RLD30P400UFF Equivalent & Substitute Parts

Part Overview

The RLD30P400UFF is a polymeric PTC resettable fuse manufactured by Littelfuse Inc., part of the POLY-FUSE® RLD30 series. This component provides overcurrent protection at 30V with a 4A hold current rating in a through-hole radial disc package. The product is currently obsolete, making equivalent substitutes necessary for ongoing system support and component procurement.

Substiute Parts

RLD30P400UFF

Littelfuse Inc.In Stock: 651RLD30P400UFF Datasheet

Current PartRFQ

30R400UF

LittelfuseIn Stock: 477230R400UF Datasheet

DirectRFQ

RUEF400-AP

LittelfuseIn Stock: 1101RUEF400-AP Datasheet

DirectRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the RLD30P400UFF is determined by strict alignment with the following electrical and mechanical parameters:

• Maximum voltage rating of 30V
• Hold current (Ih) of 4A maximum
• Trip current (It) of 8A
• Initial resistance (Ri) minimum of 10 mOhms
• Post-trip resistance (R1) maximum of 50 mOhms
• Operating temperature range of -40°C to 85°C
• Through-hole radial disc package configuration
• Lead spacing compatible with 0.201" (5.10mm) spacing

Both identified substitutes meet these core electrical specifications and physical form factor requirements, ensuring functional equivalence in circuit applications designed for the RLD30P400UFF.

Parameter Comparison

Engineering Selection Recommendations

Both substitute parts are active products from Littelfuse and maintain full electrical and mechanical compatibility with the RLD30P400UFF. Selection between them should be based on the following factors:

30R400UF is the direct successor within the POLY-FUSE® product line, offering the same electrical characteristics and series continuity. This part is available in bulk packaging and represents the primary replacement path for obsolete RLD30 series components.

RUEF400-AP is from the PolySwitch® RUEF series and provides broader regulatory approvals (CQC, CSA, TUV, UL) compared to the RLD30P400UFF (cURus, TUV). This part supports higher maximum current ratings (100A versus 40A) and is supplied in cut tape packaging. The RUEF400-AP is suitable for applications requiring expanded certification scope.

Both parts maintain ROHS3 compliance and identical core protection parameters (30V, 4A hold, 8A trip, 12.7s trip time). Physical dimensions are equivalent within manufacturing tolerances, with lead spacing differences of less than 0.01" (0.05mm).

Frequently Asked Questions (FAQ)

Q: Can 30R400UF and RUEF400-AP be used interchangeably with RLD30P400UFF?

A: Both parts meet the electrical and mechanical specifications required for RLD30P400UFF applications. They share identical voltage, hold current, trip current, resistance characteristics, and operating temperature range. Physical form factors are compatible with standard through-hole radial disc footprints.

Q: What is the difference between the two substitute parts?

A: The primary differences are product series (POLY-FUSE® 30R versus PolySwitch® RUEF), regulatory approvals (30R400UF has cURus/TUV; RUEF400-AP has CQC/CSA/TUV/UL), maximum current rating (40A versus 100A), and packaging format (bulk versus cut tape). Electrical protection characteristics are identical.

Q: Does the height difference between substitute parts affect PCB compatibility?

A: The seated heights vary: RLD30P400UFF at 0.791" (20.10mm), 30R400UF at 0.866" (22.00mm), and RUEF400-AP at 0.760" (19.30mm). These differences are within typical component tolerance ranges for through-hole applications. Verify clearance in your specific PCB assembly if height-constrained space is a design consideration.

Q: Are all three parts ROHS3 compliant?

A: Yes. RLD30P400UFF, 30R400UF, and RUEF400-AP are all ROHS3 compliant, meeting environmental and hazardous substance restrictions.

Q: Which substitute should I select for new designs?

A: For new designs, either active substitute is acceptable. Choose 30R400UF for series continuity within the POLY-FUSE® product family, or RUEF400-AP if your application requires the expanded regulatory certifications (CQC, CSA, UL) or higher maximum current rating capability.

Q: What is the lead spacing tolerance between parts?

A: RLD30P400UFF and 30R400UF both specify 0.201" (5.10mm) lead spacing. RUEF400-AP specifies 0.199" (5.05mm), a difference of 0.002" (0.05mm). This tolerance is within standard PCB footprint design margins for radial through-hole components.