BK/MDL-1/4 Equivalent & Substitute Parts

Part Overview

The BK/MDL-1/4 is a 250 mA, 250 V AC/DC slow-blow glass cartridge fuse in 3AB/3AG form factor (1/4" x 1-1/4"). This component requires a compatible fuse holder for installation and is rated for 35 A breaking capacity at rated voltage. The part is classified as obsolete, necessitating identification of active equivalent alternatives that maintain identical electrical and mechanical specifications for direct substitution in existing applications.

Key Parameters

Parameter	Value
Current Rating	250 mA
Voltage Rating (AC)	250 V
Response Time	Slow Blow
Fuse Type	Cartridge, Glass
Package / Case	3AB, 3AG, 1/4" x 1-1/4"
Size / Dimension	0.250" Dia x 1.250" L (6.35mm x 31.75mm)
Breaking Capacity @ Rated Voltage	35 A
Mounting Type	Requires Holder

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following critical parameters: current rating (250 mA), voltage rating (250 V AC), response time (slow blow), fuse type (cartridge glass), physical dimensions (0.250" Dia x 1.250" L), and package designation (3AB, 3AG). All substitute parts listed maintain these specifications without deviation.

Substitute parts are grouped into two categories:

Direct Manufacturer Equivalents (Eaton - Electronics Division): Parts BK/MDL-1/4-R and MDL-1/4-R are direct successors to the obsolete BK/MDL-1/4, differing only in product status (active) and compliance certifications. BK/MDL-1/4VX-R is a parametric equivalent within the same manufacturer series.

Cross-Manufacturer Parametric Equivalents: Parts from Littelfuse Inc. (0313.250HXP, 0313.250MXP, 0313.250VXP) and SCHURTER Inc. (0034.3411) meet all electrical and mechanical specifications. These parts are sourced from alternative manufacturers and maintain compatibility with 3AB/3AG fuse holders.

Parameter Comparison

Part Number	Manufacturer	Current Rating (mA)	Voltage (V AC)	Response Time	Package	Breaking Capacity (A)	Product Status	RoHS Status
BK/MDL-1/4	Eaton	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Obsolete	Non-compliant
BK/MDL-1/4-R	Eaton	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Active	ROHS3 Compliant
MDL-1/4-R	Eaton	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Active	RoHS Compliant
BK/MDL-1/4VX-R	Eaton	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Active	RoHS Compliant
BK/MDQ-1/4	Eaton	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Active	Non-compliant
MDQ-1/4	Eaton	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Active	Not specified
0034.3411	SCHURTER	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Obsolete	ROHS3 Compliant
0313.250HXP	Littelfuse	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Active	ROHS3 Compliant
0313.250MXP	Littelfuse	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Active	ROHS3 Compliant
0313.250VXP	Littelfuse	250	250	Slow Blow	3AB, 3AG, 1/4" x 1-1/4"	35	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: BK/MDL-1/4-R or MDL-1/4-R (Eaton - Electronics Division)

These parts are direct successors to the obsolete BK/MDL-1/4 from the same manufacturer. Both maintain identical electrical and mechanical specifications. BK/MDL-1/4-R carries ROHS3 compliance and CE certification in addition to CSA and UL approvals. MDL-1/4-R is RoHS compliant with CSA and UL approvals. Both are in active production status with substantial inventory availability.

Secondary Recommendation: 0313.250HXP, 0313.250MXP, or 0313.250VXP (Littelfuse Inc.)

These Littelfuse 313 series parts meet all electrical and mechanical requirements and are ROHS3 compliant with CE, CSA, and UL certifications. All three variants are in active production. Selection among these three variants depends on specific application requirements not differentiated by the provided parameters.

Alternative Recommendation: BK/MDL-1/4VX-R (Eaton - Electronics Division)

This parametric equivalent maintains all critical specifications and is in active production with RoHS compliance and CSA/UL certifications.

Not Recommended for New Designs: BK/MDQ-1/4, MDQ-1/4, and 0034.3411

While these parts meet electrical and mechanical specifications, BK/MDQ-1/4 and MDQ-1/4 lack RoHS3 compliance documentation, and 0034.3411 is classified as obsolete. These parts are suitable only for legacy system maintenance where original part compatibility is required.

Frequently Asked Questions (FAQ)

Q: Can BK/MDL-1/4-R be used as a direct replacement for BK/MDL-1/4?

A: Yes. BK/MDL-1/4-R is the active production equivalent of the obsolete BK/MDL-1/4. Both parts share identical electrical ratings (250 mA, 250 V AC), response time (slow blow), physical dimensions (0.250" Dia x 1.250" L), and package designation (3AB, 3AG). The parts are mechanically and electrically interchangeable in any application using 3AB/3AG fuse holders.

Q: What is the difference between BK/MDL-1/4-R and MDL-1/4-R?

A: Both parts are Eaton equivalents with identical electrical and mechanical specifications. BK/MDL-1/4-R carries ROHS3 compliance and CE certification. MDL-1/4-R is RoHS compliant with CSA and UL certifications. Selection depends on regulatory requirements for the target application.

Q: Are Littelfuse 0313.250HXP, 0313.250MXP, and 0313.250VXP interchangeable with BK/MDL-1/4?

A: Yes. All three Littelfuse parts meet the electrical specifications (250 mA, 250 V AC, slow blow) and physical dimensions (0.250" Dia x 1.250" L) required for 3AB/3AG fuse holder compatibility. All are ROHS3 compliant with CE, CSA, and UL certifications. The parts are parametric equivalents suitable for direct substitution.

Q: Can I use BK/MDQ-1/4 or MDQ-1/4 as replacements?

A: These parts meet all electrical and mechanical specifications and are in active production. However, BK/MDQ-1/4 and MDQ-1/4 lack documented RoHS3 compliance. Use these parts only in applications where RoHS compliance is not required or where legacy part compatibility is mandated.

Q: What fuse holder types are compatible with these parts?

A: All listed parts require a 3AB or 3AG fuse holder. The physical dimensions (0.250" Dia x 1.250" L / 6.35mm x 31.75mm) are standardized across all substitute parts and are compatible with any holder rated for these form factors.

Q: Are there any differences in DC cold resistance among the substitute parts?

A: Yes. DC cold resistance varies: BK/MDL-1/4 and BK/MDL-1/4-R measure 3.2–3.208 Ohms, while BK/MDQ-1/4 and MDQ-1/4 measure 5.775 Ohms. Littelfuse parts (0313.250HXP, 0313.250MXP, 0313.250VXP) measure 4.27 Ohms. These differences do not affect fuse operation in standard applications but should be considered in circuits sensitive to resistance variations.

Q: What is the melting I²t specification, and does it vary among substitutes?

A: Melting I²t represents the thermal energy required to melt the fuse element. Eaton MDL series parts specify 0.447, Littelfuse 313 series parts specify 0.385, and SCHURTER 0034.3411 specifies 0.4. These variations are within acceptable tolerance for slow-blow fuse operation and do not preclude substitution in standard applications.

Q: Which substitute part has the best regulatory compliance?

A: Littelfuse 0313.250HXP, 0313.250MXP, and 0313.250VXP all carry ROHS3 compliance, CE certification, and CSA/UL approvals. BK/MDL-1/4-R also carries ROHS3 compliance with CE, CSA, and UL certifications. These parts are suitable for applications with stringent regulatory requirements.

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