Littelfuse 0451.630MR Surface Mount Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 0451.630MR is a 630 mA, 125 V AC/DC surface mount board fuse in the NANO²® 451 series, featuring a 2-SMD square end block package. This component is classified as obsolete, though 736 pieces remain in stock as new original inventory. Due to its obsolete status, identifying active equivalent and substitute parts is necessary for ongoing design support and production continuity.

Key Parameters

Parameter	Value
Current Rating	630 mA
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
Breaking Capacity @ Rated Voltage	50A
Operating Temperature Range	-55°C ~ 125°C
Size / Dimension	0.240" L x 0.106" W x 0.106" H (6.10mm x 2.69mm x 2.69mm)
Approval Agency	CSA, UL

Substitute Part Grouping Explanation

Substitution eligibility for the 0451.630MR is determined by the following mandatory parameters:

Current Rating: 630 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 / Case: 2-SMD, Square End Block (exact match required)
Breaking Capacity @ Rated Voltage: 50A (exact match required)
Operating Temperature Range: -55°C ~ 125°C (exact match required)
Physical Dimensions: 0.240" L x 0.106" W x 0.106" H (exact match required)
Approval Agency: CSA, UL (exact match required)

All five substitute parts listed below meet these mandatory criteria. Variations in packaging format (Tape & Reel vs. bulk), RoHS compliance status, and DC cold resistance values do not affect functional equivalence for circuit protection applications.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating	Voltage AC/DC	Response Time	Breaking Capacity	Melting I²t	DC Cold Resistance	Product Status	RoHS Status	Packaging
0451.630MR	Littelfuse Inc.	NANO²® 451	630 mA	125 V / 125 V	Fast Blow	50A	0.143	0.305 Ω	Obsolete	RoHS non-compliant	Bulk
0448.630MR	Littelfuse Inc.	NANO²® 448	630 mA	125 V / 125 V	Fast Blow	50A	0.121	0.2821 Ω	Active	ROHS3 Compliant	Tape & Reel (TR)
0451.630MRL	Littelfuse Inc.	NANO²® 451	630 mA	125 V / 125 V	Fast Blow	50A	0.143	0.305 Ω	Active	ROHS3 Compliant	Tape & Reel (TR)
0451.630NRL	Littelfuse Inc.	NANO²® 451	630 mA	125 V / 125 V	Fast Blow	50A	0.143	0.305 Ω	Active	ROHS3 Compliant	Tape & Reel (TR)
0453.630MR	Littelfuse	NANO²® 453	630 mA	125 V / 125 V	Fast Blow	50A	0.143	0.305 Ω	Active	ROHS3 Compliant	Tape & Reel (TR)
0453.630NR	Littelfuse Inc.	NANO²® 453	630 mA	125 V / 125 V	Fast Blow	50A	0.143	0.305 Ω	Active	ROHS3 Compliant	Tape & Reel (TR)

Engineering Selection Recommendations

All five substitute parts are functionally equivalent to the 0451.630MR based on electrical and mechanical parameters. Selection among these alternatives should be based on the following factors:

Product Status: The 0451.630MR is obsolete. All substitute parts listed are active products with ongoing manufacturer support and availability.

RoHS Compliance: The original 0451.630MR is RoHS non-compliant. All substitute parts (0448.630MR, 0451.630MRL, 0451.630NRL, 0453.630MR, 0453.630NR) are ROHS3 compliant, meeting current environmental and regulatory requirements.

Packaging Format: The original part is supplied in bulk packaging. All substitutes are available in Tape & Reel (TR) format, which is standard for automated assembly processes.

Series Variants: Three substitute parts maintain the NANO²® 451 series designation (0451.630MRL, 0451.630NRL), while two are from the NANO²® 448 and NANO²® 453 series. All maintain identical electrical performance and physical dimensions.

Inventory Availability: Substitute parts show significantly higher stock levels, ranging from 811 to 11,231 pieces, compared to 736 pieces of the obsolete original part.

Frequently Asked Questions (FAQ)

Q: Can I directly replace the 0451.630MR with any of these substitute parts?

A: Yes. All five substitute parts meet the mandatory electrical and mechanical parameters: 630 mA current rating, 125 V AC/DC voltage rating, fast blow response, 50A breaking capacity, and identical physical dimensions (0.240" L x 0.106" W x 0.106" H). They are functionally equivalent for circuit protection applications.

Q: What is the difference between the NANO²® 451, 448, and 453 series?

A: The series designation indicates different product generations within Littelfuse's NANO²® fuse family. All three series maintain identical electrical specifications and physical dimensions for the 630 mA, 125 V rating. The primary differences are in manufacturing generation and compliance certifications.

Q: Does the difference in DC cold resistance affect circuit performance?

A: DC cold resistance values (0.305 Ω for most parts, 0.2821 Ω for 0448.630MR) are within acceptable tolerance for circuit protection applications and do not affect the fuse's primary function of overcurrent protection.

Q: Why should I choose a ROHS3 compliant part over the original?

A: ROHS3 compliance ensures the part meets current environmental regulations and is suitable for modern manufacturing processes. The original RoHS non-compliant part may face restrictions in certain markets or applications.

Q: What is the significance of the packaging difference (bulk vs. Tape & Reel)?

A: Tape & Reel packaging is standard for automated surface mount assembly. If your production process uses automated pick-and-place equipment, Tape & Reel format is required. Bulk packaging is suitable for manual assembly or lower-volume applications.

Q: Are all substitute parts certified by CSA and UL?

A: Yes. All substitute parts listed carry CSA and UL approval certifications, meeting the same safety and performance standards as the original 0451.630MR.

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