Littelfuse RUE400 PTC Resettable Fuse 30V 4A Equivalent & Substitute Parts

Part Overview

The Littelfuse RUE400 is a polymeric PTC resettable fuse rated for 30V maximum voltage and 4A hold current (Ih), designed for through-hole radial mounting in disc configuration. This component is classified as obsolete, making equivalent substitute parts necessary for ongoing design support and procurement. PTC resettable fuses provide automatic overcurrent protection by increasing resistance when current exceeds trip threshold, then resetting when the fault condition clears.

Key Parameters

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

Substitute Part Grouping Explanation

Substitution eligibility for the RUE400 is determined by strict electrical and mechanical parameter matching:

Electrical Criteria (Mandatory):

Voltage rating: 30V maximum
Hold current (Ih): 4A maximum
Trip current (It): 8A
Time to trip: 12.7 seconds
Initial resistance (Ri): 10 mOhms minimum
Post-trip resistance (R1): 50 mOhms maximum
Operating temperature: -40°C to 85°C

Mechanical Criteria (Mandatory):

Mounting type: Through hole
Package configuration: Radial, disc
Lead spacing: 0.201" (5.10mm) nominal tolerance

All substitute parts listed meet these core parameters. Variations in seated height, length, and width remain within acceptable mechanical tolerances for through-hole radial disc components and do not affect electrical performance or circuit board compatibility.

Parameter Comparison

Part Number	Manufacturer	Voltage (Max)	Ih (Max)	It	Ri (Min)	R1 (Max)	Temp Range	Lead Spacing	Product Status	RoHS Status
RUE400	Littelfuse	30V	4A	8A	10 mOhms	50 mOhms	-40°C to 85°C	0.201" (5.10mm)	Obsolete	RoHS non-compliant
RUEF400	Littelfuse	30V	4A	8A	10 mOhms	50 mOhms	-40°C to 85°C	0.199" (5.05mm)	Active	RoHS3 Compliant
30R400UF	Littelfuse	30V	4A	8A	10 mOhms	50 mOhms	-40°C to 85°C	0.201" (5.10mm)	Active	RoHS3 Compliant
FRU400-30F	RFE/Fuzetec	30V	4A	8A	10 mOhms	50 mOhms	-40°C to 85°C	0.201" (5.10mm)	Active	RoHS3 Compliant
MF-R400	Bourns Inc.	30V	4A	8A	10 mOhms	50 mOhms	-40°C to 85°C	0.201" (5.10mm)	Active	RoHS3 Compliant
PTR030V0400-BK	Eaton - Electronics Division	30V	4A	8A	10 mOhms	50 mOhms	-40°C to 85°C	0.197" (5.00mm)	Active	RoHS Compliant
RS30-400	OptiFuse	30V	4A	8A	10 mOhms	50 mOhms	-40°C to 85°C	0.201" (5.10mm)	Active	RoHS3 Compliant
PFRA.400	SCHURTER Inc.	30V	4A	8A	10 mOhms	50 mOhms	-40°C to 85°C	0.201" (5.10mm)	Active	RoHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: RUEF400 (Littelfuse)

The RUEF400 is the direct Littelfuse equivalent with active product status and RoHS3 compliance. As a manufacturer-direct substitute from the same OEM, it provides design continuity and supply chain reliability. Lead spacing tolerance (0.199" vs. 0.201") is within acceptable mechanical variation for through-hole radial components.

Secondary Recommendations:

30R400UF (Littelfuse POLY-FUSE® series) and PFRA.400 (SCHURTER) maintain exact lead spacing (0.201") and offer active status with full RoHS3 compliance. Both are suitable for direct substitution with no circuit board layout modification required.

Alternative Suppliers:

FRU400-30F (RFE/Fuzetec), MF-R400 (Bourns), RS30-400 (OptiFuse), and PTR030V0400-BK (Eaton) all meet electrical specifications and hold active product status. These options provide supply diversification and are electrically interchangeable. Lead spacing variations (0.197" to 0.201") remain within standard PCB tolerance for radial through-hole mounting.

Compliance Consideration:

All substitute parts listed are RoHS3 compliant or RoHS compliant, addressing environmental regulatory requirements that the obsolete RUE400 does not meet.

Frequently Asked Questions (FAQ)

Q: Can I use any of these substitute parts as a direct replacement for RUE400?

A: Yes. All listed parts meet the core electrical parameters (30V, 4A Ih, 8A It, 12.7s trip time) and mechanical requirements (through-hole radial disc, 5.0-5.1mm lead spacing). No circuit modifications are required.

Q: What is the difference between these substitute parts?

A: All parts are electrically identical. Differences exist only in physical dimensions (seated height, length, width) and manufacturer. These dimensional variations do not affect electrical performance or standard PCB compatibility for radial through-hole mounting.

Q: Why should I choose RUEF400 over other options?

A: RUEF400 is the direct Littelfuse equivalent, providing design continuity with the original RUE400. It maintains the same manufacturer support, documentation, and supply chain as the original component.

Q: Are there any lead spacing concerns with these substitutes?

A: Lead spacing across all parts ranges from 0.197" to 0.201" (5.00mm to 5.10mm). This variation is within standard PCB tolerance for radial through-hole components and does not require board redesign.

Q: What is the significance of RoHS3 compliance?

A: RoHS3 compliance indicates the part meets current environmental and hazardous substance restrictions. The obsolete RUE400 is RoHS non-compliant. All active substitute parts are RoHS3 or RoHS compliant, meeting modern regulatory requirements.

Q: Can I mix different substitute parts in the same design?

A: Yes. All parts are electrically and mechanically equivalent. Mixing manufacturers or part numbers in the same circuit presents no technical issue, though single-source procurement is recommended for supply chain consistency.

Q: What is the current-max specification, and why do some parts differ?

A: Current-max (40A or 100A) represents the maximum current the fuse can handle before permanent damage. This does not affect substitution eligibility, as the hold current (Ih = 4A) and trip current (It = 8A) remain constant across all parts.

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