Temperature Range: Minimum -40°C to 125°C acceptable

All three substitute parts meet these criteria and are qualified for direct replacement in applications requiring the BK/EFF-1.25 electrical and mechanical interface.

Parameter Comparison

Engineering Selection Recommendations

SR-5F-1.25A-BK (Eaton - Electronics Division)

This substitute maintains manufacturer continuity with the original BK/EFF-1.25 part. Both are Eaton products within the same product family. The SR-5F series is active and carries cULus and PSE certifications. Physical dimensions show minor variation (0.335" Dia x 0.319" H versus 0.329" Dia x 0.303" H), remaining within acceptable tolerance for radial through-hole mounting. The higher melting I²t value (4.4 versus 0.61) indicates slightly different thermal response characteristics but remains within the fast-blow classification. Operating temperature minimum is -40°C versus -55°C on the original part. Select this substitute when maintaining single-manufacturer sourcing is a design requirement.

MRF 1.25-AMMO (Bel Fuse Inc.)

This substitute from Bel Fuse Inc. provides the most comprehensive certification coverage, including AEC-Q200, CE, CSA, cULus, PSE, SEMKO, and VDE approvals. Physical dimensions match the original part exactly (0.329" Dia x 0.303" H). The part is ROHS3 compliant and REACH unaffected. Breaking capacity is 35 A versus 50 A on the original, and melting I²t is 1.3 versus 0.61. Packaging is Tape & Box (TB) format. Select this substitute for applications requiring automotive-grade qualification (AEC-Q200) or when comprehensive international certifications are mandatory.

MRF 1.25-BULK (Bel Fuse Inc.)

This substitute is functionally identical to MRF 1.25-AMMO with the same electrical specifications, certifications, and compliance status. The primary difference is bulk packaging format rather than Tape & Box. Physical dimensions match the original part exactly. Highest inventory availability (2365 Pcs) supports production continuity. Select this substitute for high-volume applications or when bulk packaging reduces component handling costs.

Frequently Asked Questions (FAQ)

Q: Can SR-5F-1.25A-BK be used as a direct replacement for BK/EFF-1.25 on existing PCBs?

A: Yes. Both parts share identical electrical ratings (1.25 A, 250 V AC, fast-blow response) and through-hole radial mounting. Physical dimensions vary by 0.006" in diameter and 0.016" in height, which remains within acceptable tolerance for radial component footprints. Verify PCB pad spacing accommodates the slightly larger SR-5F case before production implementation.

Q: What is the difference between MRF 1.25-AMMO and MRF 1.25-BULK?

A: Both parts are electrically and mechanically identical. MRF 1.25-AMMO is packaged in Tape & Box (TB) format, while MRF 1.25-BULK uses bulk packaging. Select based on production volume and handling requirements. Bulk packaging typically reduces per-unit cost for high-volume applications.

Q: Why does MRF 1.25-AMMO have lower breaking capacity (35 A) than the original BK/EFF-1.25 (50 A)?

A: Breaking capacity is a rated specification that differs between manufacturers based on design and testing standards. Both parts meet the 1.25 A current rating and fast-blow response requirement. Verify that 35 A breaking capacity is acceptable for your circuit protection application. If higher breaking capacity is required, the SR-5F-1.25A-BK (50 A) or original BK/EFF-1.25 specification should be maintained.

Q: Are MRF 1.25-AMMO and MRF 1.25-BULK suitable for automotive applications?

A: Yes. Both MRF parts carry AEC-Q200 certification, qualifying them for automotive-grade component applications. They are also ROHS3 compliant and REACH unaffected, meeting automotive supply chain requirements.

Q: What is the operating temperature difference between BK/EFF-1.25 and SR-5F-1.25A-BK?

A: BK/EFF-1.25 operates from -55°C to 125°C, while SR-5F-1.25A-BK operates from -40°C to 125°C. The SR-5F has a higher minimum operating temperature by 15°C. For applications requiring operation below -40°C, use BK/EFF-1.25, MRF 1.25-AMMO, or MRF 1.25-BULK, all rated to -55°C.

Q: Can these substitute parts be mixed in the same production batch?

A: All three substitutes meet the same electrical and mechanical interface requirements. However, mixing different manufacturers or series in a single production batch may complicate traceability and quality documentation. Establish a single approved substitute part for each design revision to maintain consistency.