5MF 1.25 Glass Cartridge Fuse Equivalent & Substitute Parts

Part Overview

The 5MF 1.25 is a 1.25 A, 250 V AC/DC fast-blow glass cartridge fuse manufactured by Bel Fuse Inc. in a 5mm x 20mm package format. This part is currently obsolete, with 829 units available in inventory. Due to its discontinued status, identifying equivalent and substitute parts is essential for system maintenance, repair, and redesign applications where this fuse type is specified in legacy equipment or circuit protection requirements.

Substiute Parts

5MF 1.25

Bel Fuse Inc.In Stock: 9165MF 1.25 Datasheet

Current PartRFQ

5MF 1.25-R

Bel Fuse Inc.In Stock: 52005MF 1.25-R Datasheet

DirectRFQ

5SF 1.25-R

Bel Fuse Inc.In Stock: 14825SF 1.25-R Datasheet

Parametric EquivalentRFQ

02171.25TXP

LittelfuseIn Stock: 81702171.25TXP Datasheet

SimilarRFQ

02351.25MXP

Littelfuse Inc.In Stock: 271802351.25MXP Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution for the 5MF 1.25 is determined by the following critical parameters that must remain constant or compatible:

• Current Rating: 1.25 A (exact match required)
• Voltage Rating: 250 V AC (exact match required)
• Package / Case: 5mm x 20mm (physical compatibility with holder)
• Fuse Type: Cartridge, Glass (form factor requirement)
• Response Time: Fast Blow (circuit protection characteristic)
• Mounting Type: Requires Holder (installation method)

Substitute parts are grouped into two categories:

Direct Manufacturer Equivalent (5MF 1.25-R): Identical electrical and mechanical specifications with active product status and improved RoHS compliance.

Parametric Equivalents (5SF 1.25-R, 02171.25TXP, 02351.25MXP): Parts meeting all critical electrical parameters and physical dimensions, manufactured by Bel Fuse Inc. and Littelfuse Inc., with variations in breaking capacity, melting I²t, and regulatory certifications.

Parameter Comparison

Engineering Selection Recommendations

5MF 1.25-R (Bel Fuse Inc.): This is the direct active replacement for the obsolete 5MF 1.25. It maintains identical electrical specifications, breaking capacity, and melting I²t characteristics while offering ROHS3 compliance and significantly higher inventory availability (5157 units). This part is the preferred choice for direct substitution in legacy equipment requiring the original performance profile.

5SF 1.25-R (Bel Fuse Inc.): An active parametric equivalent with identical current, voltage, and package specifications. Breaking capacity is reduced to 35 A, and melting I²t is increased to 2.5. This part carries expanded regulatory certifications including CCC, IMQ, SEMKO, and VDE. Selection of this part requires confirmation that the reduced breaking capacity and altered thermal response are acceptable for the application.

02171.25TXP (Littelfuse, Series 217): An active parametric equivalent with identical electrical ratings and package dimensions. Breaking capacity is 35 A with melting I²t of 2.23. This part offers the broadest regulatory approval scope (BSI, CE, CCC, CSA, KC, PSE, SEMKO, UR, VDE) and is suitable for applications requiring international compliance certifications. Physical dimensions are 5.20mm diameter versus 5.10mm for the original part.

02351.25MXP (Littelfuse Inc., Series 235): An active parametric equivalent meeting all critical electrical parameters. Breaking capacity is 100 A with the lowest melting I²t value of 1.085. This part is appropriate for applications where faster thermal response and higher breaking capacity are beneficial. Physical dimensions are 5.20mm diameter.

Frequently Asked Questions (FAQ)

Q: Can the 5MF 1.25-R be used as a direct replacement for the obsolete 5MF 1.25?

A: Yes. The 5MF 1.25-R is the direct active equivalent, maintaining identical current rating (1.25 A), voltage rating (250 V), breaking capacity (200 A), melting I²t (1.5), and package dimensions (5mm x 20mm). It is the recommended substitution for legacy equipment.

Q: What is the difference between the 5MF 1.25-R and the 5SF 1.25-R?

A: Both are Bel Fuse Inc. products with identical electrical ratings and package size. The 5SF 1.25-R has a lower breaking capacity (35 A versus 200 A) and higher melting I²t (2.5 versus 1.5). The 5SF 1.25-R carries additional international certifications. Selection depends on whether the application requires the higher breaking capacity of the 5MF series.

Q: Are the Littelfuse parts (02171.25TXP and 02351.25MXP) physically compatible with the original fuse holder?

A: Both Littelfuse parts maintain the 5mm x 20mm package specification. However, 02171.25TXP has a diameter of 5.20mm and 02351.25MXP also has a diameter of 5.20mm, compared to 5.10mm for the original 5MF 1.25. Verify holder tolerance specifications before substitution.

Q: Which substitute part has the best regulatory compliance for international applications?

A: The 02171.25TXP (Littelfuse Series 217) carries the most comprehensive regulatory approvals: BSI, CE, CCC, CSA, KC, PSE, SEMKO, UR, and VDE. This part is suitable for applications requiring broad international market compliance.

Q: Does the melting I²t difference between substitute parts affect circuit protection?

A: Yes. Melting I²t determines the thermal response time of the fuse. The 5MF 1.25-R and 02351.25MXP have lower I²t values (1.5 and 1.085 respectively), resulting in faster thermal response. The 5SF 1.25-R and 02171.25TXP have higher I²t values (2.5 and 2.23), resulting in slower thermal response. Selection must align with the circuit protection requirements of the application.

Q: What is the inventory status of each substitute part?

A: 5MF 1.25-R: 5157 units; 5SF 1.25-R: 1459 units; 02171.25TXP: 744 units; 02351.25MXP: 2630 units. All substitute parts are in active production with adequate stock availability.