RUE185 PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The RUE185 is a polymeric PTC resettable fuse manufactured by Littelfuse Inc. in the PolySwitch® series, rated for 30V maximum voltage with a 1.85A hold current. This component is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement.

PTC resettable fuses provide automatic overcurrent protection by increasing resistance when excessive current flows, then resetting when the fault condition clears. The RUE185 is designed for through-hole radial mounting in disc form factor applications requiring 30V protection at 1.85A hold current levels.

Key Parameters

Parameter	Value
Voltage - Max	30V
Current - Hold (Ih) (Max)	1.85 A
Current - Trip (It)	3.7 A
Resistance - Initial (Ri) (Min)	30 mOhms
Resistance - Post Trip (R1) (Max)	90 mOhms
Time to Trip	8.7 s
Operating Temperature	-40°C ~ 85°C
Mounting Type	Through Hole
Package / Case	Radial, Disc
Lead Spacing	0.201" (5.10mm)

Substitute Part Grouping Explanation

Substitution eligibility for the RUE185 is determined by strict equivalence across the following critical parameters:

Voltage rating: 30V maximum
Hold current (Ih): 1.85A maximum
Trip current (It): 3.7A
Time to trip: 8.7 seconds
Mounting type: Through hole radial disc
Operating temperature range: -40°C to 85°C
Initial resistance and post-trip resistance specifications

Substitute parts are grouped into two categories:

Direct Manufacturer Equivalents maintain identical electrical specifications and physical form factors, differing only in packaging or minor manufacturing variants.

Parametric Equivalents meet all critical electrical parameters but may have minor variations in physical dimensions or resistance tolerances that remain within acceptable substitution limits.

Parameter Comparison

Part Number	Manufacturer	Series	Voltage (Max)	Ih (Max)	It	Ri (Min)	R1 (Max)	Time to Trip	Lead Spacing	Product Status	RoHS Status
RUE185	Littelfuse Inc.	PolySwitch®	30V	1.85 A	3.7 A	30 mOhms	90 mOhms	8.7 s	0.201" (5.10mm)	Obsolete	RoHS non-compliant
RUEF185	Littelfuse Inc.	PolySwitch®, RUEF	30V	1.85 A	3.7 A	30 mOhms	90 mOhms	8.7 s	0.199" (5.05mm)	Active	ROHS3 Compliant
30R185UU	Littelfuse Inc.	POLY-FUSE®, 30R	30V	1.85 A	3.7 A	30 mOhms	90 mOhms	8.7 s	0.201" (5.10mm)	Active	ROHS3 Compliant
0ZRB0185FF1E	Bel Fuse Inc.	0ZRB	30V	1.85 A	3.7 A	30 mOhms	90 mOhms	8.7 s	0.201" (5.10mm)	Active	ROHS3 Compliant
FRU185-30F	RFE/Fuzetec	FRU	30V	1.85 A	3.7 A	30 mOhms	90 mOhms	8.7 s	0.201" (5.10mm)	Active	ROHS3 Compliant
MF-R185	Bourns Inc.	Multifuse®, MF-R	30V	1.85 A	3.7 A	40 mOhms	110 mOhms	8.7 s	0.201" (5.10mm)	Active	ROHS3 Compliant
PTR030V0185-BK	Eaton - Electronics Division	PTR030V	30V	1.85 A	3.7 A	30 mOhms	90 mOhms	8.7 s	0.197" (5.00mm)	Active	RoHS Compliant
PTR030V0185-BK1	Eaton - Electronics Division	PTR030V	30V	1.85 A	3.7 A	30 mOhms	90 mOhms	8.7 s	0.197" (5.00mm)	Active	RoHS Compliant
PFRA.185	SCHURTER Inc.	PFRA	30V	1.85 A	3.7 A	40 mOhms	110 mOhms	8.7 s	0.201" (5.10mm)	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: RUEF185

The RUEF185 is the direct Littelfuse equivalent to the obsolete RUE185. It maintains identical electrical specifications and is manufactured by the original equipment supplier. RUEF185 is ROHS3 compliant and carries active product status with substantial inventory availability (49,657 units). This part is suitable for direct substitution in all applications previously using RUE185.

Secondary Recommendations: 30R185UU, 0ZRB0185FF1E, FRU185-30F

These parts meet all critical electrical parameters and physical mounting requirements. All three are active products with ROHS3 compliance. Selection among these options depends on procurement availability and lead time requirements.

30R185UU: Littelfuse POLY-FUSE® series, identical lead spacing to RUE185
0ZRB0185FF1E: Bel Fuse alternative with AEC-Q200 rating for automotive applications
FRU185-30F: RFE/Fuzetec option with highest inventory availability (1,457 units)

Alternative Options: PTR030V0185-BK, PTR030V0185-BK1

Eaton PTR series parts meet electrical specifications with minor lead spacing variation (0.197" vs. 0.201"). These are suitable where PCB layout accommodates the 0.1mm lead spacing difference. Both carry RoHS compliance and active product status.

Tolerance Consideration: MF-R185, PFRA.185

Bourns MF-R185 and SCHURTER PFRA.185 exhibit higher initial resistance (40 mOhms vs. 30 mOhms) and post-trip resistance (110 mOhms vs. 90 mOhms). These parts are electrically functional equivalents but operate with different resistance characteristics. Selection requires confirmation that circuit design tolerates these resistance variations.

Frequently Asked Questions (FAQ)

Q: Can RUEF185 be used as a direct replacement for RUE185?

A: Yes. RUEF185 is the active production equivalent manufactured by Littelfuse. It maintains identical electrical specifications (30V, 1.85A hold current, 3.7A trip current, 8.7s trip time) and physical form factor. Lead spacing differs by 0.002" (0.05mm), which is negligible for standard PCB layouts.

Q: What is the difference between RUEF185 and 30R185UU?

A: Both are Littelfuse products meeting identical electrical specifications. RUEF185 is the direct RUE185 successor in the PolySwitch® series. 30R185UU is from the POLY-FUSE® series. Both are ROHS3 compliant and active products. Selection depends on procurement preference and availability.

Q: Are MF-R185 and PFRA.185 suitable substitutes?

A: These parts meet the core electrical parameters but exhibit higher resistance tolerances. Initial resistance is 40 mOhms (vs. 30 mOhms) and post-trip resistance is 110 mOhms (vs. 90 mOhms). They are functionally equivalent but operate with different circuit behavior. Use only if circuit design has been verified to tolerate these resistance variations.

Q: What is the significance of lead spacing differences?

A: Lead spacing varies between 0.197" and 0.201" across substitute options. This 0.004" (0.1mm) variation is within standard PCB manufacturing tolerances for through-hole radial components. Verify PCB pad spacing accommodates the selected part number.

Q: Which substitute has the best availability?

A: RUEF185 has the highest inventory (49,657 units). FRU185-30F offers the next best availability (1,457 units). All other options maintain active inventory levels between 1,017 and 15,540 units.

Q: Are all substitutes RoHS compliant?

A: RUEF185, 30R185UU, 0ZRB0185FF1E, FRU185-30F, and PFRA.185 are ROHS3 compliant. PTR030V0185-BK and PTR030V0185-BK1 are RoHS compliant. The original RUE185 is RoHS non-compliant. For new designs, select from ROHS3 compliant options.

Q: Can I use 0ZRB0185FF1E in automotive applications?

A: Yes. 0ZRB0185FF1E carries AEC-Q200 rating, indicating qualification for automotive use. Other substitutes do not carry this specific automotive qualification.

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