SCHURTER 0034.3776 Glass Cartridge Fuse 1.25A 250VAC 5x20mm Equivalent & Substitute Parts

Part Overview

The SCHURTER 0034.3776 is a 1.25A 250VAC glass cartridge fuse in 5x20mm form factor, designed for circuit protection in AC/DC applications. This slow-blow fuse cartridge requires a holder for installation and is actively manufactured. Equivalent and substitute parts are necessary when the primary part is unavailable, when alternative certifications are required for specific markets, or when different electrical characteristics better suit application requirements.

Key Parameters

Parameter	Value
Manufacturer Part Number	0034.3776
Manufacturer	SCHURTER Inc.
Current Rating	1.25 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	100A
Operating Temperature Range	-40°C ~ 85°C
Product Status	Active
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitute parts for the SCHURTER 0034.3776 are grouped based on strict electrical and mechanical parameter matching:

Primary Substitution Criteria:

Current Rating: 1.25 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)
Response Time: Slow Blow (exact match required)
Mounting Type: Requires Holder (exact match required)

Secondary Differentiation Parameters:

Breaking Capacity @ Rated Voltage (varies: 35A, 100A, 150A)
Melting I²t (varies: 1.54 to 33.3)
Operating Temperature Range (varies: -40°C ~ 85°C to -55°C ~ 125°C)
DC Cold Resistance (varies: 0.0446 to 0.206 Ohms)
Approval Agencies (varies by manufacturer and series)

All substitute parts listed maintain identical primary electrical and mechanical specifications, ensuring direct functional compatibility within the 5x20mm cartridge fuse category.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating (A)	Voltage (V AC)	Package	Response Time	Breaking Capacity (A)	Melting I²t	Operating Temp (°C)	DC Cold Resistance (Ω)	Approvals
0034.3776	SCHURTER Inc.	FSL 5x20	1.25	250	5x20mm	Slow Blow	100	1.54	-40 ~ 85	—	cULus
0034.5044	SCHURTER Inc.	FTT 5x20	1.25	250	5x20mm	Slow Blow	35	33.3	-40 ~ 85	—	cURus
02391.25MXP	Littelfuse Inc.	239	1.25	250	5x20mm	Slow Blow	100	19.525	-55 ~ 125	0.198	CE, CSA, KC, PSE, UL
02131.25MXP	Littelfuse Inc.	213	1.25	250	5x20mm	Slow Blow	35	27.15	-55 ~ 125	0.0817	BSI, CCC, CE, CSA, PSE, SEMKO, UR, VDE
02181.25HXP	Littelfuse Inc.	218	1.25	250	5x20mm	Slow Blow	35	12.65	-55 ~ 125	0.0446	CCC, CE, CSA, K-MARK, PSE, SEMKO, UL, VDE
02191.25MXAP	Littelfuse Inc.	219XA	1.25	250	5x20mm	Slow Blow	150	27.15	-55 ~ 125	0.0817	CCC, CE, CSA, PSE, SEMKO, UL, VDE
5TT 1.25-R	Bel Fuse Inc.	5TT	1.25	250	5x20mm	Slow Blow	100	13.1	-55 ~ 125	0.206	CE, CSA, cULus, PSE

Engineering Selection Recommendations

Selection of substitute parts should be based on the following criteria:

For Direct Replacement (Identical Electrical Characteristics):

SCHURTER 0034.5044 provides parametric equivalence within the SCHURTER product line, maintaining the same operating temperature range as the primary part.
Littelfuse 02391.25MXP and Bel Fuse 5TT 1.25-R both match the 100A breaking capacity of the primary part, suitable for applications requiring identical fault current handling.

For Extended Temperature Range Applications:

Littelfuse 02131.25MXP, 02181.25HXP, 02191.25MXAP, and Bel Fuse 5TT 1.25-R all support -55°C ~ 125°C operating range, exceeding the primary part's -40°C ~ 85°C specification.

For Specific Certification Requirements:

Littelfuse 02131.25MXP offers the broadest certification coverage (BSI, CCC, CE, CSA, PSE, SEMKO, UR, VDE), suitable for multi-market applications.
Littelfuse 02181.25HXP includes K-MARK certification for Korean market compliance.
Littelfuse 02191.25MXAP provides 150A breaking capacity with comprehensive international certifications.

For Lower DC Cold Resistance:

Littelfuse 02181.25HXP (0.0446 Ω) offers the lowest DC cold resistance, beneficial for applications sensitive to resistive heating.

All substitute parts maintain active product status and ROHS3 compliance, ensuring long-term availability and environmental regulatory conformance.

Frequently Asked Questions (FAQ)

Q: Can I use a substitute part with a different breaking capacity? A: Yes. The breaking capacity (35A, 100A, or 150A) determines the maximum fault current the fuse can safely interrupt. Selection depends on the circuit's maximum available fault current. Higher breaking capacity provides greater safety margin in high-fault-current environments.

Q: What is the significance of melting I²t values? A: Melting I²t indicates the thermal energy required to melt the fuse element. Lower values result in faster response to overcurrent. The primary part (1.54) has the lowest I²t, providing the fastest response. Substitute parts with higher I²t values (up to 33.3) respond more slowly, suitable for circuits with higher inrush currents.

Q: Are all substitute parts compatible with existing 5x20mm fuse holders? A: Yes. All substitute parts use the 5x20mm cartridge form factor and require a holder for installation. Physical dimensions are standardized across all listed parts, ensuring mechanical compatibility.

Q: Which substitute part should I choose for extreme temperature environments? A: Littelfuse 02131.25MXP, 02181.25HXP, 02191.25MXAP, and Bel Fuse 5TT 1.25-R all support -55°C ~ 125°C, compared to the primary part's -40°C ~ 85°C. These are suitable for industrial and automotive applications with wider temperature exposure.

Q: How do I select between Littelfuse and Bel Fuse alternatives? A: Both manufacturers provide equivalent electrical performance. Selection depends on certification requirements, supply chain availability, and regional market preferences. Littelfuse offers broader certification coverage, while Bel Fuse 5TT 1.25-R provides cULus approval matching the primary part's certification body.

Q: What does DC Cold Resistance affect? A: DC Cold Resistance affects resistive heating during normal operation. Lower resistance (0.0446 Ω in 02181.25HXP) generates less heat, beneficial for continuous-duty applications. Higher resistance (0.206 Ω in 5TT 1.25-R) is acceptable for intermittent-duty circuits.

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