Littelfuse 045202.5MRSN Surface Mount Board Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 045202.5MRSN is a 2.5 A, 125 V AC surface mount board fuse in the NANO²® 452 series. This slow-blow fuse is designed for board-level protection in applications requiring cartridge-style excluded board mount configurations. The part is currently active in production with 997 pieces in stock. Substitute parts are identified when equivalent electrical and mechanical parameters are required due to inventory constraints, design revisions, or supply chain considerations.

Key Parameters

Parameter	Value
Current Rating	2.5 A
Voltage Rating (AC)	125 V
Response Time	Slow Blow
Mounting Type	Surface Mount
Package / Case	2-SMD, Square End Block
Physical Dimensions	0.240" L x 0.106" W x 0.106" H (6.10mm x 2.69mm x 2.69mm)
Breaking Capacity	50 A @ Rated Voltage
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 045202.5MRSN is determined by strict equivalence across the following parameters:

Current Rating: 2.5 A (exact match required)
Voltage Rating (AC): 125 V (exact match required)
Mounting Type: Surface Mount (exact match required)
Package / Case: 2-SMD, Square End Block (exact match required)
Physical Dimensions: 0.240" L x 0.106" W x 0.106" H (exact match required)
Response Time: Slow Blow (exact match required)
Breaking Capacity: 50 A @ Rated Voltage (exact match required)
Operating Temperature Range: -55°C to 125°C (exact match required)
RoHS Compliance: ROHS3 Compliant (exact match required)

All four substitute parts meet these criteria. Variations in DC voltage rating, melting I²t values, DC cold resistance, and approval agency certifications do not disqualify substitution when AC parameters and mechanical specifications are identical.

Parameter Comparison

Part Number	Series	Current Rating	Voltage (AC)	Voltage (DC)	Response Time	Package	Dimensions	Breaking Capacity	Melting I²t	DC Cold Resistance	Inventory	Status
045202.5MRSN	NANO²® 452	2.5 A	125 V	—	Slow Blow	2-SMD, Square End Block	0.240" x 0.106" x 0.106"	50 A	15	0.045 Ω	997 Pcs	Active
044902.5MR	NANO²® 449	2.5 A	125 V	125 V	Slow Blow	2-SMD, Square End Block	0.240" x 0.106" x 0.106"	50 A	13.18	0.04 Ω	3800 Pcs	Active
045202.5MRL	NANO²® 452	2.5 A	125 V	125 V	Slow Blow	2-SMD, Square End Block	0.240" x 0.106" x 0.106"	50 A	15	0.045 Ω	15300 Pcs	Active
045202.5NRL	NANO²® 452	2.5 A	125 V	125 V	Slow Blow	2-SMD, Square End Block	0.240" x 0.106" x 0.106"	50 A	15	0.045 Ω	3359 Pcs	Active
045402.5MR	NANO²® 454	2.5 A	125 V	125 V	Slow Blow	2-SMD, Square End Block	0.240" x 0.106" x 0.106"	50 A	15	0.045 Ω	4400 Pcs	Active

Engineering Selection Recommendations

All substitute parts are manufactured by Littelfuse Inc. and maintain active product status. Selection among the four equivalents should be based on the following factors:

Inventory Availability: Part 045202.5MRL offers the highest stock level at 15,300 pieces, followed by 045402.5MR at 4,400 pieces, 044902.5MR at 3,800 pieces, and 045202.5NRL at 3,359 pieces.

Certification Coverage: The main part 045202.5MRSN carries CSA, METI, and UR approvals. Substitute 045202.5MRL maintains CSA, PSE, and UR certifications. Substitute 045402.5MR carries CSA, PSE, and UL certifications. Substitute 044902.5MR holds cULus and PSE certifications. Substitute 045202.5NRL carries CSA, PSE, and UR certifications. Verify that the selected substitute meets all required regulatory approvals for your application.

DC Voltage Capability: The main part 045202.5MRSN is rated for AC only. All four substitutes provide dual AC/DC rating at 125 V, offering expanded application flexibility.

Thermal Characteristics: Parts 045202.5MRL, 045202.5NRL, and 045402.5MR maintain identical melting I²t and DC cold resistance values to the main part. Part 044902.5MR exhibits slightly lower melting I²t (13.18 versus 15) and lower DC cold resistance (0.04 Ω versus 0.045 Ω).

Frequently Asked Questions (FAQ)

Q: Can 045202.5MRL be used as a direct replacement for 045202.5MRSN?

A: Yes. Both parts share identical current rating (2.5 A), AC voltage rating (125 V), response time (Slow Blow), package configuration (2-SMD, Square End Block), physical dimensions, breaking capacity (50 A), melting I²t (15), and DC cold resistance (0.045 Ω). The primary difference is that 045202.5MRL adds DC voltage rating (125 V) and carries different regulatory certifications (CSA, PSE, UR versus CSA, METI, UR).

Q: What is the difference between the NANO²® 452 and NANO²® 454 series?

A: Both series maintain identical electrical and mechanical specifications for the 2.5 A, 125 V configuration. The series designation reflects internal design evolution within the Littelfuse product line. Substitution between series is permissible when all specified parameters match.

Q: Why does 044902.5MR have a lower melting I²t value?

A: The melting I²t value (13.18 for 044902.5MR versus 15 for other parts) reflects thermal characteristics specific to the NANO²® 449 series design. Despite this difference, the part maintains the same current rating, voltage rating, response time classification, and breaking capacity, making it electrically equivalent for board-level protection applications.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All parts listed, including the main part 045202.5MRSN and all four substitutes, are ROHS3 compliant with Moisture Sensitivity Level 1 (Unlimited) and REACH Unaffected status.

Q: Can I use a substitute with DC voltage rating in an AC-only application?

A: Yes. Parts rated for both AC and DC voltage can be used in AC-only applications. The AC voltage rating remains the controlling specification for AC circuits. The additional DC rating does not compromise AC performance.

Q: What packaging format is used for these parts?

A: All parts are supplied in Tape & Reel (TR) format, standard for surface mount board assembly operations.

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