SST 3/5K Surface Mount Fuse – Equivalent & Substitute Parts

Part Overview

The SST 3/5K is a 3 A, 125 V AC/DC surface mount board fuse manufactured by Bel Fuse Inc. in a 2-SMD, square end block package. This component is classified as obsolete, though 1,069 units remain in stock. Due to its obsolete status, identifying active equivalent and substitute parts is essential for ongoing design support, production continuity, and long-term component availability. Direct substitutes from the active 0680L series and parametric equivalents from the 0680H series provide functional alternatives with identical electrical ratings and mechanical dimensions.

Key Parameters

Parameter	Value
Current Rating	3 A
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Slow Blow
Package / Case	2-SMD, Square End Block
Size / Dimension	0.240" L x 0.100" W x 0.100" H (6.10mm x 2.54mm x 2.54mm)
Mounting Type	Surface Mount
Operating Temperature	-55°C ~ 125°C
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution for the SST 3/5K is determined by strict equivalence across the following parameters:

Critical Matching Parameters:

Current Rating: 3 A (exact match required)
Voltage Rating: 125 V AC and 125 V DC (exact match required)
Response Time: Slow Blow (exact match required)
Package / Case: 2-SMD, Square End Block (exact match required)
Size / Dimension: 0.240" L x 0.100" W x 0.100" H (exact match required)
Mounting Type: Surface Mount (exact match required)
Operating Temperature Range: -55°C ~ 125°C (exact match required)

Substitute Categories:

Direct Manufacturer Substitutes (0680L Series): Parts 0680L3000-01, 0680L3000-05, 0680L3000-11, 0680L3000-15, 0680L3000-21, and 0680L3000-25 are manufactured by Bel Fuse Inc. and meet all critical parameters. These parts are active products with higher inventory availability and differ only in packaging configuration (Tape & Reel) and minor variations in breaking capacity and melting I²t values.
Parametric Equivalents (0680H Series): Parts 0680H3000-01 and 0680H3000-05 are manufactured by Bel Fuse Inc. and match all critical electrical and mechanical parameters. These parts feature enhanced breaking capacity (100A AC, 500A DC versus 50A AC, 100A DC) and lower melting I²t values (8.3 versus 13–14), making them suitable for applications requiring higher fault current handling.
Cross-Manufacturer Alternatives (Littelfuse): Parts 0449003.MR and 0452003.MRL are manufactured by Littelfuse Inc. and meet all critical parameters. Minor dimensional variations exist (0.106" W x 0.106" H versus 0.100" W x 0.100" H), and melting I²t values differ (19.55–20.16 versus 13–14). These parts are active with substantial inventory availability.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating (A)	Voltage AC (V)	Voltage DC (V)	Response Time	Breaking Capacity AC (A)	Breaking Capacity DC (A)	Melting I²t	DC Cold Resistance (Ω)	Product Status	Packaging
SST 3/5K	Bel Fuse Inc.	SST	3	125	125	Slow Blow	50	50	14	0.033	Obsolete	-
0680L3000-01	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel (TR)
0680L3000-05	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel (TR)
0680L3000-11	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel (TR)
0680L3000-15	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel (TR)
0680L3000-21	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel (TR)
0680L3000-25	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel (TR)
0680H3000-01	Bel Fuse Inc.	0680H	3	125	125	Slow Blow	100	500	8.3	0.051	Active	Tape & Reel (TR)
0680H3000-05	Bel Fuse Inc.	0680H	3	125	125	Slow Blow	100	500	8.3	0.051	Active	Tape & Reel (TR)
0449003.MR	Littelfuse Inc.	NANO²® 449	3	125	125	Slow Blow	50	50	19.55	0.0352	Active	Tape & Reel (TR)
0452003.MRL	Littelfuse Inc.	NANO²® 452	3	125	125	Slow Blow	50	50	20.16	0.034	Active	Cut Tape (CT) & Digi-Reel®

Engineering Selection Recommendations

For Direct Replacement (Bel Fuse 0680L Series): The 0680L3000 variants (01, 05, 11, 15, 21, 25) are the primary substitutes for the obsolete SST 3/5K. All variants are active products with identical electrical ratings and mechanical dimensions. Selection among these variants depends on packaging and supply chain requirements. All carry AEC-Q200, CE, and cURus certifications, ensuring compliance with automotive and industrial standards. The 0680L series offers enhanced DC breaking capacity (100A DC versus 50A DC) compared to the SST 3/5K, providing improved fault current handling without affecting normal operation.

For Enhanced Fault Current Handling (Bel Fuse 0680H Series): The 0680H3000-01 and 0680H3000-05 are parametric equivalents suitable for applications requiring higher breaking capacity (100A AC, 500A DC). These parts maintain identical electrical ratings and mechanical dimensions but feature lower melting I²t values (8.3 versus 14), resulting in faster response to fault conditions. Certification is limited to cURus. Use this series only when enhanced fault current protection is a design requirement.

For Cross-Manufacturer Alternatives (Littelfuse NANO²® Series): The 0449003.MR and 0452003.MRL are active Littelfuse alternatives with identical electrical ratings. Minor dimensional variations exist (0.106" W x 0.106" H versus 0.100" W x 0.100" H), which may require PCB layout verification. Melting I²t values are higher (19.55–20.16 versus 14), indicating slower thermal response. These parts carry cULus and PSE certifications. Use this series when Littelfuse supply chain preference or specific packaging requirements (Cut Tape & Digi-Reel®) are necessary.

Frequently Asked Questions (FAQ)

Q: Can I use 0680L3000 variants interchangeably with the SST 3/5K? A: Yes. All 0680L3000 variants (01, 05, 11, 15, 21, 25) are direct substitutes with identical electrical ratings, response time, and mechanical dimensions. Selection depends on packaging format and inventory availability. All are active products manufactured by Bel Fuse Inc.

Q: What is the difference between the 0680L and 0680H series? A: Both series match the SST 3/5K in electrical ratings and mechanical dimensions. The 0680H series provides enhanced breaking capacity (100A AC, 500A DC versus 50A AC, 100A DC) and faster thermal response (melting I²t 8.3 versus 13). Use 0680H only if your application requires higher fault current protection.

Q: Are there dimensional differences between Bel Fuse and Littelfuse alternatives? A: Yes. Littelfuse NANO²® parts (0449003.MR and 0452003.MRL) have slightly larger dimensions (0.106" W x 0.106" H versus 0.100" W x 0.100" H). Verify PCB footprint compatibility before substitution. All parts maintain the same length (0.240") and height (0.100").

Q: Do all substitutes carry the same certifications as the SST 3/5K? A: No. The SST 3/5K carries AEC-Q200, CE, CSA, and cULus certifications. The 0680L series carries AEC-Q200, CE, and cURus. The 0680H series carries only cURus. Littelfuse alternatives carry cULus and PSE. Verify certification requirements for your application before selection.

Q: What does melting I²t indicate, and why does it vary among substitutes? A: Melting I²t is a thermal energy parameter that determines fuse response speed. Lower values indicate faster response to overcurrent. The SST 3/5K has melting I²t of 14. The 0680L series has 13 (slightly faster), the 0680H series has 8.3 (significantly faster), and Littelfuse alternatives have 19.55–20.16 (slower). Select based on your circuit protection requirements.

Q: Can I use Littelfuse alternatives if my design specifies Bel Fuse? A: Littelfuse alternatives are parametrically equivalent but carry different certifications and have minor dimensional and thermal response differences. Substitution requires design review and approval, particularly for dimensional compatibility and certification compliance.

Q: What packaging options are available for substitutes? A: Bel Fuse 0680L and 0680H series are supplied in Tape & Reel (TR) format. Littelfuse 0449003.MR is supplied in Tape & Reel (TR). Littelfuse 0452003.MRL is supplied in Cut Tape (CT) & Digi-Reel® format. Confirm packaging compatibility with your assembly process.

Q: Is the SST 3/5K still available for new designs? A: No. The SST 3/5K is classified as obsolete. For new designs, use active alternatives from the 0680L series (Bel Fuse) or NANO²® series (Littelfuse). Existing inventory of 1,069 units remains available for legacy production support.

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