SST 2.5/5K Equivalent & Substitute Parts

Part Overview

The SST 2.5/5K is a 2.5 A surface mount board mount fuse manufactured by Bel Fuse Inc., rated for 125 V AC/DC operation with slow blow response characteristics. This part is classified as obsolete, making identification of active equivalent and substitute components essential for ongoing production support and design continuity. Active alternatives from both Bel Fuse and third-party manufacturers maintain the same electrical ratings and mechanical form factor, enabling direct functional replacement in existing circuit designs.

Key Parameters

Parameter	Value
Current Rating	2.5 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 Range	-55°C ~ 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 critical parameters: current rating (2.5 A), AC voltage rating (125 V), DC voltage rating (125 V), response time (slow blow), mounting type (surface mount), package configuration (2-SMD, square end block), and physical dimensions (0.240" L x 0.100" W x 0.100" H). All substitute parts listed maintain these core electrical and mechanical specifications.

Substitute parts are grouped into two categories:

Direct Manufacturer Substitutes (Bel Fuse 0680L Series): Parts 0680L2500-01, 0680L2500-05, 0680L2500-11, 0680L2500-15, 0680L2500-21, and 0680L2500-25 are active production equivalents from Bel Fuse Inc. These parts share identical electrical ratings, response characteristics, and physical form factors. Differences in part number suffixes (-01, -05, -11, -15, -21, -25) indicate packaging or tape configuration variations only, with no impact on electrical performance or mechanical compatibility.

Parametric Equivalents (Bel Fuse 0680H Series): Parts 0680H2500-01 and 0680H2500-05 maintain identical current, voltage, and response ratings but feature enhanced breaking capacity (100 A AC / 500 A DC versus 50 A AC / 100 A DC) and lower melting I²t (5.9 versus 9). These represent higher-performance alternatives suitable for applications requiring increased fault current handling.

Cross-Manufacturer Alternatives (Littelfuse NANO²® Series): Parts 044902.5MR and 045202.5MRL from Littelfuse Inc. provide functional equivalence with identical electrical ratings and physical dimensions. Minor variations in melting I²t (13.18 and 15 respectively) and DC cold resistance reflect design differences between manufacturers but do not preclude direct substitution in applications designed for the SST 2.5/5K specifications.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating (A)	Voltage AC (V)	Voltage DC (V)	Response Time	Breaking Capacity @ Rated Voltage	Melting I²t	Product Status	Packaging	Inventory (Pcs)
SST 2.5/5K	Bel Fuse Inc.	SST	2.5	125	125	Slow Blow	50A	9	Obsolete	-	715
0680L2500-01	Bel Fuse	0680L	2.5	125	125	Slow Blow	50A AC, 100A DC	9	Active	Tape & Reel (TR)	812
0680L2500-05	Bel Fuse Inc.	0680L	2.5	125	125	Slow Blow	50A AC, 100A DC	9	Active	Tape & Reel (TR)	6748
0680L2500-11	Bel Fuse Inc.	0680L	2.5	125	125	Slow Blow	50A AC, 100A DC	9	Active	Tape & Reel (TR)	945
0680L2500-15	Bel Fuse	0680L	2.5	125	125	Slow Blow	50A AC, 100A DC	9	Active	Tape & Reel (TR)	1108
0680L2500-21	Bel Fuse	0680L	2.5	125	125	Slow Blow	50A AC, 100A DC	9	Active	Tape & Reel (TR)	654
0680L2500-25	Bel Fuse Inc.	0680L	2.5	125	125	Slow Blow	50A AC, 100A DC	9	Active	Tape & Reel (TR)	1097
0680H2500-01	Bel Fuse Inc.	0680H	2.5	125	125	Slow Blow	100A AC, 500A DC	5.9	Active	Tape & Reel (TR)	899
0680H2500-05	Bel Fuse Inc.	0680H	2.5	125	125	Slow Blow	100A AC, 500A DC	5.9	Active	Tape & Reel (TR)	6053
044902.5MR	Littelfuse Inc.	NANO²® 449	2.5	125	125	Slow Blow	50A	13.18	Active	Tape & Reel (TR)	3800
045202.5MRL	Littelfuse Inc.	NANO²® 452	2.5	125	125	Slow Blow	50A	15	Active	Tape & Reel (TR)	15300

Engineering Selection Recommendations

For applications requiring direct replacement of the obsolete SST 2.5/5K, the Bel Fuse 0680L series (0680L2500-05, 0680L2500-15, 0680L2500-25) represents the primary recommendation. These parts maintain identical electrical specifications and are in active production with substantial inventory availability. The 0680L2500-05 variant offers the highest stock level (6748 units), ensuring supply continuity.

The Bel Fuse 0680H series (0680H2500-01, 0680H2500-05) provides enhanced fault current handling capability and is suitable for applications where increased breaking capacity is beneficial. These parts are fully compatible with existing PCB layouts and assembly processes.

Littelfuse NANO²® alternatives (044902.5MR, 045202.5MRL) are functionally equivalent and offer extended inventory (15300 units for 045202.5MRL). Selection between Bel Fuse and Littelfuse alternatives should be based on established supply chain relationships, qualification requirements, and design validation protocols specific to the end application.

All substitute parts maintain ROHS3 compliance, unlimited moisture sensitivity level (MSL 1), and operating temperature range (-55°C ~ 125°C) consistent with the original SST 2.5/5K specification.

Frequently Asked Questions (FAQ)

Q: Can the 0680L series parts be used as direct replacements for the SST 2.5/5K?

A: Yes. The 0680L2500 variants maintain identical current rating (2.5 A), voltage ratings (125 V AC/DC), response time (slow blow), mounting type (surface mount), and physical dimensions (0.240" L x 0.100" W x 0.100" H). These parts are electrically and mechanically interchangeable with the SST 2.5/5K.

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

A: Both series share identical current and voltage ratings. The 0680H series features higher breaking capacity (100 A AC / 500 A DC versus 50 A AC / 100 A DC) and lower melting I²t (5.9 versus 9). The 0680H is suitable for applications requiring enhanced fault current protection.

Q: Are the different 0680L part number suffixes (-01, -05, -11, -15, -21, -25) electrically different?

A: No. The suffixes indicate packaging or tape configuration variations only. All 0680L2500 variants are electrically identical and interchangeable from a circuit performance perspective.

Q: Can Littelfuse NANO²® parts replace the SST 2.5/5K?

A: Yes. The 044902.5MR and 045202.5MRL maintain the same current rating, voltage ratings, response time, and physical dimensions. Melting I²t values differ (13.18 and 15 respectively versus 9), reflecting design differences between manufacturers but not precluding functional substitution in applications designed for SST 2.5/5K specifications.

Q: What certifications apply to the substitute parts?

A: The Bel Fuse 0680L series holds AEC-Q200, CE, and cURus certifications. The 0680H series holds cURus certification. Littelfuse NANO²® parts hold cULus and PSE (044902.5MR) or CSA, PSE, and UR (045202.5MRL) certifications. Verify certification alignment with end-application requirements.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All listed substitute parts are ROHS3 compliant with MSL 1 (unlimited moisture sensitivity level), matching the original SST 2.5/5K specification.

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