Equivalent & Substitute Parts for 5MT 1.25 Glass Cartridge Fuse

Part Overview

The Bel Fuse Inc. 5MT 1.25 is a 1.25 A, 250 V AC/DC glass cartridge fuse in 5mm x 20mm form factor with medium blow response time. This part is classified as obsolete, making equivalent substitutes necessary for ongoing system maintenance and new designs. The fuse requires a holder for installation and is rated for 100 A breaking capacity at rated voltage. Substitute parts must maintain electrical compatibility while meeting current availability and compliance requirements.

Key Parameters

Parameter	Value
Current Rating	1.25 A
Voltage Rating (AC)	250 V
Package / Case	5mm x 20mm
Fuse Type	Cartridge, Glass
Mounting Type	Requires Holder
Response Time	Medium Blow
Breaking Capacity @ Rated Voltage	100 A
Operating Temperature Range	-55°C ~ 125°C

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict adherence to the following electrical and mechanical parameters:

Primary Compatibility Criteria:

Current Rating: 1.25 A (exact match required)
Voltage Rating: 250 V AC (exact match required)
Package / Case: 5mm x 20mm (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Mounting Type: Requires Holder (exact match required)

Secondary Consideration Parameters:

Response Time: Medium Blow or Slow Blow acceptable for general substitution
Breaking Capacity: 35 A, 80 A, or 100 A acceptable depending on circuit requirements
Operating Temperature: -55°C ~ 125°C preferred; -25°C ~ 70°C acceptable for limited temperature applications
Approval Agencies: CE, CSA, cULus, PSE, and additional certifications enhance compliance flexibility

All substitute parts listed meet the primary compatibility criteria. Differences in response time, breaking capacity, and thermal characteristics are documented to enable informed selection based on specific circuit requirements.

Parameter Comparison

Part Number	Manufacturer	Current (A)	Voltage (V AC)	Package	Response Time	Breaking Capacity (A)	Melting I²t	Operating Temp (°C)	Product Status	RoHS Status
5MT 1.25	Bel Fuse Inc.	1.25	250	5x20mm	Medium Blow	100	7.2	-55 ~ 125	Obsolete	Non-compliant
02131.25MXP	Littelfuse Inc.	1.25	250	5x20mm	Slow Blow	35	27.15	-55 ~ 125	Active	ROHS3 Compliant
02181.25TXP	Littelfuse Inc.	1.25	250	5x20mm	Slow Blow	35	12.65	-55 ~ 125	Active	ROHS3 Compliant
02321.25MXP	Littelfuse	1.25	250	5x20mm	Medium Blow	100	4.11	-55 ~ 125	Active	ROHS3 Compliant
02391.25HXP	Littelfuse Inc.	1.25	250	5x20mm	Slow Blow	100	19.525	-55 ~ 125	Active	ROHS3 Compliant
20111250021	Littelfuse Inc.	1.25	250	5x20mm	Medium Blow	80	3.2	-25 ~ 70	Active	ROHS3 Compliant
BK1/GMD-1.25-R	Eaton - Electronics Division	1.25	250	5x20mm	Slow Blow	100	16	Not specified	Active	ROHS3 Compliant
GDC-1.25A	Eaton - Electronics Division	1.25	250	5x20mm	Slow Blow	35	10.05	Not specified	Active	Not specified

Engineering Selection Recommendations

Direct Replacement (Matching Response Time and Breaking Capacity):

02321.25MXP: Active status, ROHS3 compliant, medium blow response, 100 A breaking capacity. Closest electrical match to the 5MT 1.25 with modern compliance certifications.

Alternative Substitutes (Different Response Time):

02181.25TXP: Active status, ROHS3 compliant, slow blow response, 35 A breaking capacity. Suitable for circuits tolerating slower response characteristics.
02391.25HXP: Active status, ROHS3 compliant, slow blow response, 100 A breaking capacity. Appropriate for applications requiring extended thermal response.
BK1/GMD-1.25-R: Active status, ROHS3 compliant, slow blow response, 100 A breaking capacity. Eaton alternative with equivalent breaking capacity.

Limited Temperature Range:

20111250021: Active status, ROHS3 compliant, medium blow response, 80 A breaking capacity. Operating temperature restricted to -25°C ~ 70°C; suitable only for applications within this range.

Lower Breaking Capacity:

02131.25MXP: Active status, ROHS3 compliant, slow blow response, 35 A breaking capacity. Acceptable for circuits with lower fault current requirements.
GDC-1.25A: Active status, slow blow response, 35 A breaking capacity. Eaton alternative with lower breaking capacity.

All substitute parts are currently in active production status with modern compliance certifications, ensuring long-term availability and regulatory compliance.

Frequently Asked Questions (FAQ)

Q: Can I use a substitute fuse with a different response time (slow blow instead of medium blow)? A: Yes. Slow blow fuses provide extended thermal response compared to medium blow. Selection depends on circuit tolerance for delayed response. Verify circuit design specifications before substitution.

Q: What is the significance of breaking capacity differences (35 A, 80 A, 100 A)? A: Breaking capacity indicates the maximum fault current the fuse can safely interrupt. The 5MT 1.25 is rated 100 A. Substitutes with lower breaking capacity (35 A, 80 A) are acceptable only if circuit fault current does not exceed the substitute's rating.

Q: Are all substitute parts compatible with existing fuse holders? A: Yes. All substitute parts maintain the 5mm x 20mm package dimension and cartridge glass form factor, ensuring mechanical compatibility with standard 5x20mm fuse holders.

Q: Why is the 5MT 1.25 classified as obsolete? A: Bel Fuse Inc. has discontinued this product line. Active alternatives from Littelfuse and Eaton provide equivalent electrical performance with current manufacturing support and modern compliance certifications.

Q: Which substitute offers the closest electrical match? A: The 02321.25MXP provides the closest match, maintaining medium blow response time and 100 A breaking capacity identical to the 5MT 1.25, with ROHS3 compliance and active production status.

Q: Can I use the 20111250021 in all applications? A: The 20111250021 has a restricted operating temperature range of -25°C ~ 70°C compared to the 5MT 1.25 range of -55°C ~ 125°C. Use only in applications operating within this narrower temperature window.

Q: What compliance certifications should I verify for my application? A: Verify that the selected substitute meets your system's required approval agencies. Common certifications include CE, CSA, cULus, PSE, UL, and VDE. Consult your system documentation for specific requirements.

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