Littelfuse 0251001.NRT2 Equivalent & Substitute Parts

Part Overview

The Littelfuse 0251001.NRT2 is a 1 A, 125 V AC/DC board mount axial fuse from the PICO® II 251 series. This component is classified as obsolete, which necessitates identification of active equivalent parts for ongoing design and procurement requirements. The part maintains fast-blow response characteristics with a 50 A AC / 300 A DC breaking capacity and operates across the temperature range of -55°C to 125°C. Equivalent active parts are available with identical electrical and mechanical specifications, differing primarily in packaging configuration and compliance status.

Key Parameters

Parameter	Specification
Current Rating	1 A
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Fast Blow
Mounting Type	Through Hole
Fuse Type	Board Mount (Cartridge Style Excluded)
Package / Case	Axial
Breaking Capacity @ Rated Voltage	50 A AC, 300 A DC
Melting I²t	0.256
Size / Dimension	0.110" Dia x 0.280" L (2.80 mm x 7.11 mm)
DC Cold Resistance	0.128 Ohms
Operating Temperature Range	-55°C to 125°C
Approval Agencies	CCC, CSA, cURus, PSE, TUV

Substitute Part Grouping Explanation

Substitution of the obsolete 0251001.NRT2 is determined by strict equivalence across the following critical parameters:

Current Rating: 1 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: Through Hole (exact match required)
Package / Case: Axial (exact match required)
Physical Dimensions: 0.110" Dia x 0.280" L (exact match required)
Breaking Capacity: 50 A AC, 300 A DC (exact match required)
Melting I²t: 0.256 (exact match required)
DC Cold Resistance: 0.128 Ohms (exact match required)
Series: PICO® II 251 (exact match required)

All substitute parts listed maintain identical electrical performance and mechanical compatibility. Differences exist only in packaging format (Bulk, Cut Tape, Tape & Reel) and product status (Active vs. Obsolete). The primary distinction between the main part and substitutes is RoHS compliance status: the obsolete 0251001.NRT2 is RoHS non-compliant, while all active equivalents are ROHS3 compliant.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating	Voltage AC/DC	Response Time	Breaking Capacity	Melting I²t	Packaging	Product Status	RoHS Status
0251001.NRT2	Littelfuse	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	-	Obsolete	RoHS non-compliant
0251001.MXL	Littelfuse	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	Bulk	Active	ROHS3 Compliant
0251001.HAT1L	Littelfuse Inc.	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	Cut Tape (CT)	Active	ROHS3 Compliant
0251001.MAT1L	Littelfuse Inc.	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	Cut Tape (CT)	Active	ROHS3 Compliant
0251001.MRT1L	Littelfuse Inc.	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	Cut Tape (CT)	Active	ROHS3 Compliant
0251001.NAT1L	Littelfuse	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	Cut Tape (CT)	Active	ROHS3 Compliant
0251001.NRT1L	Littelfuse Inc.	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	Cut Tape (CT)	Active	ROHS3 Compliant
0251001.PARL	Littelfuse Inc.	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	Tape & Reel (TR)	Active	ROHS3 Compliant
0251001.PAT1L	Littelfuse Inc.	PICO® II 251	1 A	125 V / 125 V	Fast Blow	50 A AC, 300 A DC	0.256	Cut Tape (CT)	Active	ROHS3 Compliant
0491001.MAT1	Littelfuse Inc.	PICO® II 491	1 A	125 V / 125 V	Fast Blow	50 A AC	0.256	-	Active	ROHS3 Compliant

Engineering Selection Recommendations

For replacement of the obsolete 0251001.NRT2, selection among active equivalents should be based on procurement requirements and compliance mandates:

Primary Recommendation: Parts from the PICO® II 251 series (0251001.MXL, 0251001.HAT1L, 0251001.MAT1L, 0251001.MRT1L, 0251001.NAT1L, 0251001.NRT1L, 0251001.PARL, 0251001.PAT1L) are direct electrical and mechanical equivalents with identical performance characteristics. All are ROHS3 compliant and carry active product status. Selection among these parts should be determined by packaging requirements: Bulk (0251001.MXL) for large-volume procurement, Cut Tape (0251001.HAT1L, 0251001.MAT1L, 0251001.MRT1L, 0251001.NAT1L, 0251001.NRT1L, 0251001.PAT1L) for standard component handling, or Tape & Reel (0251001.PARL) for automated assembly processes.

Alternative Consideration: The 0491001.MAT1 from the PICO® II 491 series maintains identical electrical specifications and physical dimensions but differs in breaking capacity (50 A AC only, without 300 A DC specification) and approval agency certifications (CSA, PSE, UL versus CCC, CSA, cURus, PSE, TUV). This part is suitable only when DC breaking capacity specification is not required and the reduced certification set is acceptable for the application.

Frequently Asked Questions (FAQ)

Q: Can 0251001.NRT2 be directly replaced with any of the listed substitutes?

A: Yes. All PICO® II 251 series parts (0251001.MXL, 0251001.HAT1L, 0251001.MAT1L, 0251001.MRT1L, 0251001.NAT1L, 0251001.NRT1L, 0251001.PARL, 0251001.PAT1L) are direct replacements with identical electrical performance, mechanical dimensions, and breaking capacity. The 0491001.MAT1 is electrically equivalent but has reduced breaking capacity specification and different certifications.

Q: What is the difference between the packaging options?

A: Packaging differences do not affect electrical or mechanical performance. Bulk packaging (0251001.MXL) is supplied loose for manual handling. Cut Tape (CT) packaging provides components on adhesive tape for standard component feeders. Tape & Reel (TR) packaging (0251001.PARL) is optimized for automated pick-and-place assembly equipment.

Q: Why is the obsolete 0251001.NRT2 listed as RoHS non-compliant while all active substitutes are ROHS3 compliant?

A: RoHS compliance status reflects manufacturing standards at the time of production. The obsolete part predates current RoHS3 requirements. All active equivalents are manufactured to current ROHS3 standards, ensuring compliance with modern regulatory requirements for new designs and procurement.

Q: Are there any electrical performance differences between the PICO® II 251 and PICO® II 491 series?

A: The PICO® II 251 and PICO® II 491 series maintain identical current rating, voltage rating, response time, melting I²t, and physical dimensions. The primary difference is breaking capacity: PICO® II 251 specifies 50 A AC and 300 A DC, while PICO® II 491 specifies 50 A AC only. Additionally, approval agency certifications differ between the series.

Q: Can packaging format be changed during procurement without affecting circuit performance?

A: Packaging format does not affect electrical or mechanical performance. Selection should be based on assembly process requirements and inventory management practices. All packaging formats of the same part number deliver identical component specifications.

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