Littelfuse 0451.400MRSN Surface Mount Board Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 0451.400MRSN is a 400 mA, 125 V AC surface mount board fuse in the NANO²® 451 series. This fast-blow fuse is designed for board-level circuit protection in applications requiring compact, high-reliability protection. The part is active in production with full inventory availability. Equivalent and substitute parts are identified based on matching electrical ratings, mechanical dimensions, and package specifications to ensure direct functional replacement in circuit designs.

Substiute Parts

0451.400MRSN

Littelfuse Inc.In Stock: 10810451.400MRSN Datasheet

Current PartRFQ

0448.400MR

Littelfuse Inc.In Stock: 61620448.400MR Datasheet

Parametric EquivalentRFQ

0451.400MRL

Littelfuse Inc.In Stock: 770900451.400MRL Datasheet

Parametric EquivalentRFQ

0453.400MR

Littelfuse Inc.In Stock: 134280453.400MR Datasheet

Parametric EquivalentRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the 0451.400MRSN are qualified based on the following critical parameters:

• Current Rating: 400 mA (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 / 6.10mm x 2.69mm x 2.69mm (exact match required)
• Response Time: Fast Blow (exact match required)
• Breaking Capacity: 50A (exact match required)
• Operating Temperature Range: -55°C ~ 125°C (exact match required)
• RoHS Compliance: ROHS3 Compliant (exact match required)

All substitute parts listed maintain these critical electrical and mechanical specifications, ensuring functional equivalence in circuit protection applications.

Parameter Comparison

Engineering Selection Recommendations

All substitute parts listed—0448.400MR, 0451.400MRL, and 0453.400MR—are active production components from Littelfuse Inc. with full RoHS3 compliance and regulatory approvals. Selection among these equivalents should be based on:

Approval Agency Alignment: The main part 0451.400MRSN carries CSA and UR approvals. Substitute parts 0448.400MR, 0451.400MRL, and 0453.400MR carry CSA and UL approvals. Verify that the target application's regulatory requirements align with the applicable certification body.

DC Voltage Rating: The main part 0451.400MRSN specifies 125 V AC only. All substitute parts provide dual AC/DC ratings at 125 V, offering expanded application flexibility for designs requiring DC circuit protection.

Melting I²t and DC Cold Resistance: Minor variations exist in thermal and resistance characteristics. The 0451.400MRL exhibits the lowest DC cold resistance (0.4233 Ohms), while the 0448.400MR shows the lowest melting I²t (0.0416). These differences are within the tolerance band for equivalent circuit protection performance at the 400 mA rating.

Inventory Availability: The 0451.400MRL offers the highest stock level (77,055 pcs), followed by 0448.400MR (6,144 pcs) and 0453.400MR (13,350 pcs), supporting supply chain continuity.

Frequently Asked Questions (FAQ)

Q: Can the 0448.400MR, 0451.400MRL, and 0453.400MR be used interchangeably with the 0451.400MRSN?

A: Yes. All substitute parts match the critical electrical parameters (400 mA, 125 V AC, fast-blow response), mechanical dimensions (0.240" x 0.106" x 0.106"), and package specification (2-SMD, Square End Block). They are functionally equivalent for board-level circuit protection applications.

Q: What is the difference between the main part and the substitutes in terms of voltage rating?

A: The 0451.400MRSN is rated for 125 V AC only. The substitute parts (0448.400MR, 0451.400MRL, 0453.400MR) are rated for both 125 V AC and 125 V DC. This makes the substitutes suitable for both AC and DC circuit protection, providing design flexibility.

Q: Are there differences in thermal characteristics between these parts?

A: Minor variations exist in melting I²t and DC cold resistance. The 0451.400MRL has a DC cold resistance of 0.4233 Ohms, while the 0451.400MRSN and 0453.400MR are rated at 0.56 Ohms. The 0448.400MR has a melting I²t of 0.0416 compared to 0.0484 for the others. These differences do not affect functional equivalence at the 400 mA rating.

Q: Do all parts have the same regulatory approvals?

A: The main part carries CSA and UR approvals. The substitute parts carry CSA and UL approvals. Both certification paths meet industry standards; however, verify that your application's regulatory requirements align with the applicable certification body.

Q: Are all parts RoHS compliant?

A: Yes. All parts listed are ROHS3 compliant and suitable for applications requiring environmental compliance.

Q: What is the operating temperature range for these fuses?

A: All parts operate across the range of -55°C to 125°C, ensuring performance in standard industrial and commercial temperature environments.

Q: Can these parts be used in both AC and DC circuits?

A: The 0451.400MRSN is rated for AC circuits only (125 V AC). The substitute parts (0448.400MR, 0451.400MRL, 0453.400MR) are rated for both AC and DC circuits (125 V AC / 125 V DC), making them suitable for broader application requirements.