Littelfuse 03121.25MXP Glass Cartridge Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 03121.25MXP is a 1.25 A, 250 V AC/DC fast-blow glass cartridge fuse in the 3AB/3AG package format (1/4" x 1-1/4"). This component is classified as Active product status and is designed for applications requiring reliable overcurrent protection in holder-based installations. Substitute parts are necessary when the primary manufacturer part becomes unavailable, when inventory constraints exist, or when design flexibility across approved suppliers is required while maintaining identical electrical and mechanical specifications.

Substiute Parts

03121.25MXP

Littelfuse Inc.In Stock: 139503121.25MXP Datasheet

Current PartRFQ

0001.1025

SCHURTER Inc.In Stock: 12820001.1025 Datasheet

MFR RecommendedRFQ

3AG 1.25-R

Bel Fuse Inc.In Stock: 14713AG 1.25-R Datasheet

MFR RecommendedRFQ

BK/AGC-1-1/4-R

Eaton - Electronics DivisionIn Stock: 1991BK/AGC-1-1/4-R Datasheet

Parametric EquivalentRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the 03121.25MXP is determined by strict equivalence across the following parameters:

• Current Rating: 1.25 A (exact match required)
• Voltage Rating (AC): 250 V (exact match required)
• Response Time: Fast Blow (exact match required)
• Fuse Type: Cartridge, Glass (exact match required)
• Package / Case: 3AB, 3AG, 1/4" x 1-1/4" (exact match required)
• Mounting Type: Requires Holder (exact match required)

All substitute parts listed below meet these criteria. Variations in breaking capacity, melting I²t, DC cold resistance, and operating temperature ranges are permitted within the scope of this product category, as these parameters do not affect mechanical or electrical interchangeability in standard holder-based installations.

Parameter Comparison

Engineering Selection Recommendations

Primary Selection (Active Status with Full Compliance):

• 3AG 1.25-R (Bel Fuse Inc.): Active product status with CE, CSA, cULus, and PSE certifications. Operating temperature range of -55°C ~ 125°C matches the main part. Breaking capacity of 200 A exceeds the main part specification.
• BK/AGC-1-1/4-R (Eaton - Electronics Division): Active product status with CSA and UL certifications. Operating temperature range of -55°C ~ 125°C matches the main part. Breaking capacity of 100 A matches the main part specification.

Secondary Selection (Obsolete Status):

• 0001.1025 (SCHURTER Inc.): Marked as Obsolete product status. Operating temperature range is restricted to -40°C ~ 85°C, which is narrower than the main part. No approval agency certifications are listed. This part should be selected only when primary alternatives are unavailable and application temperature requirements fall within the -40°C ~ 85°C range.

Frequently Asked Questions (FAQ)

Q: Can I use 0001.1025 (SCHURTER) as a direct replacement for 03121.25MXP? A: The 0001.1025 meets the core electrical and mechanical parameters (1.25 A, 250 V, fast-blow, 3AB/3AG package). However, it is classified as Obsolete and has a restricted operating temperature range (-40°C ~ 85°C versus -55°C ~ 125°C). Use only if application conditions remain within the narrower temperature range and inventory availability is critical.

Q: What is the difference between the breaking capacity values listed for each part? A: Breaking capacity indicates the maximum current the fuse can safely interrupt at rated voltage. All listed parts are rated for 1.25 A operation. The variations in breaking capacity (100 A, 200 A, 1.5 kA) do not affect interchangeability in standard applications but reflect different design margins and manufacturing standards across suppliers.

Q: Are all substitute parts RoHS3 compliant? A: Yes. All parts listed—03121.25MXP, 0001.1025, 3AG 1.25-R, and BK/AGC-1-1/4-R—are ROHS3 Compliant and REACH Unaffected.

Q: Which substitute part has the broadest regulatory approval? A: The 03121.25MXP (main part) carries the most comprehensive approvals: CE, CSA, KC, PSE, and UL. The 3AG 1.25-R (Bel Fuse) follows with CE, CSA, cULus, and PSE. The BK/AGC-1-1/4-R (Eaton) carries CSA and UL. The 0001.1025 (SCHURTER) lists no approval agencies.

Q: Can I substitute these parts in applications requiring operation below -40°C? A: Only the 03121.25MXP, 3AG 1.25-R, and BK/AGC-1-1/4-R are rated for operation down to -55°C. The 0001.1025 is limited to -40°C minimum. For applications requiring -55°C operation, use only the three parts with extended low-temperature ratings.

Q: Are the physical dimensions identical across all substitute parts? A: Dimensions are nominally equivalent. The main part and Eaton BK/AGC-1-1/4-R are specified as 0.250" Dia x 1.250" L (6.35mm x 31.75mm). The SCHURTER 0001.1025 and Bel Fuse 3AG 1.25-R are specified as 0.250" Dia x 1.252" L (6.35mm x 31.80mm). This 0.002" (0.05mm) difference in length is within standard manufacturing tolerance and does not affect holder compatibility.