Equivalent & Substitute Parts for MF-S420S

Part Overview

The MF-S420S is a polymeric PTC resettable fuse manufactured by Bourns Inc. in the Multifuse® MF-S series, rated for 30V maximum voltage with a 4.2A hold current. This component is classified as obsolete, necessitating identification of active equivalent and substitute parts for ongoing design requirements and procurement needs.

Key Parameters

Parameter	MF-S420S Value
Voltage - Max	30V
Current - Hold (Ih) (Max)	4.2 A
Current - Trip (It)	7.6 A
Current - Max	100 A
Time to Trip	6 s
Resistance - Initial (Ri) (Min)	12 mOhms
Resistance - Post Trip (R1) (Max)	40 mOhms
Operating Temperature	-40°C ~ 85°C
Package / Case	Strap
Size / Dimension	1.240" L x 0.522" W (31.50mm x 13.25mm)
Thickness (Max)	0.043" (1.10mm)
Type	Polymeric
RoHS Status	ROHS3 Compliant
Approval Agency	cURus, TUV

Substitute Part Grouping Explanation

Substitution eligibility for the MF-S420S is determined by the following critical parameters:

Voltage rating (30V maximum)
Current hold rating (4.2A)
Current trip rating (7.6A)
Package type (Strap configuration)
Physical dimensions (1.240" L x 0.522" W)
Operating temperature range (-40°C ~ 85°C)
Polymeric PTC resettable fuse technology

Substitute parts are classified into two categories:

Direct Equivalents: Parts with identical electrical specifications (voltage, hold current, trip current, resistance values) and physical dimensions, differing only in manufacturer or product status.

Similar Equivalents: Parts with the same voltage rating and package type but with different hold current ratings (4.6A vs 4.2A), suitable for applications with lower current requirements.

Parameter Comparison

Parameter	MF-S420S (Bourns)	MF-S420 (Bourns)	SRP420F (Littelfuse)	0ZSA0420FF1E (Bel Fuse)	SRP350F (Littelfuse)
Manufacturer	Bourns Inc.	Bourns Inc.	Littelfuse	Bel Fuse Inc.	Littelfuse Inc.
Product Status	Obsolete	Active	Active	Active	Active
Series	Multifuse® MF-S	Multifuse® MF-S	PolySwitch® SRP	0ZSA	PolySwitch® SRP
Voltage - Max	30V	30V	30V	30V	30V
Current - Hold (Ih) (Max)	4.2 A	4.2 A	4.2 A	4.2 A	4.6 A
Current - Trip (It)	7.6 A	7.6 A	7.6 A	7.6 A	6.3 A
Current - Max	100 A	100 A	100 A	100 A	100 A
Time to Trip	6 s	6 s	6 s	6 s	3 s
Resistance - Initial (Ri) (Min)	12 mOhms	12 mOhms	12 mOhms	12 mOhms	17 mOhms
Resistance - Post Trip (R1) (Max)	40 mOhms	40 mOhms	40 mOhms	40 mOhms	50 mOhms
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Package / Case	Strap	Strap	Strap	Strap	Strap
Size / Dimension	1.240" L x 0.522" W (31.50mm x 13.25mm)	1.240" L x 0.522" W (31.50mm x 13.25mm)	1.240" L x 0.522" W (31.50mm x 13.25mm)	1.240" L x 0.522" W (31.50mm x 13.25mm)	1.185" L x 0.522" W (30.10mm x 13.25mm)
Thickness (Max)	0.043" (1.10mm)	0.043" (1.10mm)	0.043" (1.10mm)	0.043" (1.10mm)	0.043" (1.10mm)
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Approval Agency	cURus, TUV	cURus, TUV	CSA, TUV, UL	cURus, TUV	CSA, TUV, UL

Engineering Selection Recommendations

Primary Recommendation - Direct Equivalents:

MF-S420, SRP420F, and 0ZSA0420FF1E are direct parametric equivalents to the obsolete MF-S420S. All three parts maintain identical electrical specifications: 30V voltage rating, 4.2A hold current, 7.6A trip current, 6-second trip time, and 12mOhms initial resistance. All are active products with ROHS3 compliance.

MF-S420 (Bourns) provides continuity within the same manufacturer series and maintains identical certifications (cURus, TUV). SRP420F (Littelfuse) and 0ZSA0420FF1E (Bel Fuse) offer equivalent performance with expanded certification coverage (CSA, TUV, UL for SRP420F).

Secondary Recommendation - Similar Equivalent:

SRP350F (Littelfuse) is a similar equivalent suitable for applications where a lower hold current rating (4.6A vs 4.2A) is acceptable. This part maintains the 30V voltage rating, strap package configuration, and operating temperature range. The trip current is 6.3A with a faster 3-second trip time. Physical dimensions differ slightly (1.185" L vs 1.240" L). This substitution is appropriate only when circuit design permits the reduced current hold specification.

All substitute parts are active products with current inventory availability and ROHS3 compliance status.

Frequently Asked Questions (FAQ)

Q: Can MF-S420 be used as a direct replacement for MF-S420S?

A: Yes. MF-S420 is a direct equivalent with identical electrical parameters (30V, 4.2A hold, 7.6A trip, 6s trip time) and physical dimensions. The primary difference is product status: MF-S420S is obsolete while MF-S420 is active. Both are Bourns Multifuse® series components with cURus and TUV certifications.

Q: What is the difference between SRP420F and 0ZSA0420FF1E?

A: Both are direct parametric equivalents to MF-S420S with identical electrical specifications and physical dimensions. SRP420F is manufactured by Littelfuse (PolySwitch® series) with CSA, TUV, and UL certifications. 0ZSA0420FF1E is manufactured by Bel Fuse Inc. (0ZSA series) with cURus and TUV certifications. Selection depends on certification requirements and supply chain preferences.

Q: When should SRP350F be considered instead of the direct equivalents?

A: SRP350F should be selected only when circuit design specifications permit a lower hold current rating (4.6A vs 4.2A). This part features a faster trip time (3 seconds vs 6 seconds) and slightly different physical dimensions (1.185" L vs 1.240" L). Electrical compatibility must be confirmed before substitution.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. MF-S420, SRP420F, 0ZSA0420FF1E, and SRP350F are all ROHS3 compliant with moisture sensitivity level 1 (unlimited).

Q: What certifications apply to each substitute part?

A: MF-S420 and 0ZSA0420FF1E carry cURus and TUV certifications. SRP420F and SRP350F carry CSA, TUV, and UL certifications. Application requirements may dictate which certification set is necessary.

Q: Do the substitute parts have the same strap package configuration?

A: Yes. All substitute parts use strap package configuration. Physical dimensions are identical for MF-S420, SRP420F, and 0ZSA0420FF1E (1.240" L x 0.522" W). SRP350F has slightly different length (1.185" L) but maintains the same width (0.522" W) and thickness (0.043").

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