BK/EFF-2 Board Mount Fuse 2A 250VAC Equivalent & Substitute Parts

Part Overview

The BK/EFF-2 is a 2 A 250 V AC/DC board mount fuse with radial, can, vertical package configuration manufactured by Eaton - Electronics Division. This component is classified as obsolete, necessitating identification of active equivalent and substitute parts for ongoing design support and procurement. The fuse features fast-blow response characteristics suitable for circuit protection applications requiring rapid fault interruption at rated voltage conditions.

Key Parameters

Parameter	Value
Current Rating	2 A
Voltage Rating (AC)	250 V
Response Time	Fast Blow
Mounting Type	Through Hole
Package / Case	Radial, Can, Vertical
Fuse Type	Board Mount (Cartridge Style Excluded)
Breaking Capacity @ Rated Voltage	50 A
Operating Temperature Range	-55°C ~ 125°C
Size / Dimension	0.329" Dia x 0.303" H (8.35mm x 7.70mm)

Substitute Part Grouping Explanation

Substitution eligibility for the BK/EFF-2 is determined by strict equivalence across the following critical parameters:

Mandatory Matching Parameters:

Current Rating: 2 A
Voltage Rating (AC): 250 V
Response Time: Fast Blow
Mounting Type: Through Hole
Fuse Type: Board Mount (Cartridge Style Excluded)
Package / Case: Radial, Can, Vertical

Allowable Variation Parameters:

Breaking Capacity @ Rated Voltage: 35 A to 50 A (all substitutes meet or exceed minimum protection requirements)
Operating Temperature Range: Minimum -40°C to -55°C; Maximum 85°C to 125°C (all substitutes cover or exceed the original operating envelope)
Physical Dimensions: Tolerance within 0.006" diameter and 0.016" height (maintains PCB footprint compatibility)
DC Cold Resistance: 0.026 Ohms to 0.058 Ohms (minor variations acceptable within thermal design margins)
Melting I²t: 0.63 to 9 (all values within acceptable thermal response envelope)

All identified substitutes maintain electrical and mechanical compatibility with the original BK/EFF-2 specification.

Parameter Comparison

Parameter	BK/EFF-2 (Eaton)	SR-5F-2A-BK (Eaton)	MRF 2-AMMO (Bel Fuse)	37312000410 (Littelfuse)	MRF 2-BULK (Bel Fuse)
Current Rating (Amps)	2 A	2 A	2 A	2 A	2 A
Voltage Rating - AC	250 V	250 V	250 V	250 V	250 V
Response Time	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	Radial, Can, Vertical	Radial, Can, Vertical	Radial, Can, Vertical	Radial, Can, Vertical	Radial, Can, Vertical
Breaking Capacity @ Rated Voltage	50 A	50 A	35 A	50 A	35 A
Operating Temperature Range	-55°C ~ 125°C	-40°C ~ 125°C	-55°C ~ 125°C	-40°C ~ 85°C	-55°C ~ 125°C
Size / Dimension	0.329" Dia x 0.303" H (8.35mm x 7.70mm)	0.335" Dia x 0.319" H (8.50mm x 8.10mm)	0.329" Dia x 0.303" H (8.35mm x 7.70mm)	0.335" Dia x 0.315" H (8.50mm x 8.00mm)	0.329" Dia x 0.303" H (8.35mm x 7.70mm)
DC Cold Resistance (Ohms)	0.026	0.058	0.028	0.03857	0.028
Melting I²t	1.8	9	2.1	0.63	2.1
Product Status	Obsolete	Active	Active	Active	Active
RoHS Status	Not Specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Primary Substitute - SR-5F-2A-BK (Eaton - Electronics Division): Active product status with identical electrical ratings and fast-blow response. Maintains Eaton manufacturer continuity. Approval agencies include cULus and PSE. Operating temperature range of -40°C to 125°C covers the majority of industrial applications. Slight dimensional increase (0.335" Dia x 0.319" H) remains within PCB footprint tolerance. Higher melting I²t value (9) provides extended thermal response margin. ROHS3 compliant. Bulk packaging available.

Secondary Substitute - MRF 2-AMMO or MRF 2-BULK (Bel Fuse Inc.): Active product status with identical electrical ratings and fast-blow response. Exact dimensional match to original BK/EFF-2 (0.329" Dia x 0.303" H) ensures direct PCB compatibility without layout modification. Operating temperature range -55°C to 125°C matches original specification. Breaking capacity of 35 A meets minimum protection requirements. Comprehensive approval certifications include AEC-Q200, CE, CSA, cULus, PSE, SEMKO, and VDE. ROHS3 compliant. MRF 2-AMMO supplied in Tape & Box packaging; MRF 2-BULK supplied in bulk packaging.

Tertiary Substitute - 37312000410 (Littelfuse Inc., TR5® 373 Series): Active product status with identical electrical ratings and fast-blow response. Littelfuse TR5® 373 series represents established industrial standard. Breaking capacity of 50 A matches original specification. CSA and cULus approvals. ROHS3 compliant. Operating temperature range of -40°C to 85°C is narrower than original; suitable for applications not requiring -55°C lower temperature operation. Slight dimensional increase (0.335" Dia x 0.315" H) remains within tolerance. Lowest melting I²t value (0.63) provides fastest thermal response. Bulk packaging available.

Frequently Asked Questions (FAQ)

Q: Can SR-5F-2A-BK be used as a direct replacement for BK/EFF-2 without PCB modification?

A: SR-5F-2A-BK maintains electrical equivalence across all critical parameters. Physical dimensions increase from 0.329" to 0.335" diameter and 0.303" to 0.319" height. This variation remains within standard PCB footprint tolerance for radial through-hole components. No PCB modification is required for standard board designs.

Q: What is the difference between MRF 2-AMMO and MRF 2-BULK?

A: Both MRF 2-AMMO and MRF 2-BULK are electrically and mechanically identical. The difference is packaging: MRF 2-AMMO is supplied in Tape & Box (TB) format for automated assembly; MRF 2-BULK is supplied in bulk format for manual assembly or reel conversion. Electrical performance and specifications are identical.

Q: Why does 37312000410 have a lower melting I²t value (0.63) compared to other substitutes?

A: Melting I²t represents the thermal energy required to melt the fuse element. Lower I²t values indicate faster thermal response to overcurrent conditions. The 37312000410 provides the fastest response among available substitutes while maintaining the 2 A current rating and 250 V voltage rating. Selection depends on specific circuit protection requirements.

Q: Are all substitutes ROHS3 compliant?

A: Yes. SR-5F-2A-BK, MRF 2-AMMO, MRF 2-BULK, and 37312000410 are all ROHS3 compliant. The original BK/EFF-2 RoHS status was not specified in available documentation.

Q: Which substitute has the widest operating temperature range?

A: MRF 2-AMMO and MRF 2-BULK both support -55°C to 125°C operating temperature range, matching the original BK/EFF-2 specification. SR-5F-2A-BK supports -40°C to 125°C. The 37312000410 supports -40°C to 85°C, which is the narrowest range among active substitutes.

Q: What approval agencies are common across all substitutes?

A: CSA and cULus certifications are present across all four active substitutes. MRF 2-AMMO and MRF 2-BULK additionally carry AEC-Q200, CE, PSE, SEMKO, and VDE approvals, providing the broadest regulatory coverage.

Q: Can dimensional differences affect PCB assembly?

A: Dimensional variations between substitutes remain within standard PCB footprint tolerance for radial through-hole fuses. MRF 2-AMMO and MRF 2-BULK maintain exact dimensional match to BK/EFF-2 (0.329" Dia x 0.303" H). SR-5F-2A-BK and 37312000410 increase to 0.335" diameter and approximately 0.315-0.319" height. These variations do not require PCB redesign for standard board layouts with conventional component spacing.

Request Quote (Ships tomorrow)

Part Number

Quantity

Company

Contact Name

E-mail

Message