MF-R400-AP Equivalent & Substitute Parts

Part Overview

The MF-R400-AP is a polymeric PTC resettable fuse manufactured by Bourns Inc. in the Multifuse® MF-R series. This through-hole radial disc component provides overcurrent protection at 30V with a 4A hold current rating. The part is active in production with full RoHS3 compliance and cURus/TUV approval. Equivalent substitute parts are necessary for supply chain flexibility, alternative sourcing, or when the primary manufacturer part becomes unavailable.

Key Parameters

Parameter	Value
Voltage - Max	30V
Current - Hold (Ih) (Max)	4 A
Current - Trip (It)	8 A
Time to Trip	12.7 s
Resistance - Initial (Ri) (Min)	10 mOhms
Resistance - Post Trip (R1) (Max)	50 mOhms
Operating Temperature	-40°C ~ 85°C
Mounting Type	Through Hole
Package / Case	Radial, Disc
Lead Spacing	0.201" (5.10mm)
Type	Polymeric
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution eligibility for the MF-R400-AP is determined by strict equivalence across the following critical parameters:

Voltage rating: 30V maximum
Current hold (Ih): 4A maximum
Current trip (It): 8A
Time to trip: 12.7 seconds
Resistance initial (Ri): 10 mOhms minimum
Resistance post-trip (R1): 50 mOhms maximum
Operating temperature range: -40°C to 85°C
Mounting configuration: Through hole radial disc
Lead spacing: 0.201" (5.10mm) nominal tolerance

All three substitute parts meet these core electrical and mechanical specifications. Physical dimensions vary within acceptable tolerances for through-hole radial disc packages. Packaging format differences (tape & box versus cut tape) do not affect electrical performance or board-level compatibility.

Parameter Comparison

Parameter	MF-R400-AP (Bourns)	30R400UMR (Littelfuse)	RUEF400-AP (Littelfuse)	RUEF400K-AP (Littelfuse)
Manufacturer	Bourns Inc.	Littelfuse Inc.	Littelfuse	Littelfuse Inc.
Series	Multifuse® MF-R	POLY-FUSE® 30R	PolySwitch® RUEF	PolySwitch® RUEF
Voltage - Max	30V	30V	30V	30V
Current - Hold (Ih) (Max)	4 A	4 A	4 A	4 A
Current - Trip (It)	8 A	8 A	8 A	8 A
Time to Trip	12.7 s	12.7 s	12.7 s	12.7 s
Resistance - Initial (Ri) (Min)	10 mOhms	10 mOhms	10 mOhms	10 mOhms
Resistance - Post Trip (R1) (Max)	50 mOhms	50 mOhms	50 mOhms	50 mOhms
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	Radial, Disc	Radial, Disc	Radial, Disc	Radial, Disc
Lead Spacing	0.201" (5.10mm)	0.201" (5.10mm)	0.199" (5.05mm)	0.199" (5.05mm)
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Active	Active	Active	Active

Engineering Selection Recommendations

All three substitute parts are active production components with full RoHS3 compliance. Selection between MF-R400-AP and its substitutes depends on supply availability and certification requirements specific to the application.

The 30R400UMR (Littelfuse POLY-FUSE® 30R series) maintains identical lead spacing (0.201" / 5.10mm) and is supplied in cut tape format. Approval agencies include cURus and TUV.

The RUEF400-AP and RUEF400K-AP (Littelfuse PolySwitch® RUEF series) feature lead spacing of 0.199" (5.05mm), a 0.02mm tolerance difference from the primary part. Both carry expanded certification coverage including CQC, CSA, TUV, and UL. The RUEF400-AP is supplied in cut tape; the RUEF400K-AP is also supplied in cut tape. Height-seated dimensions differ slightly between variants (0.760" to 0.839") but remain within acceptable through-hole radial disc package tolerances.

Frequently Asked Questions (FAQ)

Q: Can RUEF400-AP or RUEF400K-AP be used as direct replacements for MF-R400-AP on existing PCBs?

A: Yes. The lead spacing difference of 0.02mm (0.199" versus 0.201") is within standard through-hole manufacturing tolerances. All parts are radial disc configuration with identical electrical specifications.

Q: What is the difference between RUEF400-AP and RUEF400K-AP?

A: Both parts are electrically identical with matching electrical specifications. The primary difference is seated height: RUEF400-AP measures 0.760" (19.30mm) while RUEF400K-AP measures 0.839" (21.30mm). Both are acceptable for through-hole applications where component height does not constrain board layout.

Q: Does packaging format affect compatibility?

A: No. The MF-R400-AP is supplied in tape & box format while all substitutes are supplied in cut tape format. Packaging affects logistics and handling only; electrical performance and board-level compatibility remain identical.

Q: Are all parts certified to the same standards?

A: The MF-R400-AP carries cURus and TUV approval. The 30R400UMR carries cURus and TUV approval. The RUEF400-AP and RUEF400K-AP carry CQC, CSA, TUV, and UL approval, providing broader certification coverage for applications requiring expanded agency recognition.

Q: What determines substitution eligibility?

A: Substitution is based on matching voltage rating (30V), current hold (4A), current trip (8A), time to trip (12.7s), initial resistance (10 mOhms minimum), post-trip resistance (50 mOhms maximum), operating temperature range (-40°C to 85°C), and through-hole radial disc package configuration.

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