Equivalent & Substitute Parts for 5SF 125

Part Overview

The 5SF 125 is a 125 mA, 250 V AC/DC fast-blow glass cartridge fuse in 5mm x 20mm form factor, manufactured by Bel Fuse Inc. This component is classified as obsolete, requiring identification of active equivalent alternatives for continued system support and procurement. Substitute parts must maintain identical electrical ratings, mechanical dimensions, and functional characteristics to ensure direct interchangeability in existing circuit protection applications.

Key Parameters

Parameter	Value
Current Rating	125 mA
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Response Time	Fast Blow
Package / Case	5mm x 20mm
Breaking Capacity @ Rated Voltage	35A
Operating Temperature Range	-55°C ~ 125°C
Mounting Type	Requires Holder

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following parameters:

Current Rating: 125 mA (exact match required)
Voltage Rating: 250 V AC (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Response Time: Fast Blow (exact match required)
Package Dimensions: 5mm x 20mm (exact match required)
Breaking Capacity: 35A (exact match required)
Operating Temperature: -55°C ~ 125°C (exact match required)

All substitute parts listed below meet these criteria and are classified as active products, providing long-term availability and supply chain continuity.

Parameter Comparison

Manufacturer Part Number	Manufacturer	Current Rating	Voltage Rating (AC)	Response Time	Package / Case	Breaking Capacity	Melting I²t	Operating Temperature	Product Status	RoHS Status
5SF 125	Bel Fuse Inc.	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.009	-55°C ~ 125°C	Obsolete	RoHS non-compliant
0034.1507	SCHURTER Inc.	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.00484	-55°C ~ 125°C	Active	ROHS3 Compliant
0217.125HXP	Littelfuse Inc.	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.00478	-55°C ~ 125°C	Active	ROHS3 Compliant
0217.125MXBP	Littelfuse Inc.	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.00478	-55°C ~ 125°C	Active	ROHS3 Compliant
0217.125MXP	Littelfuse Inc.	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.00478	-55°C ~ 125°C	Active	ROHS3 Compliant
0217.125TXP	Littelfuse Inc.	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.00478	-55°C ~ 125°C	Active	ROHS3 Compliant
0217.125VXP	Littelfuse Inc.	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.00478	-55°C ~ 125°C	Active	ROHS3 Compliant
0235.125HXP	Littelfuse Inc.	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.00273	-55°C ~ 125°C	Active	ROHS3 Compliant
S500-125-R	Eaton - Electronics Division	125 mA	250 V	Fast Blow	5mm x 20mm	35A	0.005	-55°C ~ 125°C	Active	ROHS3 Compliant

Engineering Selection Recommendations

All listed substitute parts are active products with current manufacturing status, ensuring long-term availability and supply chain reliability. The Littelfuse 217 series (0217.125HXP, 0217.125MXBP, 0217.125MXP, 0217.125TXP, 0217.125VXP) and SCHURTER FSF 5x20 series (0034.1507) provide the broadest regulatory compliance coverage, including CCC, CE, CSA, UL, and VDE certifications. The Littelfuse 235 series (0235.125HXP) and Eaton S500 series (S500-125-R) are also fully compliant alternatives.

All substitute parts are RoHS3 compliant, addressing environmental and regulatory requirements that the obsolete 5SF 125 does not meet. Selection should prioritize parts with active product status and established supply chain presence for procurement continuity.

Frequently Asked Questions (FAQ)

Q: Can the 5SF 125 be directly replaced with any of the listed substitutes?

A: Yes. All listed substitute parts maintain identical electrical ratings (125 mA, 250 V AC), response characteristics (fast-blow), mechanical dimensions (5mm x 20mm), and breaking capacity (35A). Direct interchangeability is confirmed for all listed alternatives.

Q: What is the difference between the Littelfuse 217 series variants (0217.125HXP, 0217.125MXBP, 0217.125MXP, 0217.125TXP, 0217.125VXP)?

A: All Littelfuse 217 series variants share identical electrical and mechanical specifications. Differences are limited to packaging configurations and internal construction variants. Selection among these variants depends on specific procurement and packaging requirements.

Q: Are there compliance differences between substitute options?

A: The Littelfuse 217 series and SCHURTER 0034.1507 provide the most comprehensive regulatory certifications (CCC, CE, CSA, UL, VDE). The Littelfuse 235 series and Eaton S500 series provide reduced but still substantial certification coverage. All substitutes are RoHS3 compliant, unlike the obsolete 5SF 125.

Q: What is the significance of Melting I²t values in the parameter comparison?

A: Melting I²t represents the thermal energy required to melt the fuse element. While substitute parts show variation in this parameter (0.00273 to 0.009), all maintain the same current rating and response time classification. These variations reflect different internal construction methods but do not affect functional interchangeability for the specified 125 mA, 250 V fast-blow application.

Q: Does the 5mm x 20mm package dimension apply to all substitutes?

A: Yes. All substitute parts are specified with 5mm x 20mm dimensions and are compatible with standard 5x20mm fuse holders. Physical interchangeability is confirmed across all alternatives.

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