SSQ 250 Equivalent & Substitute Parts

Part Overview

The SSQ 250 is a 250 mA surface mount board mount fuse rated for 125 V AC/DC operation with fast blow response characteristics. Manufactured by Bel Fuse Inc., this component is classified as obsolete, necessitating identification of active equivalent alternatives for new designs and ongoing production requirements. The SSQ series has been superseded by functionally equivalent active product lines from multiple manufacturers that maintain electrical and mechanical compatibility within specified tolerance ranges.

Key Parameters

Parameter	Value
Current Rating	250 mA
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Fast Blow
Mounting Type	Surface Mount
Fuse Type	Board Mount (Cartridge Style Excluded)
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 eligibility for the SSQ 250 is determined by strict equivalence across the following critical parameters:

Current Rating: 250 mA (exact match required)
Voltage Rating: 125 V AC and 125 V DC (exact match required)
Response Time: Fast Blow (exact match required)
Mounting Type: Surface Mount (exact match required)
Package Configuration: 2-SMD format (exact match required)
Operating Temperature Range: -55°C to 125°C minimum (exact match or wider range acceptable)
RoHS Compliance: ROHS3 Compliant (exact match required)

Substitute parts are classified into two categories:

Direct Substitutes: Parts meeting all critical electrical and mechanical parameters with identical or superior specifications.

Similar Substitutes: Parts meeting all critical electrical parameters with minor mechanical variations (dimensional tolerance, package lead style, or melting I²t characteristics) that do not affect functional performance in the specified application envelope.

Parameter Comparison

Parameter	SSQ 250	0679L0250-01	0451.250MRL	0451.250MRSN	0453.250MR	3404.0006.22
Manufacturer	Bel Fuse Inc.	Bel Fuse Inc.	Littelfuse Inc.	Littelfuse Inc.	Littelfuse Inc.	SCHURTER Inc.
Current Rating (mA)	250	250	250	250	250	250
Voltage Rating AC (V)	125	125	125	125	125	125
Voltage Rating DC (V)	125	125	125	—	125	125
Response Time	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Package / Case	2-SMD, Square End Block	2-SMD, Square End Block	2-SMD, Square End Block	2-SMD, Square End Block	2-SMD, Square End Block	2-SMD, J-Lead
Size (mm)	6.10 x 2.54 x 2.54	6.10 x 2.54 x 2.79	6.10 x 2.69 x 2.69	6.10 x 2.69 x 2.69	6.10 x 2.69 x 2.69	7.40 x 3.10 x 2.60
DC Cold Resistance (Ohms)	0.56	0.61	0.5765	0.5765	0.5765	—
Melting I²t	0.02	0.02	0.0158	0.0158	0.0158	0.0058
Breaking Capacity @ Rated Voltage	50A AC, 300A DC	50A AC, 300A DC	50A	50A	50A	100A
Operating Temperature Range	-55°C to 125°C	-55°C to 125°C	-55°C to 125°C	-55°C to 125°C	-55°C to 125°C	-55°C to 125°C
Product Status	Obsolete	Active	Active	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Approval Agency	CE, CSA, cULus	AEC-Q200, cURus	CSA, UL	CSA, UR	CSA, UL	cURus

Engineering Selection Recommendations

0679L0250-01 (Bel Fuse Inc.): Direct manufacturer successor within the Bel Fuse product portfolio. Maintains identical electrical specifications and breaking capacity. Packaging format is identical. Height dimension increases from 2.54 mm to 2.79 mm; verify PCB layout clearance. Active product status with AEC-Q200 qualification supports automotive and high-reliability applications. Recommended for designs requiring continuity with original Bel Fuse sourcing.

0451.250MRL (Littelfuse Inc., NANO²® 451 Series): Active product with full electrical equivalence. Dimensional variations in width and height (2.69 mm vs. 2.54 mm) require PCB layout verification. Melting I²t specification is lower (0.0158 vs. 0.02), indicating faster thermal response. DC cold resistance is within acceptable tolerance. UL and CSA certifications support broad industrial and consumer applications. Highest inventory availability (20,400 units) supports supply chain continuity.

0451.250MRSN (Littelfuse Inc., NANO²® 451 Series): Similar substitute with identical electrical performance to 0451.250MRL. DC voltage rating specification is not explicitly stated; verify DC application compatibility before selection. Identical dimensional and thermal characteristics. Lower inventory (813 units) may impact procurement timelines.

0453.250MR (Littelfuse Inc., NANO²® 453 Series): Similar substitute meeting all critical electrical parameters. Dimensional profile identical to 0451.250MRL and 0451.250MRSN variants. Melting I²t and DC cold resistance specifications match 0451.250MRL. UL and CSA certifications. Moderate inventory availability (10,100 units). Suitable for applications where NANO²® 453 series qualification is acceptable.

3404.0006.22 (SCHURTER Inc., OMF 125 Series): Similar substitute with package lead style variation (J-Lead vs. Square End Block). Dimensional differences are significant (7.40 x 3.10 x 2.60 mm); PCB layout redesign may be required. Melting I²t is substantially lower (0.0058), indicating significantly faster thermal response. Breaking capacity is superior (100A). cURus certification. Selection requires confirmation that J-Lead package and accelerated thermal response are compatible with application requirements.

Frequently Asked Questions (FAQ)

Q: Can the SSQ 250 be directly replaced with any of these substitute parts without PCB modification?

A: The 0679L0250-01 maintains identical package footprint and can be used as a direct replacement if PCB clearance accommodates the increased height (2.79 mm vs. 2.54 mm). The Littelfuse NANO²® 451 and 453 series parts (0451.250MRL, 0451.250MRSN, 0453.250MR) have identical length (6.10 mm) but increased width and height (2.69 mm), requiring verification of PCB layout clearance. The SCHURTER 3404.0006.22 has significantly different dimensions and J-Lead package configuration, requiring PCB redesign.

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

A: Melting I²t defines the thermal energy required to melt the fuse element. The SSQ 250 has a melting I²t of 0.02. Substitute parts with lower melting I²t values (0.0158 for Littelfuse parts, 0.0058 for SCHURTER) will respond faster to overcurrent conditions. This characteristic must be evaluated against circuit protection requirements to ensure the substitute does not create nuisance trips or inadequate protection.

Q: Are all substitute parts suitable for both AC and DC applications?

A: The SSQ 250, 0679L0250-01, 0451.250MRL, 0453.250MR, and 3404.0006.22 are rated for both 125 V AC and 125 V DC operation. The 0451.250MRSN specification does not explicitly state DC voltage rating; confirmation with the manufacturer is required before use in DC circuits.

Q: What packaging format differences exist among the substitute parts?

A: The SSQ 250, 0679L0250-01, 0451.250MRL, 0451.250MRSN, and 0453.250MR all use 2-SMD, Square End Block package configuration. The 3404.0006.22 uses 2-SMD, J-Lead configuration, which has different lead geometry and requires different PCB pad design.

Q: Which substitute part offers the best supply chain availability?

A: The 0451.250MRL (Littelfuse NANO²® 451 Series) has the highest inventory availability at 20,400 units, followed by 0453.250MR at 10,100 units. The 0679L0250-01 has 7,190 units available. The 0451.250MRSN has limited availability at 813 units.

Q: Do all substitute parts meet RoHS and REACH compliance requirements?

A: All substitute parts listed are ROHS3 Compliant and REACH Unaffected, matching the compliance status of the original SSQ 250.

Q: What approval agencies certify each substitute part?

A: The 0679L0250-01 carries AEC-Q200 and cURus certifications. The 0451.250MRL and 0453.250MR carry CSA and UL certifications. The 0451.250MRSN carries CSA and UR certifications. The 3404.0006.22 carries cURus certification. Verify that the selected substitute's certification aligns with application and regional regulatory requirements.

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