Equivalent & Substitute Parts for 5ET 1.25

Part Overview

The Bel Fuse Inc. 5ET 1.25 is a 1.25 A, 250 V AC/DC glass cartridge fuse with a 5mm x 20mm form factor, designed for applications requiring slow-blow response characteristics. This part is classified as obsolete, necessitating identification of active equivalent and substitute components that maintain electrical and mechanical compatibility while meeting current regulatory requirements.

Key Parameters

Parameter	Value
Current Rating	1.25 A
Voltage Rating (AC)	250 V
Response Time	Slow Blow
Package / Case	5mm x 20mm
Fuse Type	Cartridge, Glass
Mounting Type	Requires Holder
Breaking Capacity @ Rated Voltage	150 A
Melting I²t	42
Operating Temperature Range	-55°C ~ 125°C

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following critical parameters:

Current Rating: 1.25 A (exact match required)
Voltage Rating (AC): 250 V (exact match required)
Response Time: Slow Blow (exact match required)
Package / Case: 5mm x 20mm (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Mounting Type: Requires Holder (exact match required)

Parts are grouped into two categories:

Direct Manufacturer Equivalent: 5ET 1.25-R (Bel Fuse Inc.) — identical series with active product status and RoHS3 compliance.

Parametric Equivalents: 5ST 1.25-R and 5TT 1.25-R (Bel Fuse Inc.) — same electrical ratings and mechanical form factor but with different breaking capacity and melting I²t characteristics, suitable for applications where these parameters are not critical constraints.

Similar Parts from Alternative Manufacturers: Littelfuse Inc. (02131.25MXP, 02181.25TXP, 02191.25MXAP, 02391.25HXP), Eaton Electronics Division (BK1/GMD-1.25-R, GDC-1.25A) — meet all core electrical and mechanical requirements with active product status and RoHS3 compliance.

Parameter Comparison

Part Number	Manufacturer	Current Rating (A)	Voltage (V AC)	Response Time	Package	Breaking Capacity (A)	Melting I²t	Product Status	RoHS Status
5ET 1.25	Bel Fuse Inc.	1.25	250	Slow Blow	5mm x 20mm	150	42	Obsolete	Non-compliant
5ET 1.25-R	Bel Fuse Inc.	1.25	250	Slow Blow	5mm x 20mm	150	42	Active	RoHS3 Compliant
5ST 1.25-R	Bel Fuse Inc.	1.25	250	Slow Blow	5mm x 20mm	35	4.1	Active	RoHS3 Compliant
5TT 1.25-R	Bel Fuse Inc.	1.25	250	Slow Blow	5mm x 20mm	100	13.1	Active	RoHS3 Compliant
02131.25MXP	Littelfuse Inc.	1.25	250	Slow Blow	5mm x 20mm	35	27.15	Active	RoHS3 Compliant
02181.25TXP	Littelfuse Inc.	1.25	250	Slow Blow	5mm x 20mm	35	12.65	Active	RoHS3 Compliant
02191.25MXAP	Littelfuse Inc.	1.25	250	Slow Blow	5mm x 20mm	150	27.15	Active	RoHS3 Compliant
02391.25HXP	Littelfuse Inc.	1.25	250	Slow Blow	5mm x 20mm	100	19.525	Active	RoHS3 Compliant
BK1/GMD-1.25-R	Eaton - Electronics Division	1.25	250	Slow Blow	5mm x 20mm	100	16	Active	RoHS3 Compliant
GDC-1.25A	Eaton - Electronics Division	1.25	250	Slow Blow	5mm x 20mm	35	10.05	Active	RoHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: 5ET 1.25-R (Bel Fuse Inc.) is the direct active equivalent, maintaining identical electrical characteristics and breaking capacity while achieving RoHS3 compliance and active product status. This part is the preferred replacement for direct substitution.

Secondary Recommendations: 02191.25MXAP (Littelfuse Inc.) provides equivalent breaking capacity (150 A) and is widely certified across regulatory agencies (CCC, CE, CSA, PSE, SEMKO, UL, VDE). BK1/GMD-1.25-R (Eaton Electronics Division) offers 100 A breaking capacity with active status and established certifications (CSA, PSE/JET, UL).

Alternative Selections: 5ST 1.25-R, 5TT 1.25-R, 02131.25MXP, 02181.25TXP, 02391.25HXP, and GDC-1.25A are suitable for applications where reduced breaking capacity does not present a constraint. All listed alternatives maintain active product status and RoHS3 compliance.

Frequently Asked Questions (FAQ)

Q: Can I use 5ST 1.25-R as a direct replacement for 5ET 1.25?

A: 5ST 1.25-R matches all core electrical and mechanical parameters (1.25 A, 250 V, slow-blow, 5mm x 20mm). However, breaking capacity differs (35 A vs. 150 A). Use this part only if your application does not require 150 A breaking capacity.

Q: What is the difference between breaking capacity and melting I²t?

A: Breaking capacity specifies the maximum fault current the fuse can safely interrupt. Melting I²t indicates the thermal energy required to melt the fuse element. Both parameters are provided in the comparison table for engineering evaluation.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All active substitute parts listed are RoHS3 compliant. The original 5ET 1.25 is RoHS non-compliant due to its obsolete status.

Q: Do all substitute parts use the same 5mm x 20mm package?

A: Yes. All substitute parts maintain the 5mm x 20mm form factor and require the same holder type, ensuring mechanical compatibility.

Q: Which substitute offers the closest match to the original 5ET 1.25?

A: 5ET 1.25-R (Bel Fuse Inc.) is identical in all electrical and mechanical parameters, including 150 A breaking capacity and 42 melting I²t.

Q: Can I mix different manufacturers' fuses in the same circuit?

A: All listed parts meet the same electrical and mechanical specifications. However, follow your equipment manufacturer's guidance regarding component sourcing and qualification requirements.

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