SSQ 1.25/5K Equivalent & Substitute Parts

Part Overview

The SSQ 1.25/5K is a 1.25 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 fuse features fast blow response characteristics and is housed in a 2-SMD square end block package suitable for automated assembly processes.

Key Parameters

Parameter	Value
Current Rating	1.25 A
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Fast Blow
Mounting Type	Surface Mount
Package / Case	2-SMD, Square End Block
Operating Temperature Range	-55°C to 125°C
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution for the SSQ 1.25/5K is determined by strict equivalence across the following critical parameters:

Direct Equivalents maintain identical electrical and mechanical specifications:

Current rating: 1.25 A
Voltage rating: 125 V AC and 125 V DC
Response time: Fast Blow
Package: 2-SMD, Square End Block
Operating temperature: -55°C to 125°C
RoHS3 compliance

Direct Substitutes meet all electrical requirements but may have minor dimensional or resistance variations within acceptable tolerances:

Current rating: 1.25 A
Voltage rating: 125 V AC and 125 V DC
Response time: Fast Blow
Package: 2-SMD, Square End Block

Similar Parts share the same current rating and package but differ in voltage rating or other electrical characteristics, requiring application-level verification before substitution.

Parameter Comparison

Part Number	Manufacturer	Current Rating (A)	Voltage AC (V)	Voltage DC (V)	Response Time	Breaking Capacity AC	Breaking Capacity DC	Melting I²t	DC Cold Resistance (Ω)	Size L x W x H (mm)	Product Status
SSQ 1.25/5K	Bel Fuse Inc.	1.25	125	125	Fast Blow	50A	300A	0.33	0.065	6.10 x 2.54 x 2.54	Obsolete
0679L1250-05	Bel Fuse Inc.	1.25	125	125	Fast Blow	50A	300A	0.22	0.072	6.10 x 2.54 x 2.79	Active
04761.25MR	Littelfuse Inc.	1.25	250	125	Fast Blow	100A	300A	0.276	0.122	6.10 x 2.69 x 2.69	Active
04761.25MRSN	Littelfuse	1.25	250	125	Fast Blow	100A	300A	0.276	0.122	6.10 x 2.69 x 2.69	Active
04511.25MRSN	Littelfuse Inc.	1.25	125	—	Fast Blow	50A	—	0.664	0.078	6.10 x 2.69 x 2.69	Active

Engineering Selection Recommendations

For Direct Replacement (Preferred): The 0679L1250-05 from Bel Fuse Inc. is the primary direct substitute. Both parts maintain identical voltage ratings (125 V AC/DC), current rating (1.25 A), and fast blow response. The 0679L1250-05 is active production status with AEC-Q200 and cURus certifications. Minor dimensional variation in height (2.79 mm vs. 2.54 mm) and melting I²t difference (0.22 vs. 0.33) are within acceptable substitution parameters for board mount fuse applications.

For Enhanced Voltage Capability: The 04761.25MR and 04761.25MRSN from Littelfuse Inc. (NANO²® 476 series) provide 250 V AC rating while maintaining 125 V DC compatibility. These parts are active production with cURus certification and offer increased breaking capacity (100A AC vs. 50A AC). Selection of these parts is appropriate for applications requiring higher AC voltage margin or where 250 V AC operation is specified.

For AC-Only Applications: The 04511.25MRSN from Littelfuse Inc. (NANO²® 451 series) is suitable for 125 V AC applications where DC voltage rating is not a requirement. This part is active production with CSA and UR certifications. The higher melting I²t value (0.664) indicates different thermal response characteristics compared to the original part.

Frequently Asked Questions (FAQ)

Q: Can the 0679L1250-05 be used as a direct replacement for SSQ 1.25/5K? A: Yes. Both parts share identical electrical specifications (1.25 A, 125 V AC/DC, fast blow response) and package type (2-SMD square end block). The 0679L1250-05 is active production status, making it the recommended direct substitute.

Q: What is the difference between the Littelfuse 04761.25MR and 04761.25MRSN? A: Both parts are electrically identical with 1.25 A current rating, 250 V AC / 125 V DC voltage rating, and fast blow response. The primary difference is packaging: 04761.25MR and 04761.25MRSN are both supplied in Tape & Reel format. Verify packaging requirements for your procurement process.

Q: Can I use a 250 V AC rated fuse in a 125 V AC circuit? A: Yes. A fuse rated for higher voltage can be used in lower voltage applications. The 04761.25MR and 04761.25MRSN (250 V AC rated) are suitable for 125 V AC circuits and provide additional voltage margin. Verify that current rating (1.25 A) and response time (fast blow) match application requirements.

Q: What does the melting I²t value indicate? A: Melting I²t is a thermal energy parameter that characterizes fuse response time. Lower values indicate faster response. The SSQ 1.25/5K has melting I²t of 0.33, while the 0679L1250-05 has 0.22. Both are fast blow fuses; the difference reflects manufacturing variations between series.

Q: Are all substitute parts RoHS3 compliant? A: Yes. All listed substitute parts are RoHS3 compliant and REACH unaffected or REACH compliant, meeting current environmental regulations.

Q: What certifications should I verify for my application? A: The 0679L1250-05 carries AEC-Q200 and cURus certifications. The Littelfuse parts (04761 and 04511 series) carry cURus, CSA, or UR certifications. Verify that the selected part's certifications align with your application and regional requirements.

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