3AP 4-R Glass Cartridge Fuse Equivalent & Substitute Parts

Part Overview

The 3AP 4-R is a 4 A, 250 V AC/DC glass cartridge fuse manufactured by Bel Fuse Inc. in the 3AB/3AG form factor with fast-blow response characteristics. This part is classified as obsolete, making equivalent substitutes necessary for ongoing system maintenance and new designs. The fuse is designed for through-hole mounting applications requiring reliable overcurrent protection in industrial and commercial equipment.

Key Parameters

Parameter	Value
Current Rating	4 A
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Package / Case	3AB, 3AG, 1/4" x 1/4" (Axial)
Response Time	Fast Blow
Breaking Capacity @ Rated Voltage	200 A
Mounting Type	Through Hole
Operating Temperature Range	-55°C ~ 125°C

Substitute Part Grouping Explanation

Substitution eligibility for the 3AP 4-R is determined by strict equivalence across the following parameters:

Current Rating: 4 A (exact match required)
Voltage Rating: 250 V AC (exact match required)
Package / Case: 3AB, 3AG form factor (exact match required)
Response Time: Fast Blow (exact match required)
Breaking Capacity: 200 A (exact match required)
Mounting Type: Through Hole (exact match required)

Parts are classified into two categories:

Direct Substitutes: Parts meeting all key parameters with identical electrical and mechanical specifications. These are interchangeable without design modification.

Similar Substitutes: Parts meeting all key parameters but with variations in secondary characteristics such as melting I²t, DC cold resistance, or compliance certifications. These require engineering evaluation for specific applications.

Parameter Comparison

Parameter	3AP 4-R (Bel Fuse)	0318004.HXP (Littelfuse)	0318004.MXP (Littelfuse)	0318004.VXP (Littelfuse)	BK/AGC-BV-4 (Eaton)	BK/AGC-V-4 (Eaton)
Manufacturer	Bel Fuse Inc.	Littelfuse Inc.	Littelfuse Inc.	Littelfuse Inc.	Eaton - Electronics Division	Eaton - Electronics Division
Current Rating (A)	4	4	4	4	4	4
Voltage Rating - AC (V)	250	250	250	250	250	250
Fuse Type	Cartridge, Glass	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"	3AB, 3AG, 1/4" x 1-1/4"
Response Time	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow	Fast Blow
Breaking Capacity @ Rated Voltage (A)	200	200	200	200	200	200
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Operating Temperature Range	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C
Melting I²t	36	28.5	28.5	28.5	86.56	86.56
DC Cold Resistance (Ohms)	0.026	0.0293	0.0293	0.0293	0.024	0.024
Size / Dimension (Dia x L)	0.272" x 1.280" (6.90mm x 32.50mm)	0.275" x 1.288" (6.99mm x 32.72mm)	0.275" x 1.288" (6.99mm x 32.72mm)	0.275" x 1.288" (6.99mm x 32.72mm)	0.266" x 1.292" (6.76mm x 32.82mm)	0.266" x 1.292" (6.76mm x 32.82mm)
Product Status	Obsolete	Active	Active	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	RoHS non-compliant	RoHS non-compliant
Approval Agency	CE, CSA, cULus, PSE	CE, CSA, KC, PSE, UL	CE, CSA, KC, PSE, UL	CE, CSA, KC, PSE, UL	CSA, UL	CSA, UL

Engineering Selection Recommendations

Direct Substitutes (Littelfuse 318 Series):

The Littelfuse 0318004.HXP, 0318004.MXP, and 0318004.VXP are direct substitutes for the 3AP 4-R. All three parts are active products with identical electrical ratings, package dimensions, and response characteristics. The Littelfuse parts carry expanded approval certifications (CE, CSA, KC, PSE, UL) compared to the original part, providing broader compliance coverage. All three are ROHS3 compliant. Dimensional variations are within manufacturing tolerance for the 3AB/3AG form factor. These parts are recommended as primary replacements.

Similar Substitutes (Eaton AGC Series):

The Eaton BK/AGC-BV-4 and BK/AGC-V-4 meet all core electrical and mechanical parameters but exhibit higher melting I²t values (86.56 versus 36 for the original part). This difference affects thermal response characteristics and may impact circuit protection timing in sensitive applications. Both Eaton parts are RoHS non-compliant and carry limited approval certifications (CSA, UL only). These parts are suitable for applications where RoHS compliance is not required and thermal response variation is acceptable.

Frequently Asked Questions (FAQ)

Q: Can the Littelfuse 318 series parts be used interchangeably with the 3AP 4-R?

A: Yes. The 0318004.HXP, 0318004.MXP, and 0318004.VXP are direct substitutes meeting identical electrical ratings, package specifications, and response characteristics. All are active products with current manufacturing support.

Q: What is the difference between the three Littelfuse substitute parts?

A: The 0318004.HXP, 0318004.MXP, and 0318004.VXP are electrically and mechanically identical. Differences are limited to packaging and internal manufacturing variants. Selection among these three is based on availability and packaging preference.

Q: Why do the Eaton AGC parts have higher melting I²t values?

A: Melting I²t is a thermal characteristic that determines the energy required to melt the fuse element. The Eaton parts (86.56) have higher values than the original 3AP 4-R (36), resulting in slower thermal response. This affects the time-current characteristic curve and may alter circuit protection behavior in applications with specific thermal requirements.

Q: Are the Eaton AGC parts suitable replacements?

A: The Eaton parts meet all core electrical and mechanical parameters but differ in thermal response and compliance certifications. They are suitable for applications where RoHS compliance is not required and thermal response variation is acceptable. Applications requiring exact thermal matching should use the Littelfuse 318 series.

Q: What are the dimensional tolerances for the 3AB/3AG form factor?

A: All substitute parts maintain the 3AB/3AG form factor with minor dimensional variations within manufacturing tolerance. The original part measures 0.272" Dia x 1.280" L; substitute parts range from 0.266" to 0.275" Dia and 1.288" to 1.292" L. These variations do not affect mechanical fit in standard 3AB/3AG fuse holders.

Q: Which substitute part offers the best compliance coverage?

A: The Littelfuse 318 series (0318004.HXP, 0318004.MXP, 0318004.VXP) provides the broadest approval certifications (CE, CSA, KC, PSE, UL) and ROHS3 compliance, making them suitable for applications with stringent regulatory requirements.

Q: Can I mix substitute parts from different manufacturers in the same circuit?

A: While all substitute parts meet the same electrical ratings and package specifications, mixing parts with different thermal characteristics (melting I²t) in the same circuit is not recommended. Consistent thermal response across all fuses in a circuit ensures predictable protection behavior.

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