Equivalent & Substitute Parts for 5ST 2.5 Glass Cartridge Fuse

Part Overview

The Bel Fuse Inc. 5ST 2.5 is a 2.5 A, 250 V AC/DC glass cartridge fuse in 5mm x 20mm form factor with slow-blow response characteristics. This part is classified as obsolete, necessitating identification of active equivalent and substitute components that maintain electrical and mechanical compatibility. Substitute parts must match the core electrical parameters: 2.5 A current rating, 250 V voltage rating, 5mm x 20mm package dimensions, and slow-blow response time. The part requires a fuse holder for installation.

Key Parameters

Parameter	Value
Current Rating	2.5 A
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Package / Case	5mm x 20mm
Response Time	Slow Blow
Mounting Type	Requires Holder
Operating Temperature Range	-55°C to 125°C
Breaking Capacity @ Rated Voltage	35 A

Substitute Part Grouping Explanation

Substitute parts are classified into two categories based on electrical equivalence:

Direct Manufacturer Equivalents maintain identical electrical characteristics to the 5ST 2.5, including breaking capacity of 35 A and melting I²t of 20. These parts are functionally interchangeable without circuit redesign:

5ST 2.5-R (Bel Fuse Inc.)
0034.3121 (SCHURTER Inc.)
021802.5MXBP, 021802.5MXP, 021802.5VXP, 021802.5HXP, 021802.5MXF11P, 021802.5MXF5P (Littelfuse Inc.)

Parametric Equivalents share the same current, voltage, and package specifications but differ in breaking capacity and melting I²t characteristics. These parts are electrically compatible for the specified 2.5 A, 250 V application but exhibit different fault-clearing behavior:

5ET 2.5-R (Bel Fuse Inc.) – Breaking capacity 150 A, melting I²t 137
5TT 2.5-R (Bel Fuse Inc.) – Breaking capacity 100 A, melting I²t 45

All substitute parts maintain the required 5mm x 20mm physical dimensions, slow-blow response time, and -55°C to 125°C operating temperature range.

Parameter Comparison

Manufacturer Part Number	Manufacturer	Current Rating (A)	Voltage Rating (V AC)	Breaking Capacity (A)	Melting I²t	Package	Response Time	Product Status	RoHS Status
5ST 2.5	Bel Fuse Inc.	2.5	250	35	20	5mm x 20mm	Slow Blow	Obsolete	Non-compliant
5ST 2.5-R	Bel Fuse Inc.	2.5	250	35	20	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
5ET 2.5-R	Bel Fuse Inc.	2.5	250	150	137	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
5TT 2.5-R	Bel Fuse Inc.	2.5	250	100	45	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
0034.3121	SCHURTER Inc.	2.5	250	35	21.9	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
021802.5MXBP	Littelfuse Inc.	2.5	250	35	23.25	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
021802.5MXP	Littelfuse Inc.	2.5	250	35	23.25	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
021802.5VXP	Littelfuse Inc.	2.5	250	35	23.25	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
021802.5HXP	Littelfuse	2.5	250	35	23.25	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
021802.5MXF11P	Littelfuse Inc.	2.5	250	35	23.25	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant
021802.5MXF5P	Littelfuse Inc.	2.5	250	35	23.25	5mm x 20mm	Slow Blow	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: 5ST 2.5-R

The 5ST 2.5-R from Bel Fuse Inc. is the direct active equivalent of the obsolete 5ST 2.5. It maintains identical electrical specifications (35 A breaking capacity, 20 melting I²t) and is ROHS3 compliant. This part provides the most direct replacement path with no circuit redesign required.

Secondary Recommendations: Littelfuse 218 Series (021802.5MXP, 021802.5HXP, 021802.5MXF11P, 021802.5MXF5P)

These Littelfuse parts are direct electrical equivalents with 35 A breaking capacity and 23.25 melting I²t. All are ROHS3 compliant and carry comprehensive international certifications (CCC, CE, CSA, K-MARK, PSE, SEMKO, UL, VDE). The 021802.5MXP variant offers the highest inventory availability (11,400 units).

Alternative Recommendation: SCHURTER 0034.3121

The SCHURTER FST 5x20 series part 0034.3121 provides direct electrical equivalence with 35 A breaking capacity and 21.9 melting I²t. It is ROHS3 compliant and carries CCC, cURus, PSE/JET, and VDE certifications.

Parametric Alternatives: 5ET 2.5-R and 5TT 2.5-R

These Bel Fuse parts maintain the 2.5 A, 250 V, 5mm x 20mm specifications but feature higher breaking capacities (150 A and 100 A respectively) and elevated melting I²t values. Selection of these parts requires circuit analysis to confirm that the increased fault-clearing characteristics are compatible with the application.

Frequently Asked Questions (FAQ)

Q: Can I use 5ST 2.5-R as a direct replacement for the obsolete 5ST 2.5?

A: Yes. The 5ST 2.5-R is the active equivalent with identical electrical specifications, including 2.5 A current rating, 250 V voltage rating, 35 A breaking capacity, and 20 melting I²t. Both parts use the same 5mm x 20mm package and require the same fuse holder.

Q: What is the difference between direct equivalents and parametric equivalents?

A: Direct equivalents (5ST 2.5-R, Littelfuse 218 series, SCHURTER 0034.3121) maintain identical breaking capacity and melting I²t characteristics. Parametric equivalents (5ET 2.5-R, 5TT 2.5-R) match the current, voltage, and package specifications but have different fault-clearing behavior due to higher breaking capacities and melting I²t values.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All active substitute parts listed are ROHS3 compliant. The original 5ST 2.5 is RoHS non-compliant, making the transition to compliant alternatives necessary for new designs and regulatory compliance.

Q: Do all substitute parts fit the same fuse holder?

A: Yes. All substitute parts maintain the 5mm x 20mm physical dimensions and are designed for standard 5x20mm fuse holders. No mechanical modifications are required.

Q: Which substitute part has the best inventory availability?

A: The Littelfuse 021802.5MXP offers the highest inventory with 11,400 units in stock, followed by 021802.5HXP with 21,272 units. Both are direct electrical equivalents suitable for immediate deployment.

Q: What certifications should I verify for my application?

A: All substitute parts carry international certifications including CE, CSA, and VDE. Specific requirements depend on your application region. Littelfuse parts carry the broadest certification set (CCC, CE, CSA, K-MARK, PSE, SEMKO, UL, VDE), making them suitable for global applications.

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