MS 3 Board Mount Fuse Equivalent & Substitute Parts

Part Overview

The MS 3 is a 3 A, 125 V AC/DC board mount axial fuse manufactured by Bel Fuse Inc. This component is classified as obsolete, making identification of equivalent substitute parts essential for ongoing system maintenance and new design implementations. The MS 3 serves as a protective device in electronic circuits requiring slow-blow response characteristics and through-hole axial mounting configuration.

Key Parameters

Parameter	Value
Current Rating	3 A
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Slow Blow
Mounting Type	Through Hole
Package Type	Axial
Breaking Capacity @ Rated Voltage	50 A AC, 300 A DC
Operating Temperature Range	-55°C to 125°C
Size / Dimension	0.125" Dia x 0.280" L (3.18 mm x 7.10 mm)

Substitute Part Grouping Explanation

Substitute parts for the MS 3 are identified based on the following critical parameters that determine functional equivalence:

Current Rating: 3 A (exact match required)
Voltage Rating: 125 V AC and 125 V DC (exact match required)
Response Time: Slow Blow (exact match required)
Mounting Type: Through Hole (exact match required)
Package Type: Axial (exact match required)
Breaking Capacity: Minimum 50 A AC capability
Operating Temperature Range: Must encompass -55°C to 125°C

Two substitute parts meet these criteria: the Littelfuse 0473003.MRT1L and 0473003.YRT1L, both from the PICO® II 473 series. These components are active products with current manufacturing status and full compliance certifications.

The SCHURTER 0034.6981 does not qualify as a direct substitute due to differences in current rating (4 A vs. 3 A), voltage rating (250 V vs. 125 V), and package configuration (radial vs. axial).

Parameter Comparison

Parameter	MS 3 (Bel Fuse)	0473003.MRT1L (Littelfuse)	0473003.YRT1L (Littelfuse)
Current Rating (Amps)	3 A	3 A	3 A
Voltage Rating - AC	125 V	125 V	125 V
Voltage Rating - DC	125 V	125 V	125 V
Response Time	Slow Blow	Slow Blow	Slow Blow
Mounting Type	Through Hole	Through Hole	Through Hole
Package / Case	Axial	Axial	Axial
Breaking Capacity @ Rated Voltage	50 A AC, 300 A DC	50 A	50 A
Operating Temperature Range	-55°C to 125°C	-55°C to 125°C	-55°C to 125°C
Size / Dimension	0.125" Dia x 0.280" L (3.18 mm x 7.10 mm)	0.135" Dia x 0.280" L (3.43 mm x 7.11 mm)	0.135" Dia x 0.280" L (3.43 mm x 7.11 mm)
DC Cold Resistance	0.056 Ohms	0.038 Ohms	0.038 Ohms
Melting I²t	8	21	21
Product Status	Obsolete	Active	Active
Approval Agency	CE, CSA, cURus	CSA, PSE, UR	CSA, PSE, UR
RoHS Status	Not specified	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

The Littelfuse 0473003.MRT1L and 0473003.YRT1L are functionally equivalent substitutes for the obsolete MS 3. Both parts are active products with current manufacturing support and inventory availability.

Selection between the two Littelfuse options is based on packaging preference: 0473003.MRT1L is supplied in Cut Tape (CT) with 2,400 pieces in stock, while 0473003.YRT1L is also supplied in Cut Tape (CT) with 20,100 pieces in stock. Both carry ROHS3 compliance and CSA/PSE/UR certifications, meeting modern regulatory requirements.

Minor dimensional variations exist: the Littelfuse substitutes have a slightly larger diameter (0.135" vs. 0.125") and lower DC cold resistance (0.038 Ohms vs. 0.056 Ohms). These differences do not affect functional compatibility in standard board mount applications.

Frequently Asked Questions (FAQ)

Q: Can the SCHURTER 0034.6981 be used as a substitute for the MS 3?

A: No. The SCHURTER part operates at 4 A and 250 V, which exceeds the MS 3 specifications of 3 A and 125 V. Additionally, it uses radial mounting configuration rather than axial. This part is not functionally equivalent.

Q: What is the difference between the two Littelfuse substitute options?

A: Both 0473003.MRT1L and 0473003.YRT1L are electrically and mechanically identical. The primary difference is inventory availability: 0473003.YRT1L has significantly higher stock (20,100 pieces vs. 2,400 pieces). Both are supplied in Cut Tape packaging.

Q: Are there dimensional compatibility concerns with the Littelfuse substitutes?

A: The Littelfuse substitutes have a slightly larger diameter (0.135" vs. 0.125") and identical length (0.280"). PCB through-hole spacing must accommodate the 0.135" diameter. Verify board layout compatibility before implementation.

Q: Do the substitute parts meet current compliance standards?

A: Yes. Both Littelfuse substitutes are ROHS3 compliant and carry CSA, PSE, and UR certifications. The original MS 3 carried CE, CSA, and cURus certifications. Littelfuse substitutes meet modern regulatory requirements for new designs.

Q: What is the significance of the different melting I²t values?

A: The MS 3 has a melting I²t of 8, while the Littelfuse substitutes have a melting I²t of 21. This indicates the Littelfuse parts have a higher thermal capacity before melting. Both maintain the same 3 A current rating and slow-blow response time, ensuring equivalent circuit protection behavior.

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