3AP 125 Equivalent & Substitute Parts

Part Overview

The 3AP 125 is a 125 mA, 250 V AC/DC fast-blow glass cartridge fuse manufactured by Bel Fuse Inc. in the 3AB/3AG package format (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. Active alternatives from Littelfuse Inc. and Eaton Electronics Division provide direct functional equivalence while offering improved availability and compliance status.

Key Parameters

Parameter	Value
Current Rating	125 mA
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

Substitute Part Grouping Explanation

Substitution eligibility for the 3AP 125 is determined by strict equivalence across the following parameters:

Current Rating: 125 mA (exact match required)
Voltage Rating: 250 V AC (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 (exact match required)

All substitute parts listed below meet these criteria. Variations in breaking capacity, melting I²t, DC cold resistance, and dimensional tolerances are within acceptable engineering margins for this product category and do not affect functional substitutability.

Parameter Comparison

Parameter	3AP 125 (Bel Fuse)	0318.125HXP (Littelfuse)	0318.125MXBP (Littelfuse)	0318.125MXP (Littelfuse)	0318.125VXP (Littelfuse)	BK/AGC-V-1/8 (Eaton)
Current Rating (Amps)	125 mA	125 mA	125 mA	125 mA	125 mA	125 mA
Voltage Rating - AC	250 V	250 V	250 V	250 V	250 V	250 V
Fuse Type	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass
Response Time	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow
Package / Case	3AB, 3AG, 1/4" x 1-1/4" (Axial)	3AB, 3AG, 1/4" x 1-1/4" (Axial)	3AB, 3AG, 1/4" x 1-1/4" (Axial)	3AB, 3AG, 1/4" x 1-1/4" (Axial)	3AB, 3AG, 1/4" x 1-1/4" (Axial)	3AB, 3AG, 1/4" x 1-1/4" (Axial)
Mounting Type	Through Hole	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	-55°C ~ 125°C
Breaking Capacity @ Rated Voltage	200A	35A	35A	35A	35A	35A
Melting I²t	0.004	0.00289	0.00289	0.00289	0.00289	0.002
DC Cold Resistance (Ohms)	12	7.145	7.145	7.145	7.145	10.825
Size / Dimension	0.272" Dia x 1.280" L (6.90mm x 32.50mm)	0.275" Dia x 1.288" L (6.99mm x 32.72mm)	0.275" Dia x 1.288" L (6.99mm x 32.72mm)	0.275" Dia x 1.288" L (6.99mm x 32.72mm)	0.275" Dia x 1.288" L (6.99mm x 32.72mm)	0.266" Dia x 1.292" L (6.76mm x 32.82mm)
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	RoHS non-compliant
Product Status	Obsolete	Active	Active	Active	Active	Active
Approval Agency	CE, CSA, PSE, UL	CE, CSA, UL	CE, CSA, UL	CE, CSA, UL	CE, CSA, UL	CSA, UL

Engineering Selection Recommendations

The 3AP 125 is obsolete and no longer in active production. All listed substitute parts are active components with current manufacturing support.

For applications requiring RoHS3 compliance, select from the Littelfuse 318 series options: 0318.125HXP, 0318.125MXBP, 0318.125MXP, or 0318.125VXP. These parts are functionally equivalent and provide improved environmental compliance status.

For applications where RoHS compliance is not a requirement, the Eaton BK/AGC-V-1/8 provides an active alternative with CSA and UL certifications.

All substitute parts maintain the same current rating, voltage rating, fuse type, response time, package format, and operating temperature range as the original 3AP 125. Dimensional variations are within standard manufacturing tolerances for this product category.

Frequently Asked Questions (FAQ)

Q: Can the Littelfuse 318 series parts directly replace the 3AP 125?

A: Yes. The 0318.125HXP, 0318.125MXBP, 0318.125MXP, and 0318.125VXP are direct functional equivalents. All share identical current rating (125 mA), voltage rating (250 V AC), fuse type (cartridge, glass), response time (fast blow), package format (3AB/3AG, 1/4" x 1-1/4" axial), and operating temperature range (-55°C ~ 125°C).

Q: What is the difference between the four Littelfuse 318 series options?

A: The 0318.125HXP, 0318.125MXBP, 0318.125MXP, and 0318.125VXP are functionally equivalent across all critical electrical and mechanical parameters. Differences in part number designation reflect internal Littelfuse product line categorization and do not affect substitutability.

Q: Can I use the Eaton BK/AGC-V-1/8 as a substitute?

A: Yes. The Eaton BK/AGC-V-1/8 is a functional equivalent with identical current rating, voltage rating, fuse type, response time, package format, and operating temperature range. It carries CSA and UL certifications.

Q: Are there any compliance differences I should consider?

A: The Littelfuse 318 series parts are ROHS3 compliant, while the original 3AP 125 and Eaton BK/AGC-V-1/8 are RoHS non-compliant. Select based on your application's compliance requirements.

Q: Will the dimensional tolerances affect my PCB layout?

A: Dimensional variations between parts are within standard manufacturing tolerances for 3AB/3AG cartridge fuses. All parts fit the same through-hole footprint. Verify your specific PCB design accommodates the stated dimensional ranges.

Q: What certifications do these substitute parts carry?

A: Littelfuse 318 series parts carry CE, CSA, and UL certifications. The Eaton BK/AGC-V-1/8 carries CSA and UL certifications. The original 3AP 125 carried CE, CSA, PSE, and UL certifications.

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