SST 1/5K Surface Mount Board Fuse – Equivalent & Substitute Parts

Part Overview

The SST 1/5K is a 1 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, with 781 pieces currently in stock. Due to its obsolete status, direct substitutes from active product lines are necessary for new designs and ongoing production requirements. Equivalent alternatives maintain the same electrical ratings, mechanical form factor, and thermal characteristics while offering improved availability and extended product lifecycle support.

Key Parameters

Parameter	Value
Manufacturer Part Number	SST 1/5K
Manufacturer	Bel Fuse Inc.
Current Rating	1 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
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
Product Status	Obsolete
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution for the SST 1/5K is determined by strict equivalence across the following electrical and mechanical parameters:

Primary Substitution Criteria:

Current Rating: 1 A (exact match required)
Voltage Rating: 125 V AC and 125 V DC (exact match required)
Response Time: Slow Blow (exact match required)
Mounting Type: Surface Mount (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)
Operating Temperature Range: -55°C ~ 125°C (exact match required)

Substitute Categories:

Direct Manufacturer Substitutes (Bel Fuse 0680L Series): Parts 0680L1000-01, 0680L1000-11, 0680L1000-15, 0680L1000-21, and 0680L1000-25 are active product line equivalents from Bel Fuse Inc. These parts maintain identical electrical ratings, response characteristics, and mechanical form factors. Differences in packaging format (Tape & Reel) and internal design parameters (Melting I²t: 1.5 vs. 1.2; DC Cold Resistance: 0.175 Ohms vs. 0.162 Ohms) do not affect functional substitution for board-level applications.

Parametric Equivalents (Bel Fuse 0680H Series): Parts 0680H1000-01 and 0680H1000-05 meet all primary substitution criteria with enhanced breaking capacity specifications (100A AC, 500A DC vs. 50A AC). These represent higher-performance alternatives suitable for applications requiring increased fault current handling.

Cross-Manufacturer Substitutes (Littelfuse NANO²® Series): Parts 0449001.MR and 0452001.MRL from Littelfuse Inc. maintain electrical equivalence across all critical parameters. Minor dimensional variations (0.106" W x 0.106" H vs. 0.100" W x 0.100" H) and different Melting I²t values (1.76 and 1.98 respectively) do not preclude functional substitution in standard board mount applications.

Parameter Comparison

Part Number	Manufacturer	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 1/5K	Bel Fuse Inc.	1	125	125	Slow Blow	50	—	1.2	0.162	Obsolete	—
0680L1000-01	Bel Fuse Inc.	1	125	125	Slow Blow	50	100	1.5	0.175	Active	Tape & Reel (TR)
0680L1000-11	Bel Fuse Inc.	1	125	125	Slow Blow	50	100	1.5	0.175	Active	Tape & Reel (TR)
0680L1000-15	Bel Fuse Inc.	1	125	125	Slow Blow	50	100	1.5	0.175	Active	Tape & Reel (TR)
0680L1000-21	Bel Fuse Inc.	1	125	125	Slow Blow	50	100	1.5	0.175	Active	Tape & Reel (TR)
0680L1000-25	Bel Fuse Inc.	1	125	125	Slow Blow	50	100	1.5	0.175	Active	Tape & Reel (TR)
0680H1000-01	Bel Fuse Inc.	1	125	125	Slow Blow	100	500	0.79	0.33	Active	Tape & Reel (TR)
0680H1000-05	Bel Fuse Inc.	1	125	125	Slow Blow	100	500	0.79	0.33	Active	Tape & Reel (TR)
0449001.MR	Littelfuse Inc.	1	125	125	Slow Blow	50	—	1.76	0.2516	Active	Tape & Reel (TR)
0452001.MRL	Littelfuse Inc.	1	125	125	Slow Blow	50	—	1.98	0.225	Active	Cut Tape (CT) & Digi-Reel®

Engineering Selection Recommendations

Primary Recommendation – Bel Fuse 0680L Series (0680L1000-01, 0680L1000-05): These parts are direct active-line replacements from the original manufacturer. Both maintain full electrical equivalence and are certified to AEC-Q200, CE, and cURus standards. The 0680L1000-05 variant offers the highest inventory availability (52,236 pieces) and is suitable for high-volume production. Selection between 0680L variants is determined by packaging and lead time requirements; all variants are functionally identical.

Secondary Recommendation – Bel Fuse 0680H Series (0680H1000-01, 0680H1000-05): These parts provide enhanced breaking capacity (100A AC, 500A DC) and are appropriate for applications subject to higher fault currents. The 0680H1000-05 variant has substantial inventory (5,730 pieces). Note that cURus certification is the only approval agency listed; applications requiring AEC-Q200 or CE certification should confirm compatibility with design specifications.

Cross-Manufacturer Alternative – Littelfuse 0452001.MRL: This NANO²® 452 series fuse meets all primary electrical and mechanical substitution criteria and carries CSA, PSE, and UR certifications. With 221,172 pieces in inventory, this part offers exceptional availability. The slightly larger package dimensions (0.106" W x 0.106" H) require PCB layout verification to confirm mechanical fit.

Not Recommended – Littelfuse 0449001.MR: While electrically equivalent, this NANO²® 449 series part has lower inventory (2,333 pieces) compared to other active alternatives and offers no certification or performance advantage over the 0680L or 0452001.MRL options.

Frequently Asked Questions (FAQ)

Q: Can I use a 0680H series fuse as a direct replacement for the SST 1/5K? A: Yes. The 0680H1000-01 and 0680H1000-05 meet all primary electrical and mechanical substitution criteria. The enhanced breaking capacity (100A AC, 500A DC vs. 50A AC) does not prevent functional substitution. However, verify that your application's certification requirements align with the available approval agencies (cURus only for 0680H series vs. AEC-Q200, CE, cURus for 0680L series).

Q: What is the difference between the various 0680L part numbers (0680L1000-01, -11, -15, -21, -25)? A: All 0680L variants are electrically and mechanically identical. The numeric suffixes (-01, -11, -15, -21, -25) denote different packaging configurations, tape formats, or manufacturing date codes. Selection is based on procurement and assembly equipment compatibility, not electrical performance.

Q: Can I substitute the Littelfuse 0452001.MRL for the SST 1/5K? A: Yes, with a mechanical verification step. The 0452001.MRL maintains electrical equivalence but has slightly larger package dimensions (0.106" W x 0.106" H vs. 0.100" W x 0.100" H). Confirm that your PCB layout accommodates the larger footprint before implementation.

Q: Why do some substitute parts have different Melting I²t values? A: Melting I²t is an internal thermal characteristic that affects the fuse's response curve under fault conditions. Variations (ranging from 0.79 to 1.98 across the substitute options) reflect different internal element designs. All listed substitutes maintain the same 1 A current rating and Slow Blow response classification, ensuring functional equivalence in standard board-level protection applications.

Q: Which substitute part has the best availability? A: The Littelfuse 0452001.MRL has the highest inventory at 221,172 pieces. Among Bel Fuse options, the 0680L1000-05 offers 52,236 pieces. Both are suitable for high-volume production without lead time constraints.

Q: Are all substitute parts RoHS3 compliant? A: Yes. All listed substitute parts carry ROHS3 Compliant status, matching the original SST 1/5K specification.

Q: What certifications should I prioritize when selecting a substitute? A: This depends on your application's regulatory requirements. The 0680L series (0680L1000-01, -11, -15, -21, -25) carries the broadest certification coverage: AEC-Q200, CE, and cURus. The 0680H series carries cURus only. The Littelfuse 0452001.MRL carries CSA, PSE, and UR. Verify that your target market and design standards align with the available certifications before final selection.

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