MQ 4.6 Equivalent & Substitute Parts

Part Overview

The MQ 4.6 is a 4.6 A board mount axial fuse rated for 125 V AC/DC operation, manufactured by Bel Fuse Inc. This component is classified as obsolete, making equivalent substitute parts necessary for new designs and ongoing production requirements. The MQ 4.6 maintains fast-blow response characteristics suitable for circuit protection applications requiring precise current limiting at 4.6 amperes.

Key Parameters

Parameter	Value
Current Rating	4.6 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
Operating Temperature Range	-55°C ~ 125°C

Substitute Part Grouping Explanation

Substitution for the MQ 4.6 is determined by strict equivalence across the following electrical and mechanical parameters:

Current Rating: 4.6 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)
Fuse Type: Board Mount, Axial configuration (exact match required)
Breaking Capacity: 50 A AC, 300 A DC (exact match required)
Operating Temperature: -55°C ~ 125°C (exact match required)

The substitute parts identified—025104.6MXL and 025104.6NRT1L, both from Littelfuse Inc. PICO® II 251 series—meet all electrical and mechanical equivalence criteria. Differences in physical dimensions (diameter and length tolerances) and DC cold resistance remain within acceptable engineering variance for this product category. Packaging format (Bulk vs. Cut Tape) represents a procurement variable rather than a functional substitution barrier.

Parameter Comparison

Parameter	MQ 4.6 (Bel Fuse)	025104.6MXL (Littelfuse)	025104.6NRT1L (Littelfuse)
Current Rating (Amps)	4.6 A	4.6 A	4.6 A
Voltage Rating - AC	125 V	125 V	125 V
Voltage Rating - DC	125 V	125 V	125 V
Response Time	Fast Blow	Fast Blow	Fast Blow
Mounting Type	Through Hole	Through Hole	Through Hole
Fuse Type	Board Mount (Cartridge Style Excluded)	Board Mount (Cartridge Style Excluded)	Board Mount (Cartridge Style Excluded)
Package / Case	Axial	Axial	Axial
Breaking Capacity @ Rated Voltage	50 A AC, 300 A DC	50 A AC, 300 A DC	50 A AC, 300 A DC
Melting I²t	1.4	1.58	1.58
Operating Temperature	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C
Size / Dimension	0.125" Dia x 0.280" L (3.18mm x 7.10mm)	0.110" Dia x 0.280" L (2.80mm x 7.11mm)	0.110" Dia x 0.280" L (2.80mm x 7.11mm)
DC Cold Resistance	0.027 Ohms	0.024 Ohms	0.024 Ohms
Product Status	Obsolete	Active	Active
Approval Agency	CE, CSA, cURus	CSA, cURus, PSE, TUV	CSA, cURus, PSE, TUV

Engineering Selection Recommendations

Both Littelfuse PICO® II 251 series substitutes (025104.6MXL and 025104.6NRT1L) are active products with expanded regulatory approvals including PSE and TUV certification in addition to CSA and cURus. The MQ 4.6 carries CE, CSA, and cURus approvals.

Selection between the two Littelfuse alternatives depends on packaging requirements: 025104.6MXL is supplied in Bulk packaging, while 025104.6NRT1L is supplied in Cut Tape (CT) format. Both maintain electrical and mechanical equivalence to the obsolete MQ 4.6 across all critical parameters including current rating, voltage rating, response time, breaking capacity, and operating temperature range.

Frequently Asked Questions (FAQ)

Q: Can 025104.6MXL and 025104.6NRT1L be used interchangeably with MQ 4.6?

A: Yes. Both parts meet all electrical and mechanical equivalence criteria: 4.6 A current rating, 125 V AC/DC voltage rating, fast-blow response, 50 A AC / 300 A DC breaking capacity, and -55°C to 125°C operating temperature. The difference is packaging format (Bulk vs. Cut Tape), not functional performance.

Q: What is the significance of the dimension difference between MQ 4.6 and the Littelfuse substitutes?

A: The MQ 4.6 has a 0.125" diameter versus 0.110" for the Littelfuse parts. Both maintain the same 0.280" length. The diameter variance is within acceptable mechanical tolerance for through-hole axial fuse mounting and does not affect electrical performance or circuit board compatibility.

Q: Are there compliance differences between MQ 4.6 and the substitute parts?

A: The Littelfuse substitutes carry additional regulatory approvals (PSE, TUV) beyond the MQ 4.6 certifications (CE, CSA, cURus). Both maintain CSA and cURus approval, which are the primary North American certifications. The expanded approvals on Littelfuse parts provide broader market acceptance.

Q: Does the melting I²t difference (1.4 vs. 1.58) affect substitution?

A: The melting I²t values indicate thermal energy required to melt the fuse element. The 1.58 value for Littelfuse parts represents a minor variance within the fast-blow fuse category and does not prevent functional substitution for the 4.6 A circuit protection application.

Q: Which packaging format should be selected?

A: Selection between Bulk (025104.6MXL) and Cut Tape (025104.6NRT1L) depends on assembly process requirements. Cut Tape format is typically used for automated pick-and-place assembly, while Bulk packaging is used for manual assembly or reel-fed processes. Electrical performance is identical.

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