5MT 3 Glass Cartridge Fuse - Equivalent & Substitute Parts

Part Overview

The 5MT 3 is a 3A 250VAC glass cartridge fuse manufactured by Bel Fuse Inc., designed for 5mm x 20mm holder applications. This component is classified as obsolete, making equivalent substitute parts necessary for ongoing system maintenance and new designs. The fuse provides medium-blow response characteristics with a breaking capacity of 100A at rated voltage and operates across a temperature range of -55°C to 125°C.

Key Parameters

Parameter	Value
Current Rating	3 A
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Package / Case	5mm x 20mm
Response Time	Medium Blow
Breaking Capacity @ Rated Voltage	100A
Operating Temperature Range	-55°C ~ 125°C
Mounting Type	Requires Holder
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution for the 5MT 3 is determined by strict equivalence across the following electrical and mechanical parameters:

Current Rating: 3 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)
Breaking Capacity: 100A (exact match required)
Operating Temperature Range: -55°C ~ 125°C (exact match required)

The substitute parts listed below meet all these criteria. Response time characteristics (Medium Blow vs. Slow Blow) and melting I²t values differ among substitutes and must be evaluated based on circuit protection requirements. All substitutes are active products from established manufacturers with current availability.

Parameter Comparison

Parameter	5MT 3 (Bel Fuse)	0232003.MXP (Littelfuse)	0239003.HXP (Littelfuse)	BK1/GMD-3-R (Eaton)
Current Rating (Amps)	3 A	3 A	3 A	3 A
Voltage Rating - AC	250 V	250 V	250 V	250 V
Fuse Type	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass
Package / Case	5mm x 20mm	5mm x 20mm	5mm x 20mm	5mm x 20mm
Response Time	Medium Blow	Medium Blow	Slow Blow	Slow Blow
Breaking Capacity @ Rated Voltage	100A	100A	100A	100A
Melting I²t	58	17.19	129.51	145
DC Cold Resistance (Ohms)	0.035	0.0226	0.04877	0.0655
Operating Temperature	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C
Product Status	Obsolete	Active	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Approval Agency	CE, CSA, cULus, PSE	CE, KC, PSE	CE, CSA, KC, PSE, UL	CSA, PSE/JET, UL

Engineering Selection Recommendations

All three substitute parts are active products with current manufacturing status, addressing the obsolescence of the 5MT 3.

The 0232003.MXP (Littelfuse 232 series) maintains the medium-blow response characteristic of the original 5MT 3, making it the closest functional equivalent. This part carries ROHS3 compliance and CE, KC, and PSE certifications. The melting I²t value of 17.19 is significantly lower than the original, which may affect circuit protection timing in sensitive applications.

The 0239003.HXP (Littelfuse 239 series) provides slow-blow response with the broadest certification coverage (CE, CSA, KC, PSE, UL). The melting I²t of 129.51 is substantially higher than the original, providing extended protection against transient overcurrents. This part is suitable for applications requiring delayed response characteristics.

The BK1/GMD-3-R (Eaton GMD series) also provides slow-blow response with the highest melting I²t value (145) and carries CSA, PSE/JET, and UL certifications. DC cold resistance is highest among the substitutes at 0.0655 Ohms.

Selection should be based on circuit protection requirements, response time characteristics needed for the application, and required regulatory certifications.

Frequently Asked Questions (FAQ)

Q: Can the 0232003.MXP be used as a direct replacement for the 5MT 3?

A: The 0232003.MXP meets all electrical and mechanical equivalence criteria: 3A current rating, 250V AC voltage rating, 5mm x 20mm package, 100A breaking capacity, and identical operating temperature range. Both parts feature medium-blow response. Physical dimensions differ slightly (5.20mm vs. 5.10mm diameter), but both fit standard 5mm x 20mm holders. Compatibility depends on holder specifications and circuit protection timing requirements.

Q: What is the difference between medium-blow and slow-blow fuses?

A: Response time classification indicates the fuse element's thermal response to overcurrent. Medium-blow fuses (5MT 3, 0232003.MXP) operate with standard thermal characteristics. Slow-blow fuses (0239003.HXP, BK1/GMD-3-R) tolerate temporary overcurrent surges before melting, providing extended protection. Selection depends on circuit load characteristics and transient current behavior.

Q: Are all substitutes RoHS compliant?

A: The 5MT 3 is RoHS non-compliant. All three substitute parts (0232003.MXP, 0239003.HXP, BK1/GMD-3-R) are ROHS3 compliant, meeting current environmental regulations.

Q: Which substitute has the broadest regulatory certification?

A: The 0239003.HXP carries five regulatory certifications (CE, CSA, KC, PSE, UL), providing the widest acceptance across global markets and applications.

Q: How do melting I²t values affect fuse selection?

A: Melting I²t represents the thermal energy required to melt the fuse element. Lower values (0232003.MXP at 17.19) provide faster response to sustained overcurrent. Higher values (BK1/GMD-3-R at 145) allow greater energy absorption before melting. Circuit design and load characteristics determine the appropriate I²t value for protection.

Q: Can substitutes be used interchangeably in existing 5MT 3 applications?

A: All substitutes fit the 5mm x 20mm holder and match the 3A/250V electrical ratings. However, differences in response time and melting I²t may alter circuit protection behavior. Application-specific evaluation is required to confirm suitability.

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