Equivalent & Substitute Parts for BK/MDL-2-1/2-R Glass Cartridge Fuse

Part Overview

The BK/MDL-2-1/2-R is a 2.5 A, 250 V AC/DC glass cartridge fuse manufactured by Eaton - Electronics Division. This slow-blow fuse is designed for 3AB and 3AG holder compatibility with dimensions of 0.250" diameter by 1.250" length (6.35mm x 31.75mm). The part is currently active in production with 728 pieces in stock. Equivalent and substitute parts are necessary when the primary part becomes unavailable, when alternative certifications are required for specific regional applications, or when design requirements necessitate different electrical characteristics such as breaking capacity or melting I²t values.

Key Parameters

Parameter	Value
Current Rating	2.5 A
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Response Time	Slow Blow
Package / Case	3AB, 3AG, 1/4" x 1-1/4"
Size / Dimension	0.250" Dia x 1.250" L (6.35mm x 31.75mm)
Mounting Type	Requires Holder
Breaking Capacity @ Rated Voltage	100 A
RoHS Status	ROHS3 Compliant
Approval Agencies	CE, CSA, UL

Substitute Part Grouping Explanation

Substitution eligibility for the BK/MDL-2-1/2-R is determined by the following mandatory parameters:

Primary Substitution Criteria:

Current Rating: 2.5 A (exact match required)
Voltage Rating (AC): 250 V (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Response Time: Slow Blow (exact match required)
Package / Case: 3AB, 3AG, 1/4" x 1-1/4" (exact match required)
Size / Dimension: 0.250" Dia x 1.250" L (exact match required)
Mounting Type: Requires Holder (exact match required)

Secondary Compatibility Parameters:

Breaking Capacity @ Rated Voltage: 100 A or higher acceptable
Melting I²t: Values between 48 and 130 acceptable
DC Cold Resistance: 0.081 to 0.1005 Ohms acceptable
Approval Agencies: CE, CSA, UL certifications acceptable

All identified substitute parts meet the primary substitution criteria. Variations in secondary parameters reflect different manufacturer designs while maintaining functional equivalence within the specified electrical and mechanical constraints.

Parameter Comparison

Manufacturer Part Number	Manufacturer	Current Rating (A)	Voltage Rating (V AC)	Response Time	Breaking Capacity (A)	Melting I²t	DC Cold Resistance (Ohms)	RoHS Status	Approval Agencies	Product Status	Inventory (Pcs)
BK/MDL-2-1/2-R	Eaton - Electronics Division	2.5	250	Slow Blow	100	63.1	0.081	ROHS3 Compliant	CE, CSA, UL	Active	728
BK/MDQ-2-1/2	Eaton - Electronics Division	2.5	250	Slow Blow	100	Not Specified	0.1005	RoHS non-compliant	CSA, UL	Active	1048
MDQ-2-1/2	Eaton - Electronics Division	2.5	250	Slow Blow	35	Not Specified	0.1005	Not Specified	CSA, UL	Active	685
0034.3421	SCHURTER Inc.	2.5	250	Slow Blow	35	48	Not Specified	ROHS3 Compliant	CSA	Obsolete	982
031302.5HXP	Littelfuse Inc.	2.5	250	Slow Blow	100	130	0.0811	ROHS3 Compliant	CE, CSA, K-MARK, PSE, UL	Active	1241
031302.5MXP	Littelfuse Inc.	2.5	250	Slow Blow	100	130	0.0811	ROHS3 Compliant	CE, CSA, K-MARK, PSE, UL	Active	9244

Engineering Selection Recommendations

Tier 1 - Direct Equivalents (Preferred):

The Littelfuse parts 031302.5HXP and 031302.5MXP are the primary recommended substitutes. Both parts are manufactured by Littelfuse Inc., series 313, and maintain active product status. These parts match all primary substitution criteria and provide identical breaking capacity (100 A) to the original BK/MDL-2-1/2-R. Both are ROHS3 compliant and hold comprehensive approval certifications including CE, CSA, K-MARK, PSE, and UL. The 031302.5MXP variant has significantly higher inventory availability (9244 pieces) compared to the main part. DC cold resistance values (0.0811 Ohms) are equivalent to the original specification.

Tier 2 - Functional Equivalents (Alternative):

The Eaton BK/MDQ-2-1/2 maintains active status and provides 100 A breaking capacity matching the original part. However, this substitute is RoHS non-compliant and lacks CE certification, limiting its use in applications requiring full regulatory compliance. The part is suitable for legacy systems or applications where RoHS compliance is not mandated.

Tier 3 - Limited Compatibility (Restricted Use):

The Eaton MDQ-2-1/2 and SCHURTER 0034.3421 both feature reduced breaking capacity (35 A) compared to the original 100 A specification. The SCHURTER part is obsolete and should be avoided for new designs. The MDQ-2-1/2 remains active but the lower breaking capacity restricts its application to circuits with lower fault current ratings.

Frequently Asked Questions (FAQ)

Q: Can I use 031302.5MXP as a direct replacement for BK/MDL-2-1/2-R?

A: Yes. The 031302.5MXP meets all primary substitution criteria: 2.5 A current rating, 250 V AC voltage rating, slow-blow response time, glass cartridge type, 3AB/3AG package compatibility, and 0.250" x 1.250" dimensions. Both parts require the same holder type and provide 100 A breaking capacity. The Littelfuse part is ROHS3 compliant and holds CE, CSA, and UL certifications.

Q: What is the difference between 031302.5HXP and 031302.5MXP?

A: Both parts are electrically and mechanically identical. They share the same current rating, voltage rating, breaking capacity, DC cold resistance, and approval certifications. The primary difference is inventory availability, with 031302.5MXP having substantially higher stock levels (9244 pieces versus 1241 pieces).

Q: Why does the MDQ-2-1/2 have a lower breaking capacity?

A: The MDQ-2-1/2 is designed for applications with lower fault current requirements. Its 35 A breaking capacity is suitable for circuits where the maximum available fault current does not exceed this threshold. This part should only be selected when the application circuit design confirms that fault currents remain below 35 A.

Q: Is the BK/MDQ-2-1/2 suitable for RoHS-compliant applications?

A: No. The BK/MDQ-2-1/2 is marked as RoHS non-compliant. For applications requiring RoHS compliance, select either 031302.5HXP, 031302.5MXP, or the original BK/MDL-2-1/2-R, all of which are ROHS3 compliant.

Q: Can I use the SCHURTER 0034.3421 in new designs?

A: The SCHURTER 0034.3421 is obsolete and should not be specified for new designs. While it meets the primary substitution criteria and is ROHS3 compliant, its obsolete status creates supply chain risk. The Littelfuse alternatives (031302.5HXP or 031302.5MXP) are preferred for all new applications.

Q: What certifications are required for my application?

A: Certification requirements depend on your end-use application and regional regulations. The original BK/MDL-2-1/2-R holds CE, CSA, and UL certifications. The Littelfuse substitutes (031302.5HXP and 031302.5MXP) provide additional certifications including K-MARK and PSE, offering broader regional compliance coverage. Verify your specific application requirements before final part selection.

Q: Are there any differences in operating temperature ranges?

A: The original BK/MDL-2-1/2-R does not specify an operating temperature range. The Littelfuse substitutes (031302.5HXP and 031302.5MXP) are rated for -55°C to 125°C operation. The SCHURTER 0034.3421 is also rated for -55°C to 125°C. For applications requiring operation outside standard temperature ranges, confirm compatibility with the selected substitute part's temperature specification.

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