3SB 300 Equivalent & Substitute Parts

Part Overview

The 3SB 300 is a 300 mA, 250 V AC/DC slow-blow glass cartridge fuse manufactured by Bel Fuse Inc. in the 3AB/3AG form factor (1/4" x 1-1/4"). This component is classified as obsolete, making identification of equivalent and substitute parts essential for system maintenance, repair, and redesign applications. Substitute parts must maintain electrical performance, mechanical compatibility, and regulatory compliance within the specified operating parameters.

Key Parameters

Parameter	Value
Current Rating	300 mA
Voltage Rating (AC)	250 V
Response Time	Slow Blow
Fuse Type	Cartridge, Glass
Package / Case	3AB, 3AG, 1/4" x 1-1/4"
Mounting Type	Requires Holder
Breaking Capacity @ Rated Voltage	35 A
Operating Temperature Range	-55°C ~ 125°C
Size / Dimension	0.250" Dia x 1.252" L (6.35mm x 31.80mm)

Substitute Part Grouping Explanation

Substitution eligibility for the 3SB 300 is determined by strict alignment of the following parameters:

Current Rating: 300 mA (exact match required)
Voltage Rating (AC): 250 V (exact match required)
Response Time: Slow Blow (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Package / Case: 3AB, 3AG, 1/4" x 1-1/4" (exact match required)
Mounting Type: Requires Holder (exact match required)
Operating Temperature Range: -55°C ~ 125°C (minimum requirement)

All identified substitute parts meet these core electrical and mechanical criteria. Substitute parts are categorized as direct manufacturer equivalents (0034.5215, 0313.300MXP, 0313.300VXP) and parametric equivalents (TSA-300MA) based on product status and availability.

Parameter Comparison

Parameter	3SB 300 (Bel Fuse)	0034.5215 (SCHURTER)	0313.300MXP (Littelfuse)	0313.300VXP (Littelfuse)	TSA-300MA (OptiFuse)
Current Rating (Amps)	300 mA	300 mA	300 mA	300 mA	300 mA
Voltage Rating - AC	250 V	250 V	250 V	250 V	250 V
Response Time	Slow Blow	Slow Blow	Slow Blow	Slow Blow	Slow Blow
Fuse Type	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass
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"
Mounting Type	Requires Holder	Requires Holder	Requires Holder	Requires Holder	Requires Holder
Breaking Capacity @ Rated Voltage	35 A	35 A	35 A	35 A	100 A
Operating Temperature	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C
Size / Dimension	0.250" Dia x 1.252" L (6.35mm x 31.80mm)	0.250" Dia x 1.250" L (6.35mm x 31.75mm)	0.250" Dia x 1.250" L (6.35mm x 31.75mm)	0.250" Dia x 1.250" L (6.35mm x 31.75mm)	0.250" Dia x 1.252" L (6.35mm x 31.80mm)
Product Status	Obsolete	Obsolete	Active	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Approval Agency	CE, CSA, PSE, UL	CSA, UL	CE, CSA, UL	CE, CSA, UL	cULus, UL 248

Engineering Selection Recommendations

For applications requiring the 3SB 300, the following selection criteria apply:

Active Product Status Priority: The Littelfuse 0313.300MXP and 0313.300VXP, and OptiFuse TSA-300MA are active products with current manufacturing support and availability. These are preferred for new designs and long-term supply chain stability.

Regulatory Compliance: All substitute parts maintain CE, CSA, and UL certifications. The Littelfuse parts (0313.300MXP, 0313.300VXP) and OptiFuse TSA-300MA are ROHS3 compliant, addressing modern environmental and regulatory requirements. The SCHURTER 0034.5215 is also ROHS3 compliant but carries obsolete product status.

Breaking Capacity Consideration: The OptiFuse TSA-300MA provides 100 A breaking capacity compared to 35 A in the original 3SB 300 and other substitutes. This higher breaking capacity offers enhanced protection margin in fault conditions without affecting normal operation.

Dimensional Compatibility: All substitute parts fit the 3AB/3AG holder form factor. Minor dimensional variations (0.002" length difference) do not affect mechanical compatibility or electrical performance.

Frequently Asked Questions (FAQ)

Q: Can the 0313.300MXP or 0313.300VXP be used as direct replacements for the 3SB 300?

A: Yes. Both Littelfuse parts meet all electrical and mechanical parameters: 300 mA current rating, 250 V AC voltage rating, slow-blow response, glass cartridge type, and 3AB/3AG form factor. Both are active products with current availability.

Q: What is the difference between the Littelfuse 0313.300MXP and 0313.300VXP?

A: Both parts are electrically and mechanically identical. They share the same current rating, voltage rating, response time, package, and operating temperature range. Selection between them is based on supplier availability and inventory.

Q: Why does the OptiFuse TSA-300MA have a higher breaking capacity (100 A vs. 35 A)?

A: Breaking capacity is determined by fuse design and internal construction. The TSA-300MA's higher breaking capacity provides enhanced fault protection without affecting normal circuit operation at 300 mA. This is a performance advantage for applications requiring higher fault current withstand capability.

Q: Is the SCHURTER 0034.5215 suitable for new designs?

A: The 0034.5215 meets all electrical and mechanical requirements and is ROHS3 compliant. However, it carries obsolete product status. For new designs, active products (Littelfuse 0313.300MXP, 0313.300VXP, or OptiFuse TSA-300MA) are recommended for long-term supply chain assurance.

Q: Are there any temperature or environmental differences between these parts?

A: All substitute parts operate within the same temperature range (-55°C ~ 125°C) as the original 3SB 300. Environmental compliance (REACH Unaffected, EAR99 classification) is consistent across all parts.

Q: Can these fuses be used interchangeably in the same holder?

A: Yes. All substitute parts are designed for the 3AB/3AG holder form factor with identical electrical and mechanical interfaces. Physical dimensions are within tolerance for standard holder compatibility.

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