Littelfuse 0318.125H Glass Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 0318.125H is a 125 mA, 250 V AC/DC fast-blow glass cartridge fuse 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 circuit protection applications. Active alternatives from the same manufacturer series maintain identical electrical and mechanical specifications while offering current product status and improved compliance certifications.

Key Parameters

Parameter	Value
Current Rating	125 mA
Voltage Rating (AC)	250 V
Response Time	Fast Blow
Package / Case	3AB, 3AG, 1/4" x 1-1/4" (Axial)
Fuse Type	Cartridge, Glass
Breaking Capacity @ Rated Voltage	35 A
Melting I²t	0.00289
Size / Dimension	0.275" Dia x 1.288" L (6.99mm x 32.72mm)
DC Cold Resistance	7.1 Ohms

Substitute Part Grouping Explanation

Substitution of the obsolete 0318.125H is based on strict equivalence across the following critical parameters:

Current Rating: 125 mA (exact match required)
Voltage Rating: 250 V AC (exact match required)
Response Time: Fast Blow (exact match required)
Package / Case: 3AB, 3AG, 1/4" x 1-1/4" (Axial) (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Breaking Capacity: 35 A (exact match required)
Melting I²t: 0.00289 (exact match required)

All substitute parts listed below meet these criteria and are manufactured by Littelfuse Inc. within the 318 series. The substitutes differ only in packaging configuration (bulk vs. tape) and compliance certifications, with no functional or electrical deviation.

Parameter Comparison

Part Number	Current Rating (mA)	Voltage Rating (V AC)	Response Time	Package / Case	Breaking Capacity (A)	Melting I²t	DC Cold Resistance (Ohms)	Product Status	RoHS Status
0318.125H	125	250	Fast Blow	3AB, 3AG, 1/4" x 1-1/4"	35	0.00289	7.1	Obsolete	RoHS Non-Compliant
0318.125HXP	125	250	Fast Blow	3AB, 3AG, 1/4" x 1-1/4"	35	0.00289	7.145	Active	ROHS3 Compliant
0318.125MXBP	125	250	Fast Blow	3AB, 3AG, 1/4" x 1-1/4"	35	0.00289	7.145	Active	ROHS3 Compliant
0318.125MXP	125	250	Fast Blow	3AB, 3AG, 1/4" x 1-1/4"	35	0.00289	7.145	Active	ROHS3 Compliant
0318.125VXP	125	250	Fast Blow	3AB, 3AG, 1/4" x 1-1/4"	35	0.00289	7.145	Active	ROHS3 Compliant

Engineering Selection Recommendations

The 0318.125H is obsolete and should be replaced with one of the four active substitute parts: 0318.125HXP, 0318.125MXBP, 0318.125MXP, or 0318.125VXP. All substitutes maintain identical electrical performance and mechanical compatibility.

Selection between the four active alternatives is determined by packaging and compliance requirements:

All four substitutes carry ROHS3 compliance, exceeding the non-compliant status of the original part
All four substitutes carry CE, CSA, and UL certifications, with the original part carrying only CSA and UL
All four substitutes operate across -55°C to 125°C, providing defined thermal performance versus the original part's unspecified operating temperature
Packaging differences (bulk vs. tape configurations) do not affect electrical or mechanical function

For new designs or component replenishment, any of the four active substitutes is functionally equivalent and represents an improvement in regulatory compliance and thermal specification clarity.

Frequently Asked Questions (FAQ)

Q: Can the 0318.125H be directly replaced with any of the listed substitutes?

A: Yes. All four substitute parts (0318.125HXP, 0318.125MXBP, 0318.125MXP, 0318.125VXP) are direct functional equivalents. They share identical current rating, voltage rating, response time, package dimensions, breaking capacity, and melting I²t characteristics. Physical installation is identical.

Q: What is the difference between the four substitute part numbers?

A: The four substitutes differ only in packaging configuration and suffix designation. All maintain identical electrical and mechanical specifications. Selection should be based on procurement packaging requirements (bulk vs. tape) and internal part numbering conventions.

Q: Are there any compliance differences between the original part and the substitutes?

A: Yes. The original 0318.125H is RoHS non-compliant, while all four substitutes are ROHS3 compliant. The substitutes also carry CE certification in addition to CSA and UL certifications present on the original part. The substitutes specify an operating temperature range of -55°C to 125°C, whereas the original part does not specify operating temperature limits.

Q: Is the DC cold resistance difference between the original part (7.1 Ohms) and substitutes (7.145 Ohms) significant?

A: No. The difference of 0.045 Ohms represents a 0.64% variance and is within normal manufacturing tolerance for glass cartridge fuses. This does not affect circuit protection performance or compatibility.

Q: Can substitutes be mixed in the same circuit or assembly?

A: Yes. All four substitutes are electrically and mechanically identical and can be used interchangeably within the same application or assembly.

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