Littelfuse 0451.250MR Surface Mount Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 0451.250MR is a 250 mA, 125 V AC/DC surface mount board fuse in the NANO²® 451 series with a 2-SMD square end block package. This part is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production requirements. Substitute parts maintain identical electrical ratings and mechanical dimensions while offering improved availability and compliance status.

Key Parameters

Parameter	Value
Current Rating	250 mA
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Fast Blow
Package Type	2-SMD, Square End Block
Mounting Type	Surface Mount
Breaking Capacity	50 A @ Rated Voltage
Operating Temperature Range	-55°C to 125°C
Physical Dimensions	0.240" L × 0.106" W × 0.106" H (6.10mm × 2.69mm × 2.69mm)
Approval Agencies	CSA, UL

Substitute Part Grouping Explanation

Substitute parts for the 0451.250MR are classified based on the following substitution criteria:

Electrical Parameters (Must Match):

Current Rating: 250 mA
Voltage Rating: 125 V AC / 125 V DC
Response Time: Fast Blow
Breaking Capacity: 50 A @ Rated Voltage

Mechanical Parameters (Must Match):

Package Type: 2-SMD, Square End Block
Physical Dimensions: 0.240" L × 0.106" W × 0.106" H
Mounting Type: Surface Mount

Allowed Variations:

Series designation (NANO²® 451, NANO²® 453, NANO²® 448, or alternative manufacturer)
Packaging format (Tube or Tape & Reel)
Product status (Active preferred over Obsolete)
RoHS and REACH compliance status
DC Cold Resistance (within acceptable tolerance for fast-blow fuse operation)
Melting I²t (minor variations acceptable for same response class)

Parameter Comparison

Part Number	Manufacturer	Series	Current (mA)	Voltage AC/DC (V)	Response	Package	Status	RoHS	DC Resistance (Ω)	Melting I²t
0451.250MR	Littelfuse	NANO²® 451	250	125/125	Fast Blow	2-SMD Square	Obsolete	Non-compliant	0.5765	0.0158
0453.250MR	Littelfuse	NANO²® 453	250	125/125	Fast Blow	2-SMD Square	Active	ROHS3 Compliant	0.5765	0.0158
0448.250MR	Littelfuse	NANO²® 448	250	125/125	Fast Blow	2-SMD Square	Active	ROHS3 Compliant	1.05	0.0152
0451.250MRL	Littelfuse	NANO²® 451	250	125/125	Fast Blow	2-SMD Square	Active	ROHS3 Compliant	0.5765	0.0158
0451.250NRL	Littelfuse	NANO²® 451	250	125/125	Fast Blow	2-SMD Square	Active	ROHS3 Compliant	0.5765	0.0158
0453.250NR	Littelfuse	NANO²® 453	250	125/125	Fast Blow	2-SMD Square	Active	ROHS3 Compliant	0.5765	0.0158
SF-2410FP025T-2	Bourns Inc.	SinglFuse™ SF-2410FP-T	250	125/125	Fast Blow	2-SMD Square	Active	ROHS3 Compliant	1.119	0.0528

Engineering Selection Recommendations

Primary Recommendation: Littelfuse 0453.250MR

The 0453.250MR is the manufacturer-recommended direct substitute. It maintains identical electrical and mechanical specifications to the 0451.250MR while offering active product status and ROHS3 compliance. This part is available in Tape & Reel packaging with 10,100 units in stock.

Secondary Recommendations: Littelfuse 0451.250MRL and 0451.250NRL

Both parts are from the same NANO²® 451 series as the original component and maintain identical electrical characteristics (DC resistance 0.5765 Ω, Melting I²t 0.0158). These parts offer active status and ROHS3 compliance. The 0451.250MRL has the highest inventory availability at 20,400 units.

Alternative Recommendation: Littelfuse 0453.250NR

The 0453.250NR provides parametric equivalence with identical electrical ratings and DC resistance. It is available in Tape & Reel format with 3,700 units in stock and carries active product status with ROHS3 compliance.

Cross-Manufacturer Alternative: Bourns SF-2410FP025T-2

The Bourns SinglFuse™ SF-2410FP025T-2 meets all electrical and mechanical requirements with identical current, voltage, and breaking capacity ratings. This part carries cUL and UL approvals and ROHS3 compliance. Note that DC cold resistance (1.119 Ω) and melting I²t (0.0528) differ from the Littelfuse options; however, these variations remain within acceptable parameters for fast-blow fuse operation at the specified current and voltage ratings.

Littelfuse 0448.250MR Consideration

The 0448.250MR from the NANO²® 448 series meets all electrical and mechanical specifications. DC cold resistance is elevated at 1.05 Ω compared to 0.5765 Ω in the original part, and melting I²t is slightly lower at 0.0152 versus 0.0158. This part is active and ROHS3 compliant with 10,200 units available.

Frequently Asked Questions (FAQ)

Q: Can I use 0453.250MR as a direct replacement for 0451.250MR?

A: Yes. The 0453.250MR is the manufacturer-recommended substitute. Both parts share identical electrical ratings (250 mA, 125 V AC/DC, Fast Blow response), mechanical dimensions (0.240" × 0.106" × 0.106"), and package type (2-SMD square end block). The primary difference is product status: 0451.250MR is obsolete while 0453.250MR is active with ROHS3 compliance.

Q: What is the difference between 0451.250MRL and 0451.250MR?

A: The primary difference is packaging format. The 0451.250MR is supplied in tube packaging, while 0451.250MRL is supplied in Tape & Reel format. Electrical and mechanical specifications are identical. The 0451.250MRL also carries active product status and ROHS3 compliance compared to the obsolete status of the original part.

Q: Can I substitute the Bourns SF-2410FP025T-2 for the Littelfuse 0451.250MR?

A: Yes, with the understanding that DC cold resistance and melting I²t values differ. The Bourns part maintains the same current rating (250 mA), voltage rating (125 V AC/DC), response time (Fast Blow), breaking capacity (50 A), and physical dimensions. Both parts carry UL/cUL approvals and ROHS3 compliance. The resistance and I²t variations are acceptable for fast-blow fuse operation at the specified ratings.

Q: Why do some substitute parts have different DC cold resistance values?

A: DC cold resistance variations occur across different fuse series and manufacturers due to design differences in the fusible element and internal construction. For fast-blow fuses operating at 250 mA with 125 V ratings, these variations remain within acceptable operating parameters. All listed substitutes maintain the same response time classification and breaking capacity.

Q: Are all substitute parts ROHS3 compliant?

A: All active substitute parts listed (0453.250MR, 0451.250MRL, 0451.250NRL, 0453.250NR, and SF-2410FP025T-2) are ROHS3 compliant. The original 0451.250MR is RoHS non-compliant due to its obsolete status. The 0448.250MR is also ROHS3 compliant.

Q: What is the difference between Tape & Reel (TR) and tube packaging?

A: Tape & Reel packaging is used for automated assembly processes and provides parts wound on a continuous tape with a reel for pick-and-place equipment. Tube packaging is used for manual assembly or lower-volume applications. Electrical and mechanical specifications remain identical regardless of packaging format.

Q: Can I mix different substitute parts in the same design?

A: Yes. All listed substitutes meet identical electrical and mechanical specifications for the 250 mA, 125 V AC/DC fast-blow fuse application. However, for consistency in production and inventory management, selecting a single substitute part is recommended.

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