Equivalent & Substitute Parts for 5SF 1.25 Glass Cartridge Fuse

Part Overview

The Bel Fuse Inc. 5SF 1.25 is a 1.25 A, 250 V AC/DC fast-blow glass cartridge fuse in 5mm x 20mm form factor. This part is classified as obsolete, necessitating identification of active equivalent and substitute components that maintain electrical and mechanical compatibility. Substitute parts must match the core electrical parameters: 1.25 A current rating, 250 V voltage rating, fast-blow response time, and 5mm x 20mm package dimensions.

Key Parameters

Parameter	5SF 1.25
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
Breaking Capacity @ Rated Voltage	35 A
Operating Temperature Range	-55°C ~ 125°C
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution is determined by strict equivalence in the following mandatory parameters:

Current Rating: 1.25 A (exact match required)
Voltage Rating: 250 V AC (exact match required)
Response Time: Fast Blow (exact match required)
Package / Case: 5mm x 20mm (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Mounting Type: Requires Holder (exact match required)
Operating Temperature Range: -55°C ~ 125°C (exact match required)

Secondary parameters including breaking capacity, melting I²t, DC cold resistance, and approval agencies may vary within acceptable engineering tolerances but do not disqualify substitution when primary parameters align.

Parts are grouped as follows:

Direct Manufacturer Equivalents (Bel Fuse Inc.): 5SF 1.25-R maintains identical electrical and mechanical specifications with active product status and improved RoHS compliance.

Parametric Equivalents (Alternative Manufacturers): 5MF 1.25-R (Bel Fuse Inc.), 0034.1517 (SCHURTER Inc.), and Littelfuse 217 series parts (02171.25HXP, 02171.25MXBP, 02171.25MXP, 02171.25TXP, 02171.25VXP) meet all mandatory electrical and mechanical parameters with active product status.

Similar Parts (Variant Series): 02351.25MXP (Littelfuse 235 series) meets all mandatory parameters but belongs to a different product series with different breaking capacity and melting I²t characteristics.

Parameter Comparison

Part Number	Manufacturer	Current Rating (A)	Voltage (V AC)	Response Time	Package	Breaking Capacity (A)	Melting I²t	Product Status	RoHS Status
5SF 1.25	Bel Fuse Inc.	1.25	250	Fast Blow	5mm x 20mm	35	2.5	Obsolete	Non-compliant
5SF 1.25-R	Bel Fuse Inc.	1.25	250	Fast Blow	5mm x 20mm	35	2.5	Active	ROHS3 Compliant
5MF 1.25-R	Bel Fuse Inc.	1.25	250	Fast Blow	5mm x 20mm	200	1.5	Active	ROHS3 Compliant
0034.1517	SCHURTER Inc.	1.25	250	Fast Blow	5mm x 20mm	35	1.81	Active	ROHS3 Compliant
02171.25HXP	Littelfuse Inc.	1.25	250	Fast Blow	5mm x 20mm	35	2.23	Active	ROHS3 Compliant
02171.25MXBP	Littelfuse Inc.	1.25	250	Fast Blow	5mm x 20mm	35	2.23	Active	ROHS3 Compliant
02171.25MXP	Littelfuse Inc.	1.25	250	Fast Blow	5mm x 20mm	35	2.23	Active	ROHS3 Compliant
02171.25TXP	Littelfuse Inc.	1.25	250	Fast Blow	5mm x 20mm	35	2.23	Active	ROHS3 Compliant
02171.25VXP	Littelfuse Inc.	1.25	250	Fast Blow	5mm x 20mm	35	2.23	Active	ROHS3 Compliant
02351.25MXP	Littelfuse Inc.	1.25	250	Fast Blow	5mm x 20mm	100	1.085	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: 5SF 1.25-R (Bel Fuse Inc.) is the direct active equivalent. It maintains identical electrical and mechanical specifications to the obsolete 5SF 1.25 while offering ROHS3 compliance and higher inventory availability (1,459 pcs vs. 983 pcs for the original part). Approval agencies include CCC, CE, CSA, cURus, IMQ, SEMKO, and VDE.

Alternative Selections: Littelfuse 217 series parts (02171.25HXP, 02171.25MXBP, 02171.25MXP, 02171.25TXP, 02171.25VXP) provide equivalent electrical and mechanical performance with broader approval agency coverage (BSI, CE, CCC, CSA, KC, PSE, SEMKO, UR, VDE). These parts are available in higher quantities (744–5,025 pcs) and carry ROHS3 compliance.

Secondary Alternatives: SCHURTER 0034.1517 (FSF 5x20 series) and Bel Fuse 5MF 1.25-R meet all mandatory parameters with active product status and ROHS3 compliance. The 5MF 1.25-R offers higher breaking capacity (200 A) and greater inventory (5,157 pcs).

Variant Consideration: Littelfuse 02351.25MXP (235 series) meets all mandatory electrical and mechanical parameters but features higher breaking capacity (100 A) and lower melting I²t (1.085). Selection depends on circuit protection requirements.

All recommended substitutes maintain the 5mm x 20mm form factor, 1.25 A current rating, 250 V voltage rating, fast-blow response time, and -55°C to 125°C operating temperature range required for direct replacement.

Frequently Asked Questions (FAQ)

Q: Can I use any of these substitute parts as a direct replacement for the 5SF 1.25?

A: Yes, all listed substitute parts meet the mandatory electrical and mechanical parameters: 1.25 A current rating, 250 V voltage rating, fast-blow response time, 5mm x 20mm package, and -55°C to 125°C operating temperature range. Physical form factor and holder compatibility are identical.

Q: What is the difference between the 5SF 1.25-R and the Littelfuse 217 series parts?

A: The 5SF 1.25-R is the direct active equivalent from the same manufacturer (Bel Fuse Inc.) with identical specifications. Littelfuse 217 series parts (02171.25HXP, 02171.25MXBP, 02171.25MXP, 02171.25TXP, 02171.25VXP) are from a different manufacturer but meet all mandatory parameters. Littelfuse parts offer broader approval agency coverage and higher inventory levels.

Q: Why do some substitute parts have different breaking capacities or melting I²t values?

A: Breaking capacity and melting I²t are secondary parameters that vary by manufacturer design while maintaining the same primary electrical characteristics (current rating, voltage rating, response time). These variations do not affect substitution eligibility when all mandatory parameters align. Selection should consider specific circuit protection requirements.

Q: Is the 02351.25MXP (235 series) a suitable substitute?

A: Yes, the 02351.25MXP meets all mandatory electrical and mechanical parameters. However, it belongs to a different product series (235 vs. 217) with different breaking capacity (100 A vs. 35 A) and melting I²t (1.085 vs. 2.23). Selection depends on whether the higher breaking capacity is compatible with circuit design requirements.

Q: What is the difference between the various Littelfuse 217 series part numbers?

A: All Littelfuse 217 series parts listed (02171.25HXP, 02171.25MXBP, 02171.25MXP, 02171.25TXP, 02171.25VXP) share identical electrical and mechanical specifications. Differences are in packaging designation and internal design variants. All are electrically equivalent for the 1.25 A, 250 V, fast-blow application.

Q: Are all substitute parts RoHS compliant?

A: All active substitute parts listed are ROHS3 compliant. The original 5SF 1.25 is RoHS non-compliant. Substitution with any listed part upgrades compliance status.

Q: Which substitute part has the highest inventory availability?

A: The Littelfuse 02171.25MXP has the highest inventory at 5,025 pcs. The Bel Fuse 5MF 1.25-R follows with 5,157 pcs. Both are suitable for high-volume applications.

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