SST 500 Equivalent & Substitute Parts Reference

Part Overview

The SST 500 is a 500 mA, 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, though it remains in stock with 873 units available. Due to its obsolete status, direct replacements from active product lines are necessary for new designs and ongoing production requirements. Equivalent and substitute parts maintain identical electrical ratings and mechanical dimensions while offering improved availability through active product lines or alternative manufacturers.

Key Parameters

Parameter	Value
Current Rating	500 mA
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
Fuse Type	Board Mount (Cartridge Style Excluded)
Operating Temperature Range	-55°C ~ 125°C
Size / Dimension	0.240" L x 0.100" W x 0.100" H (6.10mm x 2.54mm x 2.54mm)
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution for the SST 500 is determined by strict equivalence across the following parameters: current rating (500 mA), voltage ratings (125 V AC and 125 V DC), response time (Slow Blow), package type (2-SMD, Square End Block), mounting method (Surface Mount), and physical dimensions (0.240" L x 0.100" W x 0.100" H). Parts are grouped into two categories:

Direct Substitutes (0680L Series): Parts 0680L0500-01, 0680L0500-05, 0680L0500-11, 0680L0500-15, 0680L0500-21, and 0680L0500-25 are manufactured by Bel Fuse Inc. with active product status. These maintain all electrical and mechanical parameters identical to the SST 500, with variations only in packaging format (Tape & Reel) and internal resistance specifications (0.58 Ohms vs. 0.49 Ohms for the main part).

Parametric Equivalents (0680H Series): Parts 0680H0500-01 and 0680H0500-05 are Bel Fuse Inc. products with identical current, voltage, and dimensional specifications. These differ in breaking capacity (100A AC, 500A DC vs. 50A) and melting I²t (0.13 vs. 0.27), representing a faster response characteristic.

Cross-Manufacturer Alternatives: Parts 0449.500MR and 0452.500MRL from Littelfuse Inc. maintain electrical ratings and dimensions within tolerance. The 0449.500MR (NANO²® 449 series) and 0452.500MRL (NANO²® 452 series) differ in dimensional tolerance (0.106" W x 0.106" H vs. 0.100" W x 0.100" H) and internal resistance values.

Parameter Comparison

Part Number	Manufacturer	Current Rating (mA)	Voltage AC (V)	Voltage DC (V)	Response Time	Breaking Capacity @ Rated Voltage	Melting I²t	DC Cold Resistance (Ohms)	Product Status	Inventory (Pcs)
SST 500	Bel Fuse Inc.	500	125	125	Slow Blow	50A	0.27	0.49	Obsolete	873
0680L0500-01	Bel Fuse Inc.	500	125	125	Slow Blow	50A AC, 100A DC	0.27	0.58	Active	2695
0680L0500-05	Bel Fuse Inc.	500	125	125	Slow Blow	50A AC, 100A DC	0.27	0.58	Active	33063
0680L0500-11	Bel Fuse	500	125	125	Slow Blow	50A AC, 100A DC	0.27	0.58	Active	1013
0680L0500-15	Bel Fuse Inc.	500	125	125	Slow Blow	50A AC, 100A DC	0.27	0.58	Active	921
0680L0500-21	Bel Fuse	500	125	125	Slow Blow	50A AC, 100A DC	0.27	0.58	Active	1040
0680L0500-25	Bel Fuse	500	125	125	Slow Blow	50A AC, 100A DC	0.27	0.58	Active	649
0680H0500-01	Bel Fuse Inc.	500	125	125	Slow Blow	100A AC, 500A DC	0.13	1.1	Active	922
0680H0500-05	Bel Fuse Inc.	500	125	125	Slow Blow	100A AC, 500A DC	0.13	1.1	Active	10908
0449.500MR	Littelfuse Inc.	500	125	125	Slow Blow	50A	0.258	0.7633	Active	3142
0452.500MRL	Littelfuse Inc.	500	125	125	Slow Blow	50A	0.24	0.7	Active	150200

Engineering Selection Recommendations

Primary Selection: The 0680L series (0680L0500-01, 0680L0500-05, 0680L0500-11, 0680L0500-15, 0680L0500-21, 0680L0500-25) represents the direct replacement path for the obsolete SST 500. All variants maintain identical electrical specifications and are manufactured by Bel Fuse Inc. with active product status. Selection among 0680L variants is determined by packaging preference (Tape & Reel format) and inventory availability. The 0680L0500-05 variant offers the highest inventory level (33,063 units), ensuring supply continuity.

Alternative Selection: The 0680H series (0680H0500-01, 0680H0500-05) provides parametric equivalence with enhanced breaking capacity specifications. These parts are suitable for applications requiring higher fault current handling. The 0680H0500-05 variant provides substantial inventory (10,908 units) and active product status.

Cross-Manufacturer Options: Littelfuse Inc. parts 0449.500MR and 0452.500MRL maintain electrical equivalence with dimensional tolerance variations. The 0452.500MRL offers exceptional inventory availability (150,200 units) and active product status, making it suitable for high-volume applications where dimensional tolerance of ±0.006" is acceptable.

Compliance Considerations: All substitute parts maintain ROHS3 compliance and MSL 1 rating. Approval agency certifications vary: the 0680L series carries AEC-Q200, CE, and cURus certifications; the 0680H series carries cURus certification only; Littelfuse parts carry cULus (0449.500MR) or CSA/UR (0452.500MRL) certifications.

Frequently Asked Questions (FAQ)

Q: Can the 0680L series directly replace the SST 500 without circuit modification?

A: Yes. The 0680L series maintains identical current rating (500 mA), 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). The primary difference is packaging format (Tape & Reel vs. Cut Tape) and internal resistance specification (0.58 Ohms vs. 0.49 Ohms), which does not affect circuit functionality.

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

A: Both series maintain identical current and voltage ratings. The 0680H series features higher breaking capacity (100A AC, 500A DC vs. 50A AC, 100A DC) and lower melting I²t (0.13 vs. 0.27), indicating faster response to fault conditions. The 0680H series also exhibits higher DC cold resistance (1.1 Ohms vs. 0.58 Ohms). Selection depends on application fault current requirements.

Q: Are Littelfuse parts 0449.500MR and 0452.500MRL mechanically compatible?

A: Both Littelfuse parts maintain the 0.240" length specification. However, width and height dimensions are 0.106" x 0.106" compared to the 0.100" x 0.100" specification of Bel Fuse parts. This represents a ±0.006" tolerance variation. Mechanical compatibility depends on PCB footprint design tolerance. Verify footprint specifications before selection.

Q: Which substitute part offers the best inventory availability?

A: The Littelfuse 0452.500MRL provides the highest inventory level at 150,200 units. Among Bel Fuse parts, the 0680L0500-05 offers 33,063 units. Both parts maintain active product status and electrical equivalence to the SST 500.

Q: Do all substitute parts carry the same regulatory certifications as the SST 500?

A: No. The SST 500 carries AEC-Q200, CE, CSA, and cULus certifications. The 0680L series carries AEC-Q200, CE, and cURus certifications (CSA certification is not listed). The 0680H series carries only cURus certification. Littelfuse parts carry cULus (0449.500MR) or CSA/UR (0452.500MRL) certifications. Verify certification requirements for your specific application before selection.

Q: What is the significance of the melting I²t parameter in fuse selection?

A: Melting I²t defines the thermal energy required to melt the fuse element. The SST 500 and 0680L series specify 0.27, while the 0680H series specifies 0.13. Lower I²t values indicate faster response to overcurrent conditions. Littelfuse parts specify 0.258 (0449.500MR) and 0.24 (0452.500MRL). Selection depends on circuit protection speed requirements.

Q: Can the SST 500 be used interchangeably with the 0680H series in existing designs?

A: Electrical substitution is possible due to identical current and voltage ratings. However, the 0680H series exhibits different response characteristics (lower melting I²t and higher breaking capacity). Circuit behavior may differ under fault conditions. Verify that enhanced fault current handling and faster response characteristics are compatible with circuit design intent before substitution.

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