3SB 125 Glass Cartridge Fuse Equivalent & Substitute Parts

Part Overview

The 3SB 125 is a 125 mA, 250 V AC/DC glass cartridge fuse manufactured by Bel Fuse Inc. in the 3SB series. This component is classified as obsolete, requiring identification of active equivalent parts for ongoing applications. The fuse is designed for use with 3AB and 3AG holders and provides slow-blow response characteristics suitable for circuit protection in industrial and commercial equipment.

Key Parameters

Parameter	Value
Current Rating	125 mA
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Response Time	Slow Blow
Package / Case	3AB, 3AG, 1/4" x 1-1/4"
Breaking Capacity @ Rated Voltage	35 A
Operating Temperature Range	-55°C ~ 125°C
Mounting Type	Requires Holder

Substitute Part Grouping Explanation

Substitution of the 3SB 125 is determined by strict equivalence across the following electrical and mechanical parameters:

Current Rating: 125 mA (exact match required)
Voltage Rating: 250 V AC (exact match required)
Response Time: Slow Blow (exact match required)
Package / Case: 3AB, 3AG, 1/4" x 1-1/4" (exact match required)
Breaking Capacity: 35 A (exact match required)
Operating Temperature Range: -55°C ~ 125°C (exact match required)

All identified substitute parts meet these criteria. The primary distinction between the main part and substitutes is product status: the 3SB 125 is obsolete, while substitute parts 0313.125MXP, 0313.125HXP, and 0313.125VXP are active. The part 0034.5208 (SCHURTER Inc.) is also obsolete but remains in inventory.

Parameter Comparison

Parameter	3SB 125 (Bel Fuse)	0034.5208 (SCHURTER)	0313.125HXP (Littelfuse)	0313.125MXP (Littelfuse)	0313.125VXP (Littelfuse)
Current Rating (Amps)	125 mA	125 mA	125 mA	125 mA	125 mA
Voltage Rating - AC	250 V	250 V	250 V	250 V	250 V
Fuse Type	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass
Response Time	Slow Blow	Slow Blow	Slow Blow	Slow Blow	Slow Blow
Package / Case	3AB, 3AG, 1/4" x 1-1/4"	3AB, 3AG, 1/4" x 1-1/4"	3AB, 3AG, 1/4" x 1-1/4"	3AB, 3AG, 1/4" x 1-1/4"	3AB, 3AG, 1/4" x 1-1/4"
Breaking Capacity @ Rated Voltage	35 A	35 A	35 A	35 A	35 A
Operating Temperature	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C
Approval Agency	CE, CSA, PSE, UL	CSA, UL	CE, CSA, UL	CE, CSA, UL	CE, CSA, UL
Product Status	Obsolete	Obsolete	Active	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

For new designs and ongoing applications, the Littelfuse 313 series parts (0313.125MXP, 0313.125HXP, 0313.125VXP) are the preferred substitutes. All three are active products with ROHS3 compliance and CE, CSA, and UL certifications. These parts provide equivalent electrical and mechanical performance to the 3SB 125 while offering current product support and compliance with modern regulatory requirements.

The SCHURTER 0034.5208 is electrically and mechanically equivalent but carries obsolete status. Selection of this part should be limited to legacy system maintenance where inventory availability is the primary consideration.

The 3SB 125 carries PSE approval in addition to CE, CSA, and UL certifications. When PSE certification is a specific requirement, compatibility with substitute parts should be confirmed against application-specific regulatory mandates.

Frequently Asked Questions (FAQ)

Q: Can the 0313.125MXP, 0313.125HXP, and 0313.125VXP be used interchangeably with the 3SB 125?

A: Yes. All three Littelfuse parts are direct electrical and mechanical equivalents. They share identical current ratings (125 mA), voltage ratings (250 V AC), response characteristics (slow blow), package dimensions (1/4" x 1-1/4"), and breaking capacity (35 A). They are compatible with the same 3AB and 3AG holders.

Q: What is the difference between 0313.125MXP, 0313.125HXP, and 0313.125VXP?

A: These three parts are functionally equivalent across all electrical and mechanical parameters provided in this reference. Differentiation between these variants is not specified in the available technical data and should be confirmed with the manufacturer for application-specific requirements.

Q: Why is the 3SB 125 marked as obsolete?

A: The 3SB 125 is no longer in active production by Bel Fuse Inc. Active equivalent parts from Littelfuse (0313.125MXP, 0313.125HXP, 0313.125VXP) are available for new applications and ongoing support.

Q: Are there RoHS compliance differences between the main part and substitutes?

A: Yes. The 3SB 125 is RoHS non-compliant, while all Littelfuse substitutes (0313.125MXP, 0313.125HXP, 0313.125VXP) are ROHS3 compliant. The SCHURTER 0034.5208 is also ROHS3 compliant. For applications requiring RoHS compliance, the Littelfuse parts are the appropriate selection.

Q: Can the 0034.5208 be used as a substitute?

A: The 0034.5208 is electrically and mechanically equivalent to the 3SB 125. However, it is marked as obsolete. It should be considered only for legacy system maintenance where existing inventory is available and product discontinuation is acceptable.

Q: What holder types are compatible with these fuses?

A: All listed parts require 3AB or 3AG holders. The physical dimensions (1/4" diameter x 1-1/4" length) are identical across all parts, ensuring mechanical compatibility with existing holder installations.

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