Equivalent & Substitute Parts for 5SF 1.25-R Glass Cartridge Fuse

Part Overview

The 5SF 1.25-R is a fast-blow glass cartridge fuse manufactured by Bel Fuse Inc., rated for 1.25 A at 250 V AC/DC with a 5mm x 20mm form factor. This component is actively produced and widely used in industrial and commercial electrical protection circuits. Equivalent and substitute parts are necessary when the primary part is unavailable, when alternative certifications are required for specific markets, or when design requirements necessitate different electrical characteristics within the same functional category.

Substiute Parts

5SF 1.25-R

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

Current PartRFQ

5MF 1.25-R

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

Parametric EquivalentRFQ

0034.1517

SCHURTER Inc.In Stock: 20480034.1517 Datasheet

DirectRFQ

02171.25HXP

Littelfuse Inc.In Stock: 152802171.25HXP Datasheet

DirectRFQ

02171.25MXP

Littelfuse Inc.In Stock: 510902171.25MXP Datasheet

DirectRFQ

02171.25VXP

Littelfuse Inc.In Stock: 91702171.25VXP Datasheet

DirectRFQ

BK/S500-1.25-R

Eaton - Electronics DivisionIn Stock: 860BK/S500-1.25-R Datasheet

DirectRFQ

02351.25MXP

Littelfuse Inc.In Stock: 271802351.25MXP Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the 5SF 1.25-R is determined by strict adherence to the following parameters:

Critical Parameters (Must Match Exactly):

• Current Rating: 1.25 A
• Voltage Rating (AC): 250 V
• Fuse Type: Cartridge, Glass
• Response Time: Fast Blow
• Package / Case: 5mm x 20mm
• Mounting Type: Requires Holder

Allowable Variation Parameters:

• Breaking Capacity @ Rated Voltage: May vary (35 A to 200 A)
• Melting I²t: May vary (0.84 to 2.5)
• DC Cold Resistance: May vary (0.062 Ω to 0.1055 Ω)
• Approval Agency certifications: May differ by market region
• Manufacturer: Different manufacturers acceptable

All substitute parts listed below meet the critical parameters. Variations in breaking capacity, melting I²t, and DC cold resistance reflect different manufacturer designs while maintaining functional equivalence for the 1.25 A, 250 V, 5x20mm cartridge fuse category.

Parameter Comparison

Engineering Selection Recommendations

Direct Equivalents (Identical Breaking Capacity and Similar Melting I²t):

• 02171.25HXP, 02171.25MXP, 02171.25VXP (Littelfuse 217 series) and 0034.1517 (SCHURTER FSF 5x20) are direct functional equivalents with breaking capacity of 35 A and melting I²t values within 1.81 to 2.23, closely matching the 5SF 1.25-R specification of 2.5. These parts carry comprehensive international certifications including CCC, CE, CSA, and VDE, suitable for global applications.

Higher Breaking Capacity Alternative:

• 5MF 1.25-R (Bel Fuse Inc.) provides 200 A breaking capacity with lower melting I²t of 1.5. This part is appropriate when higher fault current withstand capability is required, though it carries fewer certifications (CE, CSA, cULus, PSE).

Lower Melting I²t Alternative:

• BK/S500-1.25-R (Eaton S500 series) offers the lowest melting I²t at 0.84, providing faster response characteristics. This part is suitable for applications requiring enhanced sensitivity to overcurrent conditions.

Reduced Certification Alternative:

• 02351.25MXP (Littelfuse 235 series) carries fewer certifications (CE, CSA, KC, PSE, UL) and higher breaking capacity of 100 A with lower melting I²t of 1.085. Selection of this part should be based on specific regional certification requirements.

All substitute parts maintain active product status and ROHS3 compliance. Selection should be based on required certifications for the target market, breaking capacity requirements, and response time characteristics needed for the application.

Frequently Asked Questions (FAQ)

Q: Can I substitute the 5SF 1.25-R with any of these parts without circuit modification?

A: Yes, all listed substitute parts maintain identical current rating (1.25 A), voltage rating (250 V AC), fuse type (cartridge glass), response time (fast blow), and physical package (5mm x 20mm). No circuit modification is required. However, differences in breaking capacity and melting I²t may affect performance under fault conditions, so application-specific requirements should be verified.

Q: What is the difference between the Littelfuse 217 series variants (02171.25HXP, 02171.25MXP, 02171.25VXP)?

A: All three Littelfuse 217 series parts are electrically and mechanically identical, with identical current rating, voltage rating, breaking capacity (35 A), melting I²t (2.23), and DC cold resistance (0.0701 Ω). The suffix designations (HXP, MXP, VXP) represent different packaging or distribution channel variants. They are interchangeable for engineering purposes.

Q: Why does the 5MF 1.25-R have a higher breaking capacity (200 A) than the 5SF 1.25-R (35 A)?

A: Breaking capacity is a design characteristic that reflects the fuse's ability to safely interrupt fault currents without rupturing. The 5MF series is engineered for higher fault current environments while maintaining the same 1.25 A nominal current rating. Selection between these parts depends on the maximum fault current expected in the circuit.

Q: Are all substitute parts ROHS3 compliant?

A: All listed substitute parts are ROHS3 compliant except BK/S500-1.25-R, which is listed as RoHS Compliant (without the "3" designation). For applications requiring strict ROHS3 compliance, use 5MF 1.25-R, 0034.1517, 02171.25HXP, 02171.25MXP, 02171.25VXP, or 02351.25MXP.

Q: Which substitute part has the broadest international certification coverage?

A: The Littelfuse 217 series parts (02171.25HXP, 02171.25MXP, 02171.25VXP) carry the most comprehensive certification portfolio: BSI, CE, CCC, CSA, KC, PSE, SEMKO, UR, and VDE. These parts are suitable for applications requiring multi-region compliance.

Q: Can I use the 02351.25MXP (Littelfuse 235 series) as a direct replacement?

A: The 02351.25MXP meets all critical parameters (1.25 A, 250 V, 5x20mm cartridge glass, fast blow) and is mechanically compatible. However, it has a lower melting I²t (1.085 versus 2.5) and different breaking capacity (100 A versus 35 A), resulting in faster response to overcurrent. Verify that the application can tolerate this faster response characteristic before substitution.

Q: What does melting I²t represent, and why does it vary among these parts?

A: Melting I²t is a thermal characteristic that indicates the energy required to melt the fuse element. Lower values indicate faster response to overcurrent, while higher values indicate slower response. All parts listed maintain the same 1.25 A nominal rating but differ in response speed. Selection should match the application's overcurrent protection requirements.