Equivalent & Substitute Parts for 0451003.MR

Part Overview

The Littelfuse 0451003.MR is a 3 A, 125 V AC/DC surface mount board mount fuse in the NANO²® 451 series, packaged as a 2-SMD square end block component. This part is classified as obsolete, making identification of active equivalent and substitute parts essential for ongoing design support and procurement continuity. Equivalent parts maintain identical electrical and mechanical specifications, while substitute parts offer functional compatibility within the defined parameter envelope.

Key Parameters

Parameter	Value
Current Rating	3 A
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
Breaking Capacity @ Rated Voltage	50 A
Operating Temperature Range	-55°C to 125°C
Size / Dimension	0.240" L x 0.106" W x 0.106" H (6.10mm x 2.69mm x 2.69mm)

Substitute Part Grouping Explanation

Substitution eligibility for the 0451003.MR is determined by strict equivalence across the following parameters:

Current Rating: 3 A (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: 50 A (exact match required)
Operating Temperature Range: -55°C to 125°C (exact match required)
Physical Dimensions: 0.240" L x 0.106" W x 0.106" H (exact match required)

All listed substitute parts meet these criteria. Littelfuse parts (0448003.MR, 0451003.MRL, 0451003.NRL, 0453003.MR, 0453003.NR) are from the same manufacturer with identical electrical specifications. Bourns parts (SF-2410FP300T-2, SF-2410HI300T-2) are cross-manufacturer equivalents meeting all functional and dimensional requirements.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating	Voltage (AC/DC)	Response Time	Melting I²t	DC Cold Resistance (Ohms)	Product Status	RoHS Status	Packaging
0451003.MR	Littelfuse Inc.	NANO²® 451	3 A	125 V / 125 V	Fast Blow	1.65	0.0227	Obsolete	RoHS non-compliant	-
0448003.MR	Littelfuse Inc.	NANO²® 448	3 A	125 V / 125 V	Fast Blow	1.72	0.02445	Active	ROHS3 Compliant	Cut Tape (CT) & Digi-Reel®
0451003.MRL	Littelfuse Inc.	NANO²® 451	3 A	125 V / 125 V	Fast Blow	1.65	0.0227	Active	ROHS3 Compliant	Cut Tape (CT) & Digi-Reel®
0451003.NRL	Littelfuse Inc.	NANO²® 451	3 A	125 V / 125 V	Fast Blow	1.65	0.0227	Active	ROHS3 Compliant	Tape & Reel (TR)
0453003.MR	Littelfuse Inc.	NANO²® 453	3 A	125 V / 125 V	Fast Blow	1.65	0.0227	Active	ROHS3 Compliant	Tape & Reel (TR)
0453003.NR	Littelfuse Inc.	NANO²® 453	3 A	125 V / 125 V	Fast Blow	1.65	0.0227	Active	ROHS3 Compliant	Tape & Reel (TR)
SF-2410FP300T-2	Bourns Inc.	SinglFuse™ SF-2410FP-T	3 A	125 V / 125 V	Fast Blow	1.548	0.036	Active	ROHS3 Compliant	Tape & Reel (TR)
SF-2410HI300T-2	Bourns Inc.	SinglFuse™ SF-2410HI-T	3 A	125 V / 125 V	Fast Blow	24.99	0.0228	Active	ROHS3 Compliant	Tape & Reel (TR)

Engineering Selection Recommendations

For applications currently using the obsolete 0451003.MR, the following selection criteria apply:

Littelfuse NANO²® Series (Recommended for Direct Replacement): Parts 0451003.MRL, 0451003.NRL, 0453003.MR, and 0453003.NR are active Littelfuse equivalents with identical electrical characteristics and ROHS3 compliance. These parts maintain the same melting I²t (1.65) and DC cold resistance (0.0227 Ohms) as the original part. Selection between these options depends on packaging requirements: 0451003.MRL and 0451003.NRL are from the same NANO²® 451 series; 0453003.MR and 0453003.NR are from the NANO²® 453 series with equivalent performance.

Littelfuse NANO²® 448 (0448003.MR): This active part offers ROHS3 compliance with marginally higher melting I²t (1.72) and DC cold resistance (0.02445 Ohms). It is functionally equivalent within the defined parameter envelope.

Bourns SinglFuse™ Series (Cross-Manufacturer Alternative): Parts SF-2410FP300T-2 and SF-2410HI300T-2 are active cross-manufacturer equivalents with identical current, voltage, and response time ratings. Both are ROHS3 compliant. The SF-2410FP300T-2 has lower melting I²t (1.548) and higher DC cold resistance (0.036 Ohms). The SF-2410HI300T-2 has significantly higher melting I²t (24.99), indicating slower response characteristics, and is subject to REACH regulations.

All substitute parts maintain the 50 A breaking capacity, -55°C to 125°C operating temperature range, and identical 2-SMD square end block package dimensions.

Frequently Asked Questions (FAQ)

Q: Can I use 0451003.MRL as a direct replacement for the obsolete 0451003.MR?

A: Yes. The 0451003.MRL is an active equivalent from the same NANO²® 451 series with identical electrical specifications (3 A, 125 V AC/DC, fast blow response, 1.65 melting I²t, 0.0227 Ohms DC cold resistance). The primary difference is packaging format and ROHS3 compliance status.

Q: What is the difference between Littelfuse NANO²® 451 and 453 series parts?

A: Both series meet the electrical and mechanical requirements for substitution. The 451 series (0451003.MRL, 0451003.NRL) and 453 series (0453003.MR, 0453003.NR) are functionally equivalent with identical melting I²t and DC cold resistance values. Selection depends on packaging availability and procurement logistics.

Q: Are Bourns SinglFuse™ parts fully compatible with Littelfuse NANO²® parts?

A: Yes, within the defined parameter envelope. Both SF-2410FP300T-2 and SF-2410HI300T-2 meet the 3 A, 125 V AC/DC, fast blow, 50 A breaking capacity, and 2-SMD square end block package requirements. However, they differ in melting I²t characteristics: SF-2410FP300T-2 has lower I²t (1.548), while SF-2410HI300T-2 has significantly higher I²t (24.99), affecting response speed.

Q: What packaging options are available for active equivalents?

A: Littelfuse parts are available in Cut Tape (CT) & Digi-Reel® (0451003.MRL, 0448003.MR) and Tape & Reel (TR) formats (0451003.NRL, 0453003.MR, 0453003.NR). Bourns parts are supplied in Tape & Reel (TR) format only.

Q: Does the 0451003.MR have RoHS compliance?

A: No. The 0451003.MR is RoHS non-compliant. All active substitute parts (Littelfuse NANO²® 448, 451, 453 series and Bourns SinglFuse™ series) are ROHS3 compliant.

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

A: Melting I²t determines the thermal energy required to melt the fuse element and is critical for coordination with circuit protection schemes. The 0451003.MR has melting I²t of 1.65. Most Littelfuse equivalents maintain this value. The Bourns SF-2410FP300T-2 has lower I²t (1.548), while SF-2410HI300T-2 has significantly higher I²t (24.99), indicating different response characteristics.

Q: Are there inventory considerations for part selection?

A: Yes. Current inventory levels vary: 0453003.MR has the highest stock (56,556 pcs), followed by 0451003.MRL (30,200 pcs). Lower inventory parts include 0451003.NRL (10,263 pcs), 0448003.MR (17,025 pcs), SF-2410HI300T-2 (3,392 pcs), SF-2410FP300T-2 (2,631 pcs), and 0453003.NR (668 pcs).

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