SCHURTER 0034.3973 Glass Cartridge Fuse 125mA 250VAC 5x20mm Equivalent & Substitute Parts

Part Overview

The SCHURTER 0034.3973 is a 125mA 250VAC glass cartridge fuse in 5x20mm form factor, classified as obsolete. This fuse requires a holder for installation and is designed for slow-blow response characteristics. Due to its obsolete product status, equivalent and substitute parts from active product lines are necessary for ongoing system maintenance and new designs requiring compatible fuse protection.

Key Parameters

Parameter	Value
Current Rating	125 mA
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Package / Case	5mm x 20mm
Response Time	Slow Blow
Breaking Capacity @ Rated Voltage	35A
Mounting Type	Requires Holder
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following parameters: current rating (125mA), voltage rating (250VAC), fuse type (cartridge glass), physical package (5x20mm), response time (slow blow), breaking capacity (35A), and mounting requirement (holder-based). All substitute parts listed maintain these core electrical and mechanical specifications. Variations in melting I²t values, operating temperature ranges, and approval certifications are documented but do not disqualify substitution when the primary parameters align.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating	Voltage Rating	Response Time	Melting I²t	Operating Temperature	Product Status	Approval Agency
0034.3973	SCHURTER Inc.	FSD 5x20	125 mA	250 V AC	Slow Blow	0.084	Not specified	Obsolete	CSA, UL
0034.3108	SCHURTER Inc.	FST 5x20	125 mA	250 V AC	Slow Blow	0.064	-55°C ~ 125°C	Active	CCC, cURus, VDE
0034.3763	SCHURTER Inc.	FSL 5x20	125 mA	250 V AC	Slow Blow	0.161	-40°C ~ 85°C	Active	cULus
0034.5034	SCHURTER Inc.	FTT 5x20	125 mA	250 V AC	Slow Blow	0.259	-40°C ~ 85°C	Active	cURus
0034.5608.11	SCHURTER Inc.	SMD-FST	125 mA	250 V AC	Slow Blow	0.064	-55°C ~ 125°C	Active	cURus, VDE
0239.125MXP	Littelfuse Inc.	239	125 mA	250 V AC	Slow Blow	0.085	-55°C ~ 125°C	Active	CE, UL
0218.125HXP	Littelfuse Inc.	218	125 mA	250 V AC	Slow Blow	0.1465	-55°C ~ 125°C	Active	CCC, CE, CSA, K-MARK, SEMKO, UL, VDE
0218.125MX8810P	Littelfuse Inc.	218	125 mA	250 V AC	Slow Blow	0.1465	-55°C ~ 125°C	Active	CCC, CE, CSA, K-MARK, SEMKO, UL, VDE
0218.125MXBP	Littelfuse Inc.	218	125 mA	250 V AC	Slow Blow	0.1465	-55°C ~ 125°C	Active	CCC, CE, CSA, KC, SEMKO, UL, VDE
0218.125MXP	Littelfuse Inc.	218	125 mA	250 V AC	Slow Blow	0.1465	-55°C ~ 125°C	Active	CCC, CE, CSA, K-MARK, SEMKO, UL, VDE
0218.125TXP	Littelfuse Inc.	218	125 mA	250 V AC	Slow Blow	0.1465	-55°C ~ 125°C	Active	CCC, CE, CSA, KC, SEMKO, UL, VDE

Engineering Selection Recommendations

All listed substitute parts maintain electrical and mechanical compatibility with the original 0034.3973 specification. SCHURTER active alternatives (0034.3108, 0034.3763, 0034.5034, 0034.5608.11) provide direct product line continuity with expanded operating temperature ranges and current regulatory certifications. Littelfuse 218 and 239 series parts (0218.125HXP, 0218.125MX8810P, 0218.125MXBP, 0218.125MXP, 0218.125TXP, 0239.125MXP) offer cross-manufacturer equivalence with comprehensive international approval coverage including CCC, CE, CSA, K-MARK, SEMKO, UL, and VDE certifications. Selection should prioritize parts with active product status and certifications matching the target application's regulatory requirements.

Frequently Asked Questions (FAQ)

Q: Can SCHURTER 0034.3108 directly replace the obsolete 0034.3973? A: Yes. Both parts share identical current rating (125mA), voltage rating (250VAC), fuse type (cartridge glass), package (5x20mm), response time (slow blow), and breaking capacity (35A). The 0034.3108 is active and carries expanded certifications (CCC, cURus, VDE) with extended operating temperature range (-55°C to 125°C).

Q: What is the difference between SCHURTER FST, FSL, and FTT series fuses? A: All three series maintain the same electrical specifications (125mA, 250VAC, 5x20mm, slow blow). The primary difference is melting I²t value: FST (0.064), FSL (0.161), and FTT (0.259). These variations affect thermal response characteristics but do not change substitution eligibility when core parameters align.

Q: Are Littelfuse 218 series parts compatible with SCHURTER fuse holders? A: Yes. Littelfuse 218 series parts (0218.125HXP, 0218.125MX8810P, 0218.125MXBP, 0218.125MXP, 0218.125TXP) maintain the 5x20mm physical package and all electrical specifications required for holder compatibility. Cross-manufacturer substitution is valid based on package and electrical equivalence.

Q: Does melting I²t variation affect substitution suitability? A: Melting I²t values vary across substitute parts (0.064 to 0.259) but do not disqualify substitution when all primary parameters (current, voltage, package, response time, breaking capacity) remain constant. Application-specific thermal requirements should guide final selection.

Q: Which substitute part has the broadest regulatory approval coverage? A: Littelfuse 218 series parts (0218.125HXP, 0218.125MX8810P, 0218.125MXBP, 0218.125MXP, 0218.125TXP) carry the most comprehensive certifications: CCC, CE, CSA, K-MARK, SEMKO, UL, and VDE. These certifications support global market deployment.

Q: Is the SCHURTER 0034.5608.11 (SMD-FST) suitable for standard fuse holder applications? A: Yes. Despite the SMD designation in the series name, the 0034.5608.11 maintains the standard 5x20mm package and requires a holder for installation, making it compatible with existing holder-based applications.

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