Littelfuse 03121.75H Glass Cartridge Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 03121.75H is a 1.75 A, 250 V AC/DC fast-blow glass cartridge fuse in the 312 series, designed for 3AB and 3AG holder applications with dimensions of 0.250" diameter × 1.250" length. The part is currently obsolete, necessitating identification of active equivalent alternatives that maintain identical electrical and mechanical specifications for direct replacement in existing applications.

Substiute Parts

03121.75H

Littelfuse Inc.In Stock: 124003121.75H Datasheet

Current PartRFQ

03121.75HXP

Littelfuse Inc.In Stock: 104103121.75HXP Datasheet

DirectRFQ

03121.75MXP

Littelfuse Inc.In Stock: 105903121.75MXP Datasheet

Parametric EquivalentRFQ

03121.75VXP

Littelfuse Inc.In Stock: 89503121.75VXP Datasheet

Parametric EquivalentRFQ

AGC-1-3/4-R

Eaton - Electronics DivisionIn Stock: 965AGC-1-3/4-R Datasheet

Parametric EquivalentRFQ

BK/AGC-1-3/4-R

Eaton - Electronics DivisionIn Stock: 1094BK/AGC-1-3/4-R Datasheet

Parametric EquivalentRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following parameters: current rating (1.75 A), voltage rating (250 V AC), fuse type (cartridge glass), response time (fast blow), package designation (3AB, 3AG), and physical dimensions (0.250" × 1.250"). All identified substitutes maintain these specifications without deviation.

The substitute parts are grouped into two categories:

Littelfuse 312 Series (Direct Manufacturer Equivalents): 03121.75HXP, 03121.75MXP, and 03121.75VXP are active production variants within the same manufacturer series, differing only in packaging configuration and compliance certifications.

Eaton AGC Series (Cross-Manufacturer Parametric Equivalents): AGC-1-3/4-R and BK/AGC-1-3/4-R are produced by Eaton - Electronics Division and provide identical electrical and mechanical performance within the AGC series designation.

Parameter Comparison

Engineering Selection Recommendations

For applications currently using the obsolete 03121.75H, the Littelfuse 312 series variants (03121.75HXP, 03121.75MXP, 03121.75VXP) are the primary substitutes. All three maintain active production status and provide expanded regulatory certifications including CE, CSA, PSE, and UL approval, with full ROHS3 compliance and REACH unaffected status.

The Eaton AGC series alternatives (AGC-1-3/4-R and BK/AGC-1-3/4-R) provide cross-manufacturer parametric equivalence with identical electrical and mechanical specifications. BK/AGC-1-3/4-R offers ROHS3 compliance and REACH unaffected status, while AGC-1-3/4-R provides RoHS compliance. Both are in active production.

Selection between Littelfuse and Eaton variants depends on existing supply chain relationships and regulatory compliance requirements specific to the end application. All substitutes are mechanically and electrically interchangeable within 3AB and 3AG holder applications.

Frequently Asked Questions (FAQ)

Q: Can the 03121.75H be directly replaced with any of the listed substitutes?

A: Yes. All listed substitutes maintain identical current rating (1.75 A), voltage rating (250 V AC), fuse type (cartridge glass), response time (fast blow), package designation (3AB, 3AG), and physical dimensions (0.250" × 1.250"). Direct mechanical and electrical interchangeability is confirmed.

Q: What is the difference between the Littelfuse 312 series variants?

A: The 03121.75HXP, 03121.75MXP, and 03121.75VXP differ in packaging configuration and internal manufacturing processes, but all maintain identical electrical specifications, melting I²t (3.6), and operating temperature range (-55°C ~ 125°C). All three are active production parts with expanded regulatory certifications.

Q: Are the Eaton AGC series fuses compatible with existing 3AB and 3AG holders?

A: Yes. The AGC-1-3/4-R and BK/AGC-1-3/4-R maintain the same package designation (3AB, 3AG) and physical dimensions (0.250" × 1.250") as the original 03121.75H, ensuring mechanical compatibility with existing holder applications.

Q: What compliance certifications should I consider for new designs?

A: The Littelfuse 312 series variants (03121.75HXP, 03121.75MXP, 03121.75VXP) provide the broadest regulatory coverage with CE, CSA, PSE, and UL approvals, plus ROHS3 compliance. The Eaton BK/AGC-1-3/4-R offers ROHS3 compliance and REACH unaffected status. Selection depends on target market and regulatory requirements.

Q: Is there a difference in breaking capacity between substitutes?

A: The Littelfuse 312 series variants specify 100 A breaking capacity at rated voltage, compared to 35 A for the original 03121.75H. The Eaton AGC series does not specify breaking capacity. For applications where breaking capacity is a critical parameter, the Littelfuse variants provide enhanced performance.

Q: Can I mix different substitute parts in the same application?

A: Yes. All substitutes maintain identical electrical and mechanical specifications for the 1.75 A, 250 V AC fast-blow cartridge fuse function. However, maintaining consistency within a single design or system is recommended for supply chain and documentation purposes.