MS 4 Board Mount Axial Fuse Equivalent & Substitute Parts

Part Overview

The MS 4 is a board mount axial fuse manufactured by Bel Fuse Inc., rated for 4 A at 125 V AC/DC with slow blow response characteristics. This component is classified as obsolete, making equivalent substitute parts necessary for ongoing design support and procurement. The MS 4 serves applications requiring through-hole axial fuse protection in low-voltage circuits with moderate current demands.

Key Parameters

Parameter	Value
Current Rating	4 A
Voltage Rating (AC)	125 V
Voltage Rating (DC)	125 V
Response Time	Slow Blow
Mounting Type	Through Hole
Fuse Type	Board Mount (Cartridge Style Excluded)
Package / Case	Axial
Breaking Capacity @ Rated Voltage	50 A AC, 300 A DC
Operating Temperature Range	-55°C to 125°C

Substitute Part Grouping Explanation

Substitute parts for the MS 4 are selected based on strict electrical and mechanical compatibility criteria. The primary substitution parameters are:

Current Rating: 4 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 / Case: Axial (exact match required)
Operating Temperature Range: -55°C to 125°C (exact match required)

Two substitute parts meet these criteria: 0473004.MRT1L and 0473004.YRT1L, both from Littelfuse Inc. in the PICO® II 473 series. One additional substitute, 0473003.YRT1L, differs in current rating (3 A versus 4 A) and is not electrically equivalent for direct substitution in applications requiring 4 A protection.

Parameter Comparison

Parameter	MS 4 (Bel Fuse)	0473004.MRT1L (Littelfuse)	0473004.YRT1L (Littelfuse)
Current Rating (Amps)	4 A	4 A	4 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
Fuse Type	Board Mount (Cartridge Style Excluded)	Board Mount (Cartridge Style Excluded)	Board Mount (Cartridge Style Excluded)
Package / Case	Axial	Axial	Axial
Breaking Capacity @ Rated Voltage	50 A AC, 300 A DC	50 A	50 A
Operating Temperature	-55°C to 125°C	-55°C to 125°C	-55°C to 125°C
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

For applications currently using the obsolete MS 4, direct substitution is available through either 0473004.MRT1L or 0473004.YRT1L. Both parts are active products from Littelfuse Inc. and provide electrical equivalence across all critical parameters: 4 A current rating, 125 V AC/DC voltage rating, slow blow response, through-hole axial mounting, and identical operating temperature range.

The primary distinction between the two substitute options is REACH compliance status. The 0473004.MRT1L is REACH Unaffected, while 0473004.YRT1L is REACH Affected. Selection between these two should be based on regulatory requirements applicable to the end application and geographic market.

Both substitute parts carry CSA, PSE, and UR approvals, providing regulatory coverage suitable for industrial and consumer applications. The ROHS3 compliance of both substitutes aligns with current environmental standards.

Frequently Asked Questions (FAQ)

Q: Can the 0473003.YRT1L (3 A) be used as a substitute for the MS 4 (4 A)?

A: No. The 0473003.YRT1L is rated for 3 A, which is not electrically equivalent to the 4 A MS 4. Using an undersized fuse creates inadequate circuit protection and violates electrical safety standards.

Q: What is the difference between 0473004.MRT1L and 0473004.YRT1L?

A: Both parts are electrically and mechanically identical with matching current ratings, voltage ratings, response times, and physical dimensions. The primary difference is REACH compliance status: 0473004.MRT1L is REACH Unaffected, while 0473004.YRT1L is REACH Affected. Selection depends on regulatory requirements for your application.

Q: Are the physical dimensions of the substitute parts compatible with the MS 4 footprint?

A: The MS 4 measures 0.125" diameter × 0.280" length. The substitute parts measure 0.135" diameter × 0.280" length. The slight diameter increase (0.010") must be verified against PCB hole tolerances and mechanical clearances in your specific design.

Q: What certifications do the substitute parts carry?

A: Both 0473004.MRT1L and 0473004.YRT1L carry CSA, PSE, and UR approvals. The original MS 4 carried CE, CSA, and cURus approvals. Verify that the substitute certifications meet your application's regulatory requirements.

Q: Are the substitute parts RoHS compliant?

A: Yes. Both 0473004.MRT1L and 0473004.YRT1L are ROHS3 compliant. The original MS 4 RoHS status was not specified in the available data.

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