SST 2 Equivalent & Substitute Parts

Part Overview

The SST 2 is a 2 A, 125 V AC/DC surface mount board mount fuse manufactured by Bel Fuse Inc. in a 2-SMD, Square End Block package. This part is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement continuity. The SST 2 meets AEC-Q200, CE, CSA, and cULus approvals with slow blow response characteristics suitable for circuit protection applications requiring 50 A breaking capacity at rated voltage.

Key Parameters

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

Substitute Part Grouping Explanation

Substitution for the SST 2 is based on strict electrical and mechanical parameter matching. All substitute parts must maintain identical current rating (2 A), voltage ratings (125 V AC/DC), response time (Slow Blow), package type (2-SMD, Square End Block), and physical dimensions (0.240" L x 0.100" W x 0.100" H). Operating temperature range (-55°C ~ 125°C) and RoHS3 compliance are also required for direct substitution.

Substitute parts are grouped into two categories:

Direct Manufacturer Substitutes (Bel Fuse 0680L Series): Parts 0680L2000-01, 0680L2000-05, 0680L2000-11, 0680L2000-15, 0680L2000-21, and 0680L2000-25 are active production equivalents from Bel Fuse Inc. These parts share identical electrical ratings, package configuration, and physical dimensions with the SST 2. All are ROHS3 compliant with unlimited moisture sensitivity rating.

Parametric Equivalents (Bel Fuse 0680H Series): Parts 0680H2000-01 and 0680H2000-05 meet all electrical and mechanical parameters but feature enhanced breaking capacity (100 A AC, 500 A DC) and lower melting I²t (3.6 versus 5 or 6). These are suitable where higher fault current withstand capability is required within the same package footprint.

Cross-Manufacturer Alternatives (Littelfuse NANO²® Series): Parts 0449002.MR and 0452002.MRL from Littelfuse Inc. provide functional equivalence with identical current, voltage, and package specifications. Dimensional variance is minimal (0.106" width and height versus 0.100"), and both maintain slow blow response and ROHS3 compliance.

Parameter Comparison

Part Number	Manufacturer	Current Rating (A)	Voltage AC (V)	Voltage DC (V)	Response Time	Package	Breaking Capacity @ Rated Voltage	Melting I²t	Product Status	DC Cold Resistance (Ω)
SST 2	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A	5	Obsolete	0.061
0680L2000-01	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A AC, 100 A DC	6	Active	0.068
0680L2000-05	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A AC, 100 A DC	6	Active	0.068
0680L2000-11	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A AC, 100 A DC	6	Active	0.068
0680L2000-15	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A AC, 100 A DC	6	Active	0.068
0680L2000-21	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A AC, 100 A DC	6	Active	0.068
0680L2000-25	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A AC, 100 A DC	6	Active	0.068
0680H2000-01	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	100 A AC, 500 A DC	3.6	Active	0.095
0680H2000-05	Bel Fuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	100 A AC, 500 A DC	3.6	Active	0.095
0449002.MR	Littelfuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A	6.76	Active	0.0708
0452002.MRL	Littelfuse Inc.	2	125	125	Slow Blow	2-SMD, Square End Block	50 A	8.2	Active	0.0625

Engineering Selection Recommendations

Primary Recommendation: The Bel Fuse 0680L series (0680L2000-01, 0680L2000-05, 0680L2000-11, 0680L2000-15, 0680L2000-21, 0680L2000-25) represents the most direct substitution path for the obsolete SST 2. All parts are in active production status, maintain identical electrical specifications and package dimensions, and carry AEC-Q200 and CE certifications. The 0680L series provides enhanced DC breaking capacity (100 A) compared to the SST 2 (50 A), offering improved fault tolerance without altering circuit protection characteristics.

Secondary Recommendation: The Bel Fuse 0680H series (0680H2000-01, 0680H2000-05) is suitable for applications requiring significantly higher breaking capacity (100 A AC, 500 A DC). These parts maintain identical current and voltage ratings but feature lower melting I²t (3.6 versus 5), resulting in faster response to fault conditions. Selection of the 0680H series should be based on specific fault current requirements and circuit protection coordination needs.

Alternative Recommendation: Littelfuse NANO²® 0449002.MR and 0452002.MRL provide functional equivalence with active production status. The 0449002.MR carries cULus and PSE approvals, while 0452002.MRL carries CSA, PSE, and UR approvals. Dimensional variance (0.106" versus 0.100" width and height) is within typical PCB layout tolerances for surface mount applications. Selection between these alternatives depends on specific certification requirements and supply chain considerations.

Frequently Asked Questions (FAQ)

Q: Can the 0680L series directly replace the SST 2 without PCB layout changes?

A: Yes. The 0680L series maintains identical physical dimensions (0.240" L x 0.100" W x 0.100" H) and 2-SMD, Square End Block package configuration as the SST 2. No PCB footprint modification is required.

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

A: Both series maintain identical current (2 A) and voltage ratings (125 V AC/DC). The primary differences are breaking capacity and melting I²t. The 0680L series provides 50 A AC and 100 A DC breaking capacity with melting I²t of 6. The 0680H series provides 100 A AC and 500 A DC breaking capacity with melting I²t of 3.6, resulting in faster fault response. Selection depends on circuit fault current levels and protection coordination requirements.

Q: Are the Littelfuse NANO²® parts compatible with existing SST 2 PCB layouts?

A: The Littelfuse parts feature slightly larger dimensions (0.106" width and height versus 0.100"). This dimensional difference is typically accommodated within standard PCB design tolerances for surface mount components. Verify specific PCB layout constraints before implementation.

Q: What certifications are maintained across all substitute parts?

A: All substitute parts maintain ROHS3 compliance and unlimited moisture sensitivity rating (MSL 1). Certification coverage varies: the Bel Fuse 0680L series carries AEC-Q200, CE, and cURus approvals. The 0680H series carries cURus approval. Littelfuse 0449002.MR carries cULus and PSE approvals. Littelfuse 0452002.MRL carries CSA, PSE, and UR approvals. Verify specific certification requirements for your application before selection.

Q: Can the 0680H series be used in applications originally designed for the SST 2?

A: The 0680H series is electrically compatible with the SST 2 for current and voltage ratings. However, the lower melting I²t (3.6 versus 5) results in faster response to overcurrent conditions. This may affect circuit protection coordination in systems with multiple fuses or protective devices. Conduct circuit analysis to confirm compatibility with existing protection schemes.

Q: What inventory levels are available for each substitute part?

A: Inventory availability varies. The 0680L2000-05 has the highest stock level at 21,535 pieces. Other 0680L variants range from 815 to 1,726 pieces. The 0680H2000-05 has 5,497 pieces in stock. Littelfuse 0452002.MRL has 141,490 pieces available. Littelfuse 0449002.MR has 1,900 pieces. Verify current inventory status with your supplier for procurement planning.

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