Littelfuse 02391.25MXP Glass Cartridge Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 02391.25MXP is a 1.25 A, 250 V AC/DC slow blow glass cartridge fuse in 5mm x 20mm package format. This fuse is designed for circuit protection in applications requiring slow response characteristics and is actively manufactured. Equivalent and substitute parts are identified when component availability is limited, supply chain disruptions occur, or design flexibility permits selection from qualified alternatives meeting the same electrical and mechanical specifications.

Key Parameters

Parameter	Value
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
Operating Temperature Range	-55°C ~ 125°C
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following parameters: current rating (1.25 A), AC voltage rating (250 V), fuse type (cartridge glass), package dimensions (5mm x 20mm), response time (slow blow), and mounting configuration (requires holder). Parts are grouped into three categories:

Direct Manufacturer Equivalents share identical electrical and mechanical specifications with the main part, differing only in internal construction or packaging designation. These include Littelfuse 02391.25HXP and Bel Fuse 5TT 1.25-R.

Parametric Equivalents maintain all critical electrical parameters and package dimensions but may differ in breaking capacity, melting I²t, DC cold resistance, or approval agency certifications. These include Littelfuse 02131.25MXP, 02181.25HXP, 02181.25MXP, 02181.25TXP, and 02191.25MXAP.

Manufacturer Recommended Alternatives meet core electrical and mechanical requirements but introduce variations in response time classification or operating temperature range. These include SCHURTER 0034.2517, Bel Fuse 5ET 1.25-R, and Bel Fuse 5ST 1.25-R.

Parameter Comparison

Part Number	Manufacturer	Series	Current (A)	Voltage AC (V)	Response Time	Breaking Capacity (A)	Melting I²t	DC Cold Resistance (Ω)	Approval Agencies	Inventory (Pcs)
02391.25MXP	Littelfuse	239	1.25	250	Slow Blow	100	19.525	0.198	CE, CSA, KC, PSE, UL	1059
02391.25HXP	Littelfuse	239	1.25	250	Slow Blow	100	19.525	0.198	CE, CSA, KC, PSE, UL	881
02131.25MXP	Littelfuse	213	1.25	250	Slow Blow	35	27.15	0.0817	BSI, CCC, CE, CSA, PSE, SEMKO, UR, VDE	3448
02181.25HXP	Littelfuse	218	1.25	250	Slow Blow	35	12.65	0.0446	CCC, CE, CSA, K-MARK, PSE, SEMKO, UL, VDE	5238
02181.25MXP	Littelfuse	218	1.25	250	Slow Blow	35	12.65	0.0446	CCC, CE, CSA, K-MARK, PSE, SEMKO, UL, VDE	4296
02181.25TXP	Littelfuse	218	1.25	250	Slow Blow	35	12.65	0.0446	CCC, CE, CSA, KC, PSE, SEMKO, UL, VDE	1155
02191.25MXAP	Littelfuse	219XA	1.25	250	Slow Blow	150	27.15	0.0817	CCC, CE, CSA, PSE, SEMKO, UL, VDE	1587
5TT 1.25-R	Bel Fuse	5TT	1.25	250	Slow Blow	100	13.1	0.206	CE, CSA, cULus, PSE	1862
0034.2517	SCHURTER	FSM 5x20	1.25	250	Medium Blow	80	5.47	Not Specified	Not Specified	1618
5ET 1.25-R	Bel Fuse	5ET	1.25	250	Slow Blow	150	42	0.08	CCC, CE, CSA, cURus, SEMKO, VDE	11329
5ST 1.25-R	Bel Fuse	5ST	1.25	250	Slow Blow	35	4.1	0.06	CCC, CE, CSA, cURus, IMQ, SEMKO, VDE	12140

Engineering Selection Recommendations

Direct Equivalents (02391.25HXP, 5TT 1.25-R): These parts are functionally identical to the 02391.25MXP and provide the most straightforward substitution path. Both maintain 100 A breaking capacity and equivalent melting I²t characteristics. Selection between these options depends on certification requirements and supply availability.

Parametric Equivalents with Lower Breaking Capacity (02131.25MXP, 02181.25HXP, 02181.25MXP, 02181.25TXP, 5ST 1.25-R): These parts reduce breaking capacity to 35 A, suitable for applications where circuit fault current does not exceed this threshold. The Littelfuse 218 series (02181.25HXP, 02181.25MXP, 02181.25TXP) offers the lowest DC cold resistance (0.0446 Ω) and expanded certification coverage including K-MARK and VDE. The Bel Fuse 5ST 1.25-R provides the lowest melting I²t (4.1) and DC cold resistance (0.06 Ω).

Parametric Equivalents with Higher Breaking Capacity (02191.25MXAP, 5ET 1.25-R): These parts increase breaking capacity to 150 A, providing enhanced protection margin in high fault-current environments. Both maintain slow blow response time and extended operating temperature range (-55°C to 125°C). The 5ET 1.25-R offers the highest melting I²t (42) among all alternatives.

Manufacturer Recommended Alternative (0034.2517): The SCHURTER FSM 5x20 series differs in response time classification (medium blow versus slow blow) and introduces a 125 V DC rating. This part is suitable only when medium response characteristics are acceptable and DC voltage protection is required. Operating temperature range is restricted to -40°C to 85°C.

Frequently Asked Questions (FAQ)

Q: Can I substitute 02391.25MXP with 02181.25MXP? A: Yes. Both parts maintain 1.25 A current rating, 250 V AC voltage rating, slow blow response, and 5mm x 20mm package. The 02181.25MXP reduces breaking capacity from 100 A to 35 A and lowers DC cold resistance to 0.0446 Ω. Substitution is valid when circuit fault current does not exceed 35 A.

Q: What is the difference between Littelfuse and Bel Fuse alternatives? A: Both manufacturers produce functionally equivalent 1.25 A, 250 V AC slow blow cartridge fuses in 5mm x 20mm packages. Littelfuse parts (02391 series, 02131 series, 02181 series, 02191 series) and Bel Fuse parts (5TT, 5ET, 5ST series) differ in internal construction, melting I²t characteristics, DC cold resistance, and certification agency approvals. Selection depends on specific application requirements and regional compliance mandates.

Q: Why does 0034.2517 have a different response time classification? A: The SCHURTER 0034.2517 is classified as medium blow rather than slow blow. This affects the fuse's response to transient overcurrent conditions. Medium blow fuses respond faster than slow blow fuses. This part is suitable only when medium response characteristics align with circuit protection requirements.

Q: Can I use 5ET 1.25-R in place of 02391.25MXP? A: Yes. Both parts maintain 1.25 A current rating, 250 V AC voltage rating, slow blow response, and 5mm x 20mm package dimensions. The 5ET 1.25-R increases breaking capacity to 150 A and melting I²t to 42, providing enhanced protection margin. This substitution is valid across all applications where the main part is specified.

Q: What does breaking capacity mean in fuse selection? A: Breaking capacity is the maximum fault current the fuse can safely interrupt without rupturing or creating a hazard. The 02391.25MXP has 100 A breaking capacity. Substitutes with lower breaking capacity (35 A) are suitable only when circuit fault current remains below this threshold. Substitutes with higher breaking capacity (150 A) provide additional safety margin.

Q: Are all these parts RoHS3 compliant? A: Yes. All listed substitute parts are ROHS3 compliant. The 02391.25MXP and all direct and parametric equivalents meet RoHS3 requirements. REACH status is unaffected for all parts.

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