SST 2.5 Equivalent & Substitute Parts

Part Overview

The SST 2.5 is a 2.5 A surface mount board mount fuse rated for 125 V AC/DC operation manufactured by Bel Fuse Inc. This component is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity. The SST 2.5 series provides slow blow response characteristics suitable for applications requiring transient surge protection in low-voltage circuits.

Key Parameters

Parameter	Value
Manufacturer Part Number	SST 2.5
Manufacturer	Bel Fuse Inc.
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	-55°C ~ 125°C
RoHS Status	ROHS3 Compliant
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution for the SST 2.5 is determined by the following critical parameters:

Current Rating: 2.5 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 parts are grouped into two categories:

Direct Manufacturer Substitutes (Bel Fuse 0680L Series): Parts 0680L2500-01, 0680L2500-11, 0680L2500-15, 0680L2500-21, and 0680L2500-25 are active production alternatives from the same manufacturer with identical electrical and mechanical specifications. These parts differ only in packaging configuration (Tape & Reel vs. Cut Tape) and internal construction details that do not affect functional performance.

Parametric Equivalents (Bel Fuse 0680H Series and Littelfuse NANO²® Series): Parts 0680H2500-01, 0680H2500-05, 0680L2500-05, 044902.5MR, and 045202.5MRL meet all critical electrical and mechanical parameters. These parts originate from different manufacturers or series but maintain identical current, voltage, response time, mounting, package, and dimensional specifications.

Parameter Comparison

Part Number	Manufacturer	Current Rating (A)	Voltage AC (V)	Voltage DC (V)	Response Time	Package / Case	Size (mm)	Breaking Capacity @ Rated Voltage	Melting I²t	DC Cold Resistance (Ω)	Product Status
SST 2.5	Bel Fuse Inc.	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	50A	9	0.044	Obsolete
0680L2500-01	Bel Fuse	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	50A AC, 100A DC	9	0.048	Active
0680L2500-11	Bel Fuse Inc.	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	50A AC, 100A DC	9	0.048	Active
0680L2500-15	Bel Fuse	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	50A AC, 100A DC	9	0.048	Active
0680L2500-21	Bel Fuse	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	50A AC, 100A DC	9	0.048	Active
0680L2500-25	Bel Fuse Inc.	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	50A AC, 100A DC	9	0.048	Active
0680H2500-01	Bel Fuse Inc.	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	100A AC, 500A DC	5.9	0.065	Active
0680H2500-05	Bel Fuse Inc.	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	100A AC, 500A DC	5.9	0.065	Active
0680L2500-05	Bel Fuse Inc.	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.54 x 2.54	50A AC, 100A DC	9	0.048	Active
044902.5MR	Littelfuse Inc.	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.69 x 2.69	50A	13.18	0.04	Active
045202.5MRL	Littelfuse Inc.	2.5	125	125	Slow Blow	2-SMD, Square End Block	6.10 x 2.69 x 2.69	50A	15	0.045	Active

Engineering Selection Recommendations

Primary Recommendation: The Bel Fuse 0680L series (0680L2500-01, 0680L2500-11, 0680L2500-15, 0680L2500-21, 0680L2500-25) represents the direct manufacturer replacement for the obsolete SST 2.5. All variants are in active production status and maintain identical electrical and mechanical specifications. Selection among these variants depends on packaging requirements: Tape & Reel (TR) for automated assembly or Cut Tape (CT) for manual placement. These parts carry AEC-Q200 and CE certifications matching the original part's compliance profile.

Secondary Recommendation: The Bel Fuse 0680H series (0680H2500-01, 0680H2500-05) and Bel Fuse 0680L2500-05 are parametric equivalents suitable for applications where higher breaking capacity is beneficial. The 0680H series provides 100A AC and 500A DC breaking capacity compared to the 50A AC and 100A DC of the 0680L series. These parts are in active production and carry cURus certification.

Alternative Recommendation: Littelfuse NANO²® series parts (044902.5MR and 045202.5MRL) are parametric equivalents meeting all critical electrical and mechanical parameters. These parts are in active production with cULus and PSE certifications. Dimensional variation exists in the width and height (2.69mm vs. 2.54mm), which may require PCB layout verification for space-constrained applications. The melting I²t values differ (13.18 and 15 respectively) compared to the original part (9), indicating different thermal response characteristics.

Frequently Asked Questions (FAQ)

Q: Can I use 0680L2500 variants interchangeably with SST 2.5?

A: Yes. All 0680L2500 variants (0680L2500-01, 0680L2500-11, 0680L2500-15, 0680L2500-21, 0680L2500-25) are direct functional replacements for SST 2.5. They maintain identical current rating (2.5 A), voltage rating (125 V AC/DC), response time (Slow Blow), mounting type (Surface Mount), package configuration (2-SMD, Square End Block), and dimensional specifications (6.10mm x 2.54mm x 2.54mm). Selection depends on packaging format required for your assembly process.

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

A: Both series meet the critical electrical and mechanical parameters of SST 2.5. The primary difference is breaking capacity: 0680L series provides 50A AC and 100A DC, while 0680H series provides 100A AC and 500A DC. The 0680H series also has a lower melting I²t value (5.9 vs. 9), indicating faster thermal response. Selection depends on the specific circuit protection requirements of your application.

Q: Can Littelfuse NANO²® parts replace SST 2.5?

A: Littelfuse 044902.5MR and 045202.5MRL meet all critical electrical parameters (2.5 A, 125 V AC/DC, Slow Blow, Surface Mount, 2-SMD Square End Block). However, dimensional variation exists: Littelfuse parts measure 6.10mm x 2.69mm x 2.69mm compared to 6.10mm x 2.54mm x 2.54mm for SST 2.5. Verify PCB footprint compatibility before substitution, particularly in space-constrained designs. Melting I²t values also differ (13.18 and 15 vs. 9), affecting thermal response characteristics.

Q: What certifications should I verify for my application?

A: SST 2.5 carries AEC-Q200, CE, CSA, and cULus certifications. Bel Fuse 0680L series maintains AEC-Q200, CE, and cURus certifications. Bel Fuse 0680H series carries cURus certification only. Littelfuse NANO²® parts carry cULus and PSE certifications. Confirm that substitute part certifications meet your application's regulatory requirements before implementation.

Q: Does packaging format affect electrical performance?

A: No. Packaging format (Tape & Reel vs. Cut Tape) affects only the delivery and handling method, not electrical or mechanical performance. All 0680L2500 variants deliver identical functional characteristics regardless of packaging configuration.

Q: Are there inventory considerations for substitute selection?

A: Yes. Current inventory levels vary: 0680L2500-05 has 6,748 pieces in stock, 0680H2500-05 has 6,053 pieces, and 045202.5MRL has 15,300 pieces available. For high-volume production, 045202.5MRL offers the largest available inventory. For applications requiring specific certifications or performance characteristics, inventory availability may influence substitute selection timing.

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