3AP 1.25-R Glass Fuse Cartridge Equivalent & Substitute Parts

Part Overview

The 3AP 1.25-R is a 1.25 A, 250 V AC/DC fast-blow glass fuse cartridge manufactured by Bel Fuse Inc. in the 3AB/3AG form factor (1/4" x 1-1/4" axial). This component is classified as obsolete, making equivalent substitute parts necessary for ongoing system maintenance and new design implementations. Substitute parts must maintain identical electrical ratings, mechanical dimensions, and mounting characteristics to ensure direct compatibility in existing circuit protection applications.

Key Parameters

Parameter	Specification
Current Rating	1.25 A
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Response Time	Fast Blow
Package / Case	3AB, 3AG, 1/4" x 1-1/4" (Axial)
Mounting Type	Through Hole
Operating Temperature Range	-55°C ~ 125°C
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitute parts for the 3AP 1.25-R are qualified based on the following mandatory parameters:

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

All substitute parts listed meet these criteria and are mechanically and electrically interchangeable with the original 3AP 1.25-R component.

Parameter Comparison

Parameter	3AP 1.25-R (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
Response Time	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow
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"
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	2.4	1.45	1.45	1.45	5.094
DC Cold Resistance (Ohms)	0.11	0.1385	0.1385	0.1385	0.122
Product Status	Obsolete	Active	Active	Active	Active
Approval Agency	CE, CSA, cULus	CE, CSA, KC, PSE, UL	CE, CSA, KC, PSE, UL	CE, CSA, KC, PSE, UL	CSA, UL
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	RoHS non-compliant

Engineering Selection Recommendations

All listed substitute parts meet the mandatory electrical and mechanical parameters for direct replacement of the 3AP 1.25-R. Selection among active alternatives should be based on the following criteria:

Littelfuse 318 Series (03181.25HXP, 03181.25MXP, 03181.25VXP): These parts are active products with ROHS3 compliance and comprehensive international certifications (CE, CSA, KC, PSE, UL). The 318 series variants are functionally equivalent and represent the primary recommended substitutes for new designs and ongoing maintenance.

Eaton AGC Series (BK/AGC-V-1-1/4): This part is an active product with CSA and UL certifications. However, it is RoHS non-compliant, which may restrict its use in applications requiring environmental compliance. The higher melting I²t value (5.094 vs. 2.4) indicates different thermal response characteristics compared to the original 3AP 1.25-R.

For applications requiring RoHS3 compliance and maximum certification coverage, the Littelfuse 318 series substitutes are preferred. For legacy systems without RoHS requirements, the Eaton AGC option remains viable.

Frequently Asked Questions (FAQ)

Q: Can the 03181.25HXP, 03181.25MXP, and 03181.25VXP be used interchangeably with the 3AP 1.25-R?

A: Yes. All three Littelfuse 318 series parts are electrically and mechanically equivalent to the 3AP 1.25-R. They share identical current ratings (1.25 A), voltage ratings (250 V AC), fuse type (cartridge glass), response time (fast blow), and package dimensions (3AB/3AG, 1/4" x 1-1/4" axial). Direct substitution is supported.

Q: What is the difference between the Littelfuse 318 variants (HXP, MXP, VXP)?

A: The provided data does not specify functional differences between these three variants. All three share identical electrical specifications, dimensions, and certifications. Consult Littelfuse technical documentation for variant-specific details.

Q: Why does the Eaton BK/AGC-V-1-1/4 have a different melting I²t value?

A: The melting I²t parameter (5.094 for Eaton vs. 2.4 for Bel Fuse) reflects differences in thermal response characteristics. Both parts meet the 1.25 A fast-blow specification, but the Eaton part exhibits different thermal behavior. Application-specific thermal analysis may be required to confirm compatibility in sensitive circuits.

Q: Is the Eaton BK/AGC-V-1-1/4 suitable for new designs?

A: The Eaton part is an active product with valid UL and CSA certifications. However, its RoHS non-compliant status may restrict use in applications subject to environmental regulations. For new designs, Littelfuse 318 series parts with ROHS3 compliance are recommended.

Q: Are all substitute parts available in the same packaging format?

A: The 3AP 1.25-R is specified with "-" packaging notation. Littelfuse 318 series parts are supplied in Bulk packaging. Eaton BK/AGC-V-1-1/4 is specified with "-" packaging notation. Verify packaging requirements with your procurement process.

Q: What certifications are required for my application?

A: The original 3AP 1.25-R carries CE, CSA, and cULus certifications. Littelfuse 318 series parts provide CE, CSA, KC, PSE, and UL certifications, offering broader international compliance. Eaton AGC parts provide CSA and UL certifications. Select based on your specific regulatory requirements.

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