Equivalent & Substitute Parts for 5MT 3-R Glass Cartridge Fuse

Part Overview

The 5MT 3-R is a 3A 250VAC glass cartridge fuse manufactured by Bel Fuse Inc., designed for 5mm x 20mm holder applications. This part is classified as obsolete, making equivalent substitutes necessary for ongoing system maintenance and new designs. The fuse provides medium-blow response characteristics suitable for general-purpose circuit protection in AC/DC applications operating across -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	100A @ Rated Voltage
Operating Temperature Range	-55°C ~ 125°C
Mounting Type	Requires Holder
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict alignment with the following core parameters: current rating (3A), voltage rating (250VAC), fuse type (cartridge glass), physical package (5mm x 20mm), breaking capacity (100A), and operating temperature range (-55°C to 125°C). All identified substitutes meet these mandatory criteria.

Substitutes are grouped into two categories based on response time characteristics:

Medium-Blow Response (Direct Functional Equivalents):

0234003.MXP (Littelfuse 234 Series)
0232003.MXP (Littelfuse 232 Series)

Slow-Blow Response (Functional Alternatives):

0239003.HXP (Littelfuse 239 Series)
BK1/GMD-3-R (Eaton GMD Series)

The response time difference reflects thermal characteristics that affect trip behavior under transient conditions. Medium-blow fuses respond faster to overcurrent, while slow-blow fuses tolerate brief inrush currents before activation.

Parameter Comparison

Parameter	5MT 3-R (Bel Fuse)	0234003.MXP (Littelfuse)	0232003.MXP (Littelfuse)	0239003.HXP (Littelfuse)	BK1/GMD-3-R (Eaton)
Current Rating	3 A	3 A	3 A	3 A	3 A
Voltage Rating (AC)	250 V	250 V	250 V	250 V	250 V
Fuse Type	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass	Cartridge, Glass
Package / Case	5mm x 20mm	5mm x 20mm	5mm x 20mm	5mm x 20mm	5mm x 20mm
Response Time	Medium Blow	Medium Blow	Medium Blow	Slow Blow	Slow Blow
Breaking Capacity @ Rated Voltage	100A	100A	100A	100A	100A
Operating Temperature Range	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C	-55°C ~ 125°C
Melting I²t	58	26.24	17.19	129.51	145
DC Cold Resistance	0.035 Ω	0.0431 Ω	0.0226 Ω	0.04877 Ω	0.0655 Ω
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Obsolete	Active	Active	Active	Active
Approval Agencies	CE, CSA, cURus, PSE	CE, CSA, K-MARK, PSE, UL	CE, KC, PSE	CE, CSA, KC, PSE, UL	CSA, PSE/JET, UL

Engineering Selection Recommendations

For Direct Replacement (Medium-Blow Response):

0234003.MXP (Littelfuse 234 Series) is the primary substitute for the 5MT 3-R. This part maintains identical response time characteristics and carries the broadest certification coverage (CE, CSA, K-MARK, PSE, UL). It is actively manufactured with substantial inventory availability (658 pcs).

0232003.MXP (Littelfuse 232 Series) provides an alternative medium-blow option with the highest inventory level (8421 pcs) and lowest DC cold resistance (0.0226 Ω). Certification coverage includes CE, KC, and PSE.

For Slow-Blow Applications:

0239003.HXP (Littelfuse 239 Series) and BK1/GMD-3-R (Eaton GMD Series) are suitable only when slow-blow response is functionally acceptable. These parts exhibit significantly higher melting I²t values (129.51 and 145 respectively), resulting in delayed trip times under transient overcurrent conditions. Both carry comprehensive certifications and active product status.

Certification Alignment:

All substitutes maintain ROHS3 compliance and REACH unaffected status. Selection should prioritize parts matching the original system's certification requirements. The 0234003.MXP includes UL certification, beneficial for North American applications. The BK1/GMD-3-R includes PSE/JET certification, suitable for Japanese market applications.

Frequently Asked Questions (FAQ)

Q: Can 0232003.MXP replace 5MT 3-R in all applications?

A: Yes, provided the application tolerates the lower melting I²t value (17.19 vs. 58). The 0232003.MXP will trip faster under sustained overcurrent due to reduced thermal mass. Verify system protection curves before substitution.

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

A: Medium-blow fuses (5MT 3-R, 0234003.MXP, 0232003.MXP) respond quickly to overcurrent. Slow-blow fuses (0239003.HXP, BK1/GMD-3-R) tolerate brief inrush currents and trip only under sustained overcurrent. Slow-blow fuses have higher melting I²t values, requiring longer heating time for activation.

Q: Are all substitutes physically compatible with the original holder?

A: Yes. All substitutes maintain the 5mm x 20mm cartridge package and require the same holder type. Physical installation is identical.

Q: Which substitute has the best availability?

A: 0232003.MXP (Littelfuse 232 Series) has the highest inventory level at 8421 pcs. 0234003.MXP (658 pcs) and 0239003.HXP (2802 pcs) also maintain substantial stock.

Q: Can I use a slow-blow fuse where a medium-blow was originally specified?

A: Only if system protection requirements permit delayed response to overcurrent. Slow-blow fuses are designed for circuits with inrush currents (motors, transformers). Verify protection coordination with upstream devices before substitution.

Q: What certifications should I prioritize for my application?

A: Match certifications to your target market. UL certification (0234003.MXP, 0239003.HXP) is required for North American applications. PSE/JET certification (BK1/GMD-3-R) is required for Japanese applications. CE certification is required for European markets (all substitutes qualify).

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