Littelfuse 0451.375MR Surface Mount Fuse – Equivalent & Substitute Parts

Part Overview

The Littelfuse 0451.375MR is a 375 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, making equivalent substitute parts necessary for ongoing production and maintenance applications. Substitute parts must maintain identical electrical ratings, mechanical dimensions, and approval certifications to ensure direct board-level compatibility.

Key Parameters

Parameter	Value
Current Rating	375 mA
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Fast Blow
Package / Case	2-SMD, Square End Block
Breaking Capacity @ Rated Voltage	50 A
Operating Temperature Range	-55°C to 125°C
Mounting Type	Surface Mount
Approval Agencies	CSA, UL

Substitute Part Grouping Explanation

Substitute parts for the 0451.375MR are classified into two categories based on electrical and mechanical compatibility:

Direct Manufacturer Equivalents (Littelfuse NANO²® Series): Parts 0451.375MRL, 0448.375MR, 0451.375NRL, and 0453.375MR/0453.375NR maintain identical current ratings (375 mA), voltage ratings (125 V AC/DC), response time (Fast Blow), package configuration (2-SMD, Square End Block), breaking capacity (50 A), and operating temperature range (-55°C to 125°C). These parts differ primarily in series designation, packaging format (Tape & Reel vs. bulk), and product status (Active vs. Obsolete). All carry CSA and UL approvals.

Cross-Manufacturer Equivalents (Bourns SinglFuse™ Series): Parts SF-2410FP0375T-2 and SF-2410HI0375T-2 match the same electrical specifications and mechanical footprint. These Bourns components are approved by cUL and UL, meeting the same safety standards as Littelfuse alternatives.

Critical Substitution Parameters:

Current Rating: 375 mA (exact match required)
Voltage Ratings: 125 V AC and 125 V DC (exact match required)
Package / Case: 2-SMD, Square End Block (exact match required)
Breaking Capacity: 50 A (exact match required)
Mounting Type: Surface Mount (exact match required)

Parameter Comparison

Part Number	Manufacturer	Series	Current (mA)	Voltage AC/DC (V)	Response Time	Breaking Capacity (A)	DC Cold Resistance (Ω)	Melting I²t	Product Status	RoHS Status
0451.375MR	Littelfuse	NANO²® 451	375	125/125	Fast Blow	50	0.61	0.0425	Obsolete	Non-compliant
0451.375MRL	Littelfuse	NANO²® 451	375	125/125	Fast Blow	50	0.61	0.0425	Active	ROHS3 Compliant
0448.375MR	Littelfuse	NANO²® 448	375	125/125	Fast Blow	50	0.73	0.024	Active	ROHS3 Compliant
0451.375NRL	Littelfuse	NANO²® 451	375	125/125	Fast Blow	50	0.61	0.0425	Active	ROHS3 Compliant
0453.375MR	Littelfuse	NANO²® 453	375	125/125	Fast Blow	50	0.61	0.0425	Active	ROHS3 Compliant
0453.375NR	Littelfuse	NANO²® 453	375	125/125	Fast Blow	50	0.61	0.0425	Active	ROHS3 Compliant
SF-2410FP0375T-2	Bourns	SinglFuse™ SF-2410FP-T	375	125/125	Fast Blow	50	0.732	0.1502	Active	ROHS3 Compliant
SF-2410HI0375T-2	Bourns	SinglFuse™ SF-2410HI-T	375	125/125	Fast Blow	50	0.6208	0.4147	Active	ROHS3 Compliant

Engineering Selection Recommendations

For applications currently using the obsolete 0451.375MR, the following selection criteria apply:

Primary Recommendation: 0451.375MRL (Littelfuse NANO²® 451 series, Tape & Reel packaging). This part is an exact electrical and mechanical equivalent with Active product status and ROHS3 compliance. It maintains identical DC cold resistance (0.61 Ω) and melting I²t (0.0425), ensuring identical thermal response characteristics.

Alternative Littelfuse Options: 0451.375NRL, 0453.375MR, and 0453.375NR are functionally equivalent with Active status and full RoHS3 compliance. These parts differ only in series designation and packaging format. All maintain the critical electrical parameters required for direct substitution.

Secondary Option (Different Series): 0448.375MR (NANO²® 448 series) is electrically compatible but exhibits higher DC cold resistance (0.73 Ω) and lower melting I²t (0.024) compared to the original part. This part is suitable only when thermal response variations are acceptable within system design margins.

Cross-Manufacturer Alternative: Bourns SF-2410FP0375T-2 and SF-2410HI0375T-2 provide equivalent electrical and mechanical performance with cUL and UL certifications. These parts differ in melting I²t characteristics (0.1502 and 0.4147 respectively) and should be selected based on specific thermal response requirements. SF-2410HI0375T-2 carries REACH Affected status, requiring compliance verification for regulated applications.

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

Frequently Asked Questions (FAQ)

Q: Can I use 0451.375MRL as a direct replacement for 0451.375MR?

A: Yes. The 0451.375MRL is an exact electrical and mechanical equivalent with identical current rating (375 mA), voltage ratings (125 V AC/DC), response time (Fast Blow), package configuration (2-SMD, Square End Block), and breaking capacity (50 A). The primary difference is product status (Active vs. Obsolete) and packaging format (Tape & Reel). Both parts carry CSA and UL approvals.

Q: What is the difference between Littelfuse NANO²® series variants (451, 448, 453)?

A: All three series maintain identical electrical ratings and mechanical dimensions for the 375 mA, 125 V specification. Series differences reflect internal design variations. The 0448.375MR exhibits different DC cold resistance (0.73 Ω vs. 0.61 Ω) and melting I²t (0.024 vs. 0.0425), which may affect thermal response in sensitive applications. The 451 and 453 series maintain identical thermal characteristics.

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

A: Bourns SF-2410FP0375T-2 and SF-2410HI0375T-2 are mechanically and electrically compatible for the 375 mA, 125 V AC/DC specification. Both carry cUL and UL approvals. However, melting I²t values differ significantly (0.1502 and 0.4147 respectively compared to 0.0425 for NANO²® 451/453), affecting thermal response characteristics. Selection should account for system-specific thermal requirements.

Q: What does "Tape & Reel (TR)" packaging mean?

A: Tape & Reel packaging is a continuous strip format used for automated assembly processes. The original 0451.375MR was supplied in bulk form. Equivalent parts with TR designation (0451.375MRL, 0448.375MR, 0451.375NRL, 0453.375MR, 0453.375NR, SF-2410FP0375T-2, SF-2410HI0375T-2) are supplied on continuous tape reels, optimized for pick-and-place manufacturing. Electrical and mechanical specifications remain identical.

Q: Why is RoHS compliance important for fuse selection?

A: RoHS3 compliance indicates the part meets current environmental and hazardous substance restrictions. The original 0451.375MR is RoHS non-compliant (obsolete status). All active substitute parts listed are ROHS3 compliant, ensuring compliance with current procurement and environmental regulations. This is particularly important for new designs and regulated applications.

Q: Can I mix different substitute parts on the same board?

A: Yes, provided all parts meet the identical electrical specifications (375 mA, 125 V AC/DC, Fast Blow, 50 A breaking capacity) and mechanical requirements (2-SMD, Square End Block package). However, mixing parts with different melting I²t values (such as combining NANO²® 451 with SF-2410HI0375T-2) may result in inconsistent thermal response across the board. For critical applications, use a single part number throughout.

Q: What is the significance of DC Cold Resistance variation?

A: DC cold resistance affects the voltage drop across the fuse during normal operation. The original 0451.375MR and most NANO²® equivalents maintain 0.61 Ω. The 0448.375MR exhibits 0.73 Ω, resulting in higher voltage drop. Bourns parts range from 0.6208 Ω to 0.732 Ω. For applications with tight voltage budgets or high current density, verify that resistance variations remain within system design margins.

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