SST 4.6/5K Equivalent & Substitute Parts

Part Overview

The SST 4.6/5K is a 4.6 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, necessitating identification of active equivalent and substitute components for new designs and ongoing production requirements. Active alternatives from both Bel Fuse and Littelfuse product lines provide functional equivalence while maintaining electrical and mechanical compatibility within specified parameter tolerances.

Key Parameters

Parameter	Value
Current Rating	4.6 A
Voltage Rating (AC/DC)	125 V AC / 125 V DC
Response Time	Slow Blow
Mounting Type	Surface Mount
Package / Case	2-SMD, Square End Block
Physical Dimensions	0.240" L x 0.100" W x 0.100" H (6.10mm x 2.54mm x 2.54mm)
Operating Temperature Range	-55°C to 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 (4.6 A), voltage rating (125 V AC/DC), response time (slow blow), mounting type (surface mount), package configuration (2-SMD square end block), and physical dimensions (0.240" x 0.100" x 0.100"). Parts are grouped into two categories:

Direct Manufacturer Substitutes (Bel Fuse 0680L Series): Parts 0680L3500-01, 0680L3500-05, 0680L3500-11, 0680L3500-15, 0680L3500-21, and 0680L3500-25 are active production equivalents from the same manufacturer. All maintain identical electrical ratings, response characteristics, and physical form factors. These parts differ only in packaging configuration (all supplied as Tape & Reel) and represent the primary replacement path for the obsolete SST 4.6/5K.

Parametric Equivalents (Bel Fuse 0680H Series): Parts 0680H3500-01 and 0680H3500-05 meet all functional electrical and mechanical requirements but exhibit different breaking capacity ratings (100 A AC / 500 A DC versus 50 A AC / 100 A DC) and melting I²t characteristics (12 versus 18). These represent higher performance alternatives suitable for applications requiring enhanced fault current handling.

Cross-Manufacturer Alternatives (Littelfuse NANO²® Series): Parts 044904.6MR, 045204.6MRL, and 045204.6NRL from Littelfuse maintain electrical equivalence but feature slightly different physical dimensions (0.240" x 0.106" x 0.106") and melting I²t values. These are functionally compatible for applications where minor dimensional variation is acceptable.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating (A)	Voltage (AC/DC)	Response Time	Breaking Capacity (AC/DC)	Melting I²t	DC Cold Resistance (Ω)	Product Status	Inventory (Pcs)
SST 4.6/5K	Bel Fuse Inc.	SST	4.6	125/125	Slow Blow	50A	18	0.027	Obsolete	989
0680L3500-01	Bel Fuse Inc.	0680L	4.6	125/125	Slow Blow	50A AC / 100A DC	18	0.03	Active	2459
0680L3500-05	Bel Fuse Inc.	0680L	4.6	125/125	Slow Blow	50A AC / 100A DC	18	0.03	Active	10522
0680L3500-11	Bel Fuse Inc.	0680L	4.6	125/125	Slow Blow	50A AC / 100A DC	18	0.03	Active	929
0680L3500-15	Bel Fuse Inc.	0680L	4.6	125/125	Slow Blow	50A AC / 100A DC	18	0.03	Active	1027
0680L3500-21	Bel Fuse Inc.	0680L	4.6	125/125	Slow Blow	50A AC / 100A DC	18	0.03	Active	705
0680L3500-25	Bel Fuse Inc.	0680L	4.6	125/125	Slow Blow	50A AC / 100A DC	18	0.03	Active	936
0680H3500-01	Bel Fuse Inc.	0680H	4.6	125/125	Slow Blow	100A AC / 500A DC	12	0.042	Active	1138
0680H3500-05	Bel Fuse Inc.	0680H	4.6	125/125	Slow Blow	100A AC / 500A DC	12	0.042	Active	5435
044904.6MR	Littelfuse Inc.	NANO²® 449	4.6	125/125	Slow Blow	50A	32.7	0.0261	Active	1915
045204.6MRL	Littelfuse Inc.	NANO²® 452	4.6	125/125	Slow Blow	50A	26.53	0.0224	Active	18148

Engineering Selection Recommendations

Primary Recommendation: The Bel Fuse 0680L series (0680L3500-01, 0680L3500-05, 0680L3500-11, 0680L3500-15, 0680L3500-21, 0680L3500-25) represents the direct replacement path for the obsolete SST 4.6/5K. All variants maintain identical electrical specifications, response characteristics, and physical dimensions. Selection among these variants is determined by packaging and supply chain requirements. Part 0680L3500-05 offers the highest current inventory (10,522 pcs), ensuring supply continuity. All 0680L variants carry AEC-Q200 and CE certifications matching or exceeding the original part's compliance profile.

Secondary Recommendation: The Bel Fuse 0680H series (0680H3500-01, 0680H3500-05) provides parametric equivalence with enhanced breaking capacity specifications. These parts are suitable for applications requiring higher fault current withstand capability. The 0680H3500-05 variant provides substantial inventory availability (5,435 pcs). Note that AEC-Q200 certification is not listed for the 0680H series; verification against specific application requirements is necessary.

Cross-Manufacturer Alternative: Littelfuse NANO²® 045204.6MRL offers the highest inventory availability (18,148 pcs) among all alternatives and maintains full electrical equivalence. Physical dimensions differ slightly (0.106" width and height versus 0.100"), requiring PCB layout verification. This part carries CSA, PSE, and UR certifications. The melting I²t value (26.53) differs from the original specification (18), which may affect circuit protection coordination in sensitive applications.

Frequently Asked Questions (FAQ)

Q: Can I use 0680L3500 variants interchangeably with the SST 4.6/5K?

A: Yes. All 0680L3500 variants (01, 05, 11, 15, 21, 25) are direct electrical and mechanical equivalents. Differences exist only in packaging configuration and supplier tape specifications. Selection is based on supply availability and procurement requirements, not functional performance.

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

A: Both series maintain identical current rating (4.6 A), voltage rating (125 V AC/DC), and physical dimensions. The 0680H series features higher breaking capacity (100 A AC / 500 A DC versus 50 A AC / 100 A DC) and lower melting I²t (12 versus 18). The 0680H is suitable for applications requiring enhanced fault current handling but may provide faster response in normal operation due to lower I²t.

Q: Are Littelfuse NANO²® parts compatible with the original SST 4.6/5K footprint?

A: Electrical compatibility is confirmed. Physical dimensions differ slightly: Littelfuse parts measure 0.240" x 0.106" x 0.106" versus the original 0.240" x 0.100" x 0.100". PCB layout verification is required to confirm mechanical fit within existing component placement constraints.

Q: Which substitute part has the best supply availability?

A: Littelfuse 045204.6MRL offers the highest inventory (18,148 pcs). Among Bel Fuse alternatives, 0680L3500-05 provides the largest stock (10,522 pcs).

Q: Do all substitute parts carry the same certifications as the original SST 4.6/5K?

A: No. The original part lists AEC-Q200, CE, CSA, and cULus certifications. The 0680L series carries AEC-Q200, CE, and cURus. The 0680H series carries only cURus. Littelfuse NANO²® parts carry CSA, PSE, and UR certifications. Application-specific certification requirements must be verified before selection.

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

A: Melting I²t determines the thermal energy required to melt the fuse element and is critical for circuit protection coordination. The original SST 4.6/5K specifies 18. The 0680L series matches this value. The 0680H series specifies 12 (faster response), while Littelfuse parts range from 26.53 to 32.7 (slower response). Selection must align with circuit protection requirements and upstream device coordination.

Q: Can I mix different 0680L variants in the same production run?

A: Yes. All 0680L3500 variants are electrically and mechanically identical. Mixing is acceptable from a functional standpoint, though procurement and traceability practices may impose restrictions based on internal quality procedures.

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