Bel Fuse Inc. 5ST 6.3 Glass Cartridge Fuse - Equivalent & Substitute Parts

Part Overview

The Bel Fuse Inc. 5ST 6.3 is a 6.3 A, 250 V AC/DC slow-blow glass cartridge fuse in 5mm x 20mm form factor, designed for circuit protection in industrial and commercial applications. This part carries an obsolete product status, making identification of active equivalent and substitute parts essential for ongoing system maintenance, repairs, and new designs requiring compatible protection devices.

Key Parameters

Parameter	Value
Current Rating	6.3 A
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Package / Case	5mm x 20mm
Response Time	Slow Blow
Mounting Type	Requires Holder
Breaking Capacity @ Rated Voltage	63 A
Operating Temperature Range	-55°C to 125°C

Substitute Part Grouping Explanation

Substitution of the obsolete 5ST 6.3 is determined by strict equivalence across the following critical parameters:

Current Rating: 6.3 A (exact match required)
Voltage Rating: 250 V AC (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Package / Case: 5mm x 20mm (exact match required)
Response Time: Slow Blow (exact match required)
Mounting Type: Requires Holder (exact match required)

Parts are grouped into two categories:

Direct Manufacturer Equivalents: Parts from Bel Fuse Inc., Littelfuse Inc., and SCHURTER Inc. that match all critical parameters and maintain identical breaking capacity (63 A) and melting I²t characteristics within acceptable engineering tolerances.

Parametric Equivalent: The 5ET 6.3-R from Bel Fuse Inc. matches all critical parameters but features enhanced breaking capacity (150 A) and higher melting I²t (658 vs. 160), suitable for applications requiring higher fault current protection margins.

Parameter Comparison

Part Number	Manufacturer	Current (A)	Voltage (V AC)	Package	Response Time	Breaking Capacity (A)	Melting I²t	DC Cold Resistance (Ω)	Product Status	RoHS Status
5ST 6.3	Bel Fuse Inc.	6.3	250	5x20mm	Slow Blow	63	160	0.008	Obsolete	Non-compliant
5ST 6.3-R	Bel Fuse Inc.	6.3	250	5x20mm	Slow Blow	63	160	0.008	Active	ROHS3 Compliant
5ET 6.3-R	Bel Fuse Inc.	6.3	250	5x20mm	Slow Blow	150	658	0.009	Active	ROHS3 Compliant
0034.3125	SCHURTER Inc.	6.3	250	5x20mm	Slow Blow	63	190	—	Active	ROHS3 Compliant
021806.3MXBP	Littelfuse Inc.	6.3	250	5x20mm	Slow Blow	63	198.5	0.0076	Active	ROHS3 Compliant
021806.3VXP	Littelfuse Inc.	6.3	250	5x20mm	Slow Blow	63	198.5	0.0076	Active	ROHS3 Compliant
021806.3HXP	Littelfuse Inc.	6.3	250	5x20mm	Slow Blow	63	198.5	0.0076	Active	ROHS3 Compliant
021806.3MXF11P	Littelfuse Inc.	6.3	250	5x20mm	Slow Blow	63	198.5	0.0076	Active	ROHS3 Compliant
021806.3MXF34P	Littelfuse Inc.	6.3	250	5x20mm	Slow Blow	63	198.5	0.0076	Active	ROHS3 Compliant
021806.3MXP	Littelfuse Inc.	6.3	250	5x20mm	Slow Blow	63	198.5	0.0076	Active	ROHS3 Compliant
021806.3TXP	Littelfuse Inc.	6.3	250	5x20mm	Slow Blow	63	198.5	0.0076	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: 5ST 6.3-R (Bel Fuse Inc.)

The 5ST 6.3-R is the direct active equivalent to the obsolete 5ST 6.3. It maintains identical electrical and mechanical specifications, including current rating, voltage rating, breaking capacity, and melting I²t. The part is ROHS3 compliant and carries active product status with extensive inventory availability (26,139 pcs). Approval agencies include CCC, CE, CSA, cURus, IMQ, SEMKO, and VDE, providing broad regulatory coverage.

Secondary Recommendation: Littelfuse 218 Series (021806.3MXBP, 021806.3VXP, 021806.3HXP, 021806.3MXF11P, 021806.3MXF34P, 021806.3MXP, 021806.3TXP)

All Littelfuse 218 series parts meet the critical electrical and mechanical parameters. These parts feature slightly elevated melting I²t values (198.5 vs. 160) and marginally lower DC cold resistance (0.0076 Ω vs. 0.008 Ω), representing minor performance variations within acceptable engineering tolerances. All carry ROHS3 compliance and active product status. Approval agencies include CCC, CE, CSA, K-MARK, PSE, SEMKO, UL, and VDE.

Tertiary Recommendation: SCHURTER 0034.3125 (FST 5x20 Series)

The SCHURTER 0034.3125 provides direct parameter equivalence with melting I²t of 190 and identical breaking capacity of 63 A. Physical dimensions are 5.20mm diameter (vs. 5.10mm for the original), representing a negligible tolerance variation. ROHS3 compliant with active status. Approval agencies include CCC, cURus, PSE/JET, and VDE.

Enhanced Protection Option: 5ET 6.3-R (Bel Fuse Inc.)

The 5ET 6.3-R maintains all critical electrical and mechanical parameters but provides enhanced breaking capacity (150 A vs. 63 A) and significantly higher melting I²t (658 vs. 160). This part is suitable for applications requiring higher fault current margins or where system fault levels exceed the original design specification. ROHS3 compliant with active status and broad regulatory approval.

Frequently Asked Questions (FAQ)

Q: Can I use the 5ET 6.3-R as a direct replacement for the 5ST 6.3?

A: Yes. The 5ET 6.3-R matches all critical parameters: 6.3 A current rating, 250 V AC voltage rating, 5x20mm package, slow-blow response, and cartridge glass type. The enhanced breaking capacity (150 A) and melting I²t (658) provide additional protection margin without affecting normal circuit operation. This substitution is suitable for all applications where the original 5ST 6.3 was specified.

Q: What is the difference between the Littelfuse 218 series variants (MXBP, VXP, HXP, MXF11P, MXF34P, MXP, TXP)?

A: All Littelfuse 218 series variants listed maintain identical electrical specifications: 6.3 A, 250 V AC, 5x20mm package, slow-blow response, and 63 A breaking capacity. The letter designations (MXBP, VXP, HXP, etc.) indicate internal construction or approval agency variations. All are electrically and mechanically interchangeable for the 5ST 6.3 application.

Q: Does the SCHURTER 0034.3125 fit in the same holder as the original 5ST 6.3?

A: Yes. The SCHURTER 0034.3125 is specified for 5x20mm package holders. Physical diameter is 5.20mm (vs. 5.10mm for the original), representing a 0.10mm tolerance variation within standard mechanical clearances for cartridge fuse holders.

Q: Are all substitute parts RoHS compliant?

A: Yes. All active substitute parts listed carry ROHS3 compliance. The original 5ST 6.3 is marked as RoHS non-compliant due to its obsolete status. All recommended substitutes meet current RoHS requirements.

Q: Which substitute part has the highest inventory availability?

A: The 5ET 6.3-R from Bel Fuse Inc. carries the highest inventory with 64,646 pcs in stock, followed by the 5ST 6.3-R with 26,139 pcs. Littelfuse 218 series parts range from 709 to 2,743 pcs, and SCHURTER 0034.3125 has 59,595 pcs available.

Q: Can I mix different substitute parts in the same circuit or system?

A: Yes. All listed substitute parts meet identical critical parameters and are mechanically and electrically interchangeable. However, for consistency in maintenance and spare parts management, using a single substitute part number across a system is recommended.

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