3AP 1.25 Glass Fuse Cartridge Equivalent & Substitute Parts

Part Overview

The Bel Fuse Inc. 3AP 1.25 is a 1.25 A, 250 V AC/DC fast-blow glass fuse cartridge in 3AB/3AG package format with axial through-hole mounting. This component is classified as obsolete, making identification of functionally equivalent substitute parts essential for ongoing system maintenance and new design implementations. Equivalent alternatives from active manufacturers ensure continued availability and compliance with current regulatory standards.

Key Parameters

Parameter	Value
Current Rating	1.25 A
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Package / Case	3AB, 3AG, 1/4" x 1-1/4" (Axial)
Response Time	Fast Blow
Mounting Type	Through Hole
Operating Temperature Range	-55°C ~ 125°C

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following parameters:

Current Rating: 1.25 A (exact match required)
Voltage Rating: 250 V AC (exact match required)
Package / Case: 3AB, 3AG, 1/4" x 1-1/4" (Axial) (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Response Time: Fast Blow (exact match required)
Mounting Type: Through Hole (exact match required)

All substitute parts listed meet these core electrical and mechanical parameters. Variations in secondary parameters such as breaking capacity, melting I²t, DC cold resistance, and approval agencies do not preclude substitution but may influence selection based on specific application requirements.

Parameter Comparison

Parameter	3AP 1.25 (Bel Fuse)	03181.25HXP (Littelfuse)	03181.25MXP (Littelfuse)	03181.25VXP (Littelfuse)	BK/AGC-V-1-1/4 (Eaton)
Current Rating (Amps)	1.25 A	1.25 A	1.25 A	1.25 A	1.25 A
Voltage Rating - AC	250 V	250 V	250 V	250 V	250 V
Fuse Type	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass
Package / Case	3AB, 3AG, 1/4" x 1-1/4"	3AB, 3AG, 1/4" x 1-1/4"	3AB, 3AG, 1/4" x 1-1/4"	3AB, 3AG, 1/4" x 1-1/4"	3AB, 3AG, 1/4" x 1-1/4"
Response Time	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Operating Temperature	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C
Breaking Capacity @ Rated Voltage	200 A	100 A	100 A	100 A	100 A
Melting I²t	2.45	1.45	1.45	1.45	5.094
DC Cold Resistance (Ohms)	0.114	0.1385	0.1385	0.1385	0.122
Product Status	Obsolete	Active	Active	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	RoHS non-compliant
Approval Agency	CE, CSA, PSE, UL	CE, CSA, KC, PSE, UL	CE, CSA, KC, PSE, UL	CE, CSA, KC, PSE, UL	CSA, UL

Engineering Selection Recommendations

Littelfuse 03181.25HXP, 03181.25MXP, 03181.25VXP Series: These three Littelfuse variants are functionally equivalent substitutes with identical electrical and mechanical specifications. All three are active products with ROHS3 compliance and comprehensive approval agency certifications (CE, CSA, KC, PSE, UL). Selection among these three variants may be based on packaging availability and inventory status. The Littelfuse series exhibits lower melting I²t (1.45 vs. 2.45) and slightly higher DC cold resistance compared to the original 3AP 1.25.

Eaton BK/AGC-V-1-1/4: This Eaton AGC series fuse meets all core electrical and mechanical substitution criteria. It maintains active product status and carries CSA and UL certifications. The Eaton variant exhibits higher melting I²t (5.094) and lower DC cold resistance (0.122 Ohms) relative to the original part. RoHS non-compliance status aligns with the original 3AP 1.25. Selection of this variant is appropriate where Eaton component standardization is required or where the higher melting I²t characteristic is beneficial to the application.

For new designs or systems requiring regulatory compliance with current standards, Littelfuse variants are preferred due to ROHS3 compliance and broader certification coverage.

Frequently Asked Questions (FAQ)

Q: Can the Littelfuse 03181.25HXP, 03181.25MXP, and 03181.25VXP be used interchangeably? A: Yes. All three Littelfuse variants are electrically and mechanically identical. They differ only in packaging and internal manufacturing specifications that do not affect circuit performance. Selection is based on availability and procurement requirements.

Q: What is the significance of the different melting I²t values? A: Melting I²t defines the thermal energy required to melt the fuse element. The original 3AP 1.25 has a melting I²t of 2.45, while Littelfuse substitutes have 1.45 and Eaton has 5.094. These differences affect the fuse's response to transient overcurrent conditions. For applications sensitive to transient behavior, verify that the substitute's melting I²t is acceptable for your circuit protection requirements.

Q: Are there RoHS compliance considerations for substitute selection? A: The original 3AP 1.25 is RoHS non-compliant. Littelfuse substitutes (03181.25HXP, 03181.25MXP, 03181.25VXP) are ROHS3 compliant, making them suitable for new designs subject to RoHS regulations. The Eaton BK/AGC-V-1-1/4 maintains RoHS non-compliance status.

Q: Do all substitutes fit the same physical footprint? A: Yes. All substitute parts use the identical 3AB, 3AG, 1/4" x 1-1/4" (Axial) package format with through-hole mounting. Physical dimensions are equivalent within manufacturing tolerances (original: 0.272" Dia x 1.280" L; substitutes: 0.275" Dia x 1.288" L; Eaton: 0.266" Dia x 1.292" L).

Q: Which substitute offers the broadest approval agency coverage? A: Littelfuse variants (03181.25HXP, 03181.25MXP, 03181.25VXP) carry certifications from CE, CSA, KC, PSE, and UL. The original 3AP 1.25 includes PSE certification, which is not present in the Eaton variant. For applications requiring PSE compliance, Littelfuse substitutes are the appropriate choice.

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