SST 3 Board Mount Surface Mount Fuse – Equivalent & Substitute Parts

Part Overview

The SST 3 is a 3 A, 125 V AC/DC board mount surface mount fuse manufactured by Bel Fuse Inc. in a 2-SMD, Square End Block package. This component is classified as obsolete product status. Direct substitutes and parametric equivalents are available from active product lines within Bel Fuse and alternative manufacturers, enabling continued design support and procurement flexibility for applications requiring 3 A slow blow fuse protection at 125 V AC/DC ratings.

Key Parameters

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

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following parameters: current rating (3 A), AC voltage rating (125 V), DC voltage rating (125 V), response time (Slow Blow), mounting type (Surface Mount), package type (2-SMD, Square End Block), and physical dimensions (0.240" L × 0.100" W × 0.100" H). Parts meeting all these criteria are classified as direct substitutes or parametric equivalents.

Direct Manufacturer Substitutes (Bel Fuse 0680L Series): Parts 0680L3000-01, 0680L3000-11, 0680L3000-15, 0680L3000-21, and 0680L3000-25 are active product variants within the same manufacturer's 0680L series. These maintain identical electrical ratings and physical form factors while differing in packaging configuration (Tape & Reel) and internal design specifications such as breaking capacity and melting I²t values.

Parametric Equivalents (Bel Fuse 0680H Series): Parts 0680H3000-01 and 0680H3000-05 meet all core electrical and mechanical parameters but feature enhanced breaking capacity (100 A AC, 500 A DC versus 50 A AC, 100 A DC) and lower melting I²t (8.3 versus 13). These represent higher performance variants suitable for applications requiring increased fault current handling.

Cross-Manufacturer Alternatives (Littelfuse NANO²® Series): Parts 0449003.MR and 0452003.MRL from Littelfuse Inc. maintain identical electrical ratings and physical dimensions but exhibit minor dimensional variations (0.106" W × 0.106" H versus 0.100" W × 0.100" H) and different melting I²t characteristics (19.55 and 20.16 respectively). These are functionally equivalent for 3 A, 125 V AC/DC applications.

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	Bel Fuse Inc.	SST	3	125	125	Slow Blow	50	—	14	0.033	Obsolete	—
0680L3000-01	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel
0680L3000-11	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel
0680L3000-15	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel
0680L3000-21	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel
0680L3000-25	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel
0680H3000-01	Bel Fuse Inc.	0680H	3	125	125	Slow Blow	100	500	8.3	0.051	Active	Tape & Reel
0680H3000-05	Bel Fuse Inc.	0680H	3	125	125	Slow Blow	100	500	8.3	0.051	Active	Tape & Reel
0680L3000-05	Bel Fuse Inc.	0680L	3	125	125	Slow Blow	50	100	13	0.037	Active	Tape & Reel
0449003.MR	Littelfuse Inc.	NANO²® 449	3	125	125	Slow Blow	50	—	19.55	0.0352	Active	Tape & Reel
0452003.MRL	Littelfuse Inc.	NANO²® 452	3	125	125	Slow Blow	50	—	20.16	0.034	Active	Cut Tape & Digi-Reel®

Engineering Selection Recommendations

Primary Substitutes – Bel Fuse 0680L Series (0680L3000-01, 0680L3000-11, 0680L3000-15, 0680L3000-21, 0680L3000-25, 0680L3000-05): These active product variants from the same manufacturer provide direct electrical and mechanical compatibility with the obsolete SST 3. All variants carry AEC-Q200 and CE certifications (except 0680L3000-15 and 0680L3000-21, which carry CE and cURus). These are the preferred substitutes for applications requiring continuity with the original design.

Secondary Substitutes – Bel Fuse 0680H Series (0680H3000-01, 0680H3000-05): These parametric equivalents maintain identical electrical ratings and physical form factors but provide enhanced breaking capacity (100 A AC, 500 A DC) and lower melting I²t (8.3). Selection of 0680H variants is appropriate for applications subject to higher fault current environments or where improved performance margins are required. Certification is limited to cURus.

Cross-Manufacturer Alternatives – Littelfuse NANO²® Series (0449003.MR, 0452003.MRL): These parts meet all core electrical and mechanical substitution criteria and carry active product status. The 0449003.MR carries cULus and PSE certifications; the 0452003.MRL carries CSA, PSE, and UR certifications. Minor dimensional variations (0.106" versus 0.100" in width and height) and higher melting I²t values (19.55 and 20.16 versus 14) are present. These alternatives are suitable where cross-manufacturer sourcing is acceptable and certification requirements align.

Frequently Asked Questions (FAQ)

Q: Can 0680L3000 series parts directly replace the obsolete SST 3?

A: Yes. The 0680L3000 series maintains identical electrical ratings (3 A, 125 V AC/DC, Slow Blow), mounting type (Surface Mount), and physical dimensions (0.240" L × 0.100" W × 0.100" H). All variants are active products with established supply chains. Packaging differs (Tape & Reel versus original configuration), but electrical and mechanical form factors are equivalent.

Q: What is the difference between 0680L and 0680H series fuses?

A: Both series meet the 3 A, 125 V AC/DC electrical specification. The 0680H series provides higher breaking capacity (100 A AC, 500 A DC versus 50 A AC, 100 A DC) and lower melting I²t (8.3 versus 13). The 0680H is suitable for applications with higher fault current exposure or where faster response is required. Certification scope differs: 0680L carries AEC-Q200 and CE; 0680H carries only cURus.

Q: Are Littelfuse NANO²® parts (0449003.MR, 0452003.MRL) compatible with the SST 3?

A: Functionally, yes. Both Littelfuse parts maintain the 3 A, 125 V AC/DC rating, Slow Blow response, and 2-SMD Square End Block package. Minor dimensional variations exist (0.106" W × 0.106" H versus 0.100" W × 0.100" H). Melting I²t values are higher (19.55 and 20.16 versus 14). Certification differs: 0449003.MR carries cULus and PSE; 0452003.MRL carries CSA, PSE, and UR. Cross-manufacturer substitution is acceptable where certifications align with application requirements.

Q: What packaging options are available for substitute parts?

A: Bel Fuse 0680L and 0680H series are supplied in Tape & Reel (TR) packaging. Littelfuse 0449003.MR is supplied in Tape & Reel; 0452003.MRL is supplied in Cut Tape (CT) & Digi-Reel®. Original SST 3 packaging is not specified in available data. Confirm packaging compatibility with assembly equipment and procurement specifications.

Q: Which substitute offers the best compliance coverage?

A: Bel Fuse 0680L3000-05 carries the broadest certification scope: AEC-Q200, CE, and cURus. This variant is recommended for applications requiring automotive-grade qualification or multi-regional compliance. For non-automotive applications, any 0680L variant meets standard industrial certifications.

Q: How do melting I²t values affect fuse selection?

A: Melting I²t determines the thermal energy required to melt the fuse element. The SST 3 has a melting I²t of 14. Bel Fuse 0680L variants have 13 (slightly faster response); 0680H variants have 8.3 (significantly faster response). Littelfuse parts have 19.55–20.16 (slower response). Selection depends on circuit protection requirements: faster response (lower I²t) for sensitive circuits; slower response (higher I²t) for circuits with inrush current tolerance.

Q: Is the DC cold resistance difference significant between substitutes?

A: DC cold resistance values range from 0.033 Ω (SST 3) to 0.051 Ω (0680H series). These differences are minor and do not affect circuit operation in typical applications. For precision current-limiting applications, confirm resistance specifications with circuit design requirements.

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