Equivalent & Substitute Parts for 72R040XU

Part Overview

The 72R040XU is a polymeric PTC resettable fuse manufactured by Littelfuse, part of the POLY-FUSE® 72R series. This through-hole radial disc component is rated for 72V maximum voltage with a 400 mA hold current and 800 mA trip current. The product is currently obsolete, making identification of equivalent and substitute parts essential for ongoing system maintenance and component sourcing.

Key Parameters

Parameter	Value
Voltage - Max	72V
Current - Hold (Ih) (Max)	400 mA
Current - Trip (It)	800 mA
Current - Max	40 A
Resistance - Initial (Ri) (Min)	550 mOhms
Resistance - Post Trip (R1) (Max)	1.29 Ohms
Operating Temperature	-40°C ~ 85°C
Mounting Type	Through Hole
Package / Case	Radial, Disc
Type	Polymeric

Substitute Part Grouping Explanation

Substitution for the 72R040XU is determined by strict equivalence across the following critical parameters:

Voltage rating: 72V maximum
Hold current (Ih): 400 mA maximum
Trip current (It): 800 mA
Mounting configuration: Through hole radial disc
Polymeric PTC resettable fuse type
Operating temperature range: -40°C to 85°C
Post-trip resistance: 1.29 Ohms maximum

All identified substitute parts maintain these electrical and mechanical specifications within the tolerances provided. Dimensional variations within the radial disc package category are acceptable provided lead spacing and mounting compatibility are preserved.

Parameter Comparison

Parameter	72R040XU (Littelfuse)	RXEF040S (Littelfuse)	RXEF040 (Littelfuse)	MF-RX040/72-0 (Bourns)
Voltage - Max	72V	72V	72V	72V
Current - Hold (Ih) (Max)	400 mA	400 mA	400 mA	400 mA
Current - Trip (It)	800 mA	800 mA	800 mA	800 mA
Current - Max	40 A	40 A	40 A	40 A
Resistance - Initial (Ri) (Min)	550 mOhms	550 mOhms	550 mOhms	520 mOhms
Resistance - Post Trip (R1) (Max)	1.29 Ohms	1.29 Ohms	1.29 Ohms	1.29 Ohms
Time to Trip	3.8 s	3.8 s	3.8 s	3.9 s
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
Type	Polymeric	Polymeric	Polymeric	Polymeric
Product Status	Obsolete	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

RXEF040 (Littelfuse) is the primary recommended substitute. This part maintains active product status with full electrical and mechanical equivalence to the 72R040XU. Approval agencies include CQC, CSA, TUV, and UL, providing comprehensive regulatory coverage. REACH status is unaffected, confirming compliance with environmental regulations.

RXEF040S (Littelfuse) serves as a secondary option with identical electrical specifications and active status. This variant is packaged in bag format and carries equivalent certifications (CQC, CSA, TUV, UL).

MF-RX040/72-0 (Bourns) is an alternative from a different manufacturer. Initial resistance is 520 mOhms (within tolerance of the 550 mOhms minimum specification), and time to trip is 3.9 seconds versus 3.8 seconds for the original part. All other parameters match exactly. This part carries cURus and TUV approvals and maintains ROHS3 compliance.

All three substitute parts are currently in stock with adequate inventory levels for production and replacement applications.

Frequently Asked Questions (FAQ)

Q: Can RXEF040 directly replace 72R040XU in existing designs?

A: Yes. RXEF040 maintains electrical equivalence across all critical parameters: 72V voltage rating, 400 mA hold current, 800 mA trip current, and identical post-trip resistance. Through-hole radial disc mounting is identical. Lead spacing (0.199" / 5.05mm) is compatible with standard PCB layouts designed for the original part.

Q: What is the difference between RXEF040 and RXEF040S?

A: Both parts are electrically identical with matching voltage, current, and resistance specifications. The primary difference is packaging: RXEF040S is supplied in bag format, while RXEF040 is supplied in bag format as well. Both are active products from Littelfuse with equivalent certifications.

Q: Is MF-RX040/72-0 from Bourns a suitable alternative?

A: Yes. MF-RX040/72-0 meets all electrical requirements with 72V rating, 400 mA hold current, and 800 mA trip current. Initial resistance is 520 mOhms, which is within acceptable tolerance. Time to trip is 3.9 seconds compared to 3.8 seconds for the original, representing a negligible difference in circuit protection response. Dimensional variations are minor and compatible with standard through-hole radial disc PCB footprints.

Q: Are all substitute parts RoHS compliant?

A: Yes. All three substitute parts (RXEF040, RXEF040S, and MF-RX040/72-0) are ROHS3 compliant, meeting current environmental and regulatory requirements.

Q: What certifications apply to these substitute parts?

A: RXEF040 and RXEF040S carry CQC, CSA, TUV, and UL approvals. MF-RX040/72-0 carries cURus and TUV approvals. Both certification sets provide comprehensive regulatory coverage for industrial and commercial applications.

Q: Can these parts be used interchangeably in the same circuit?

A: Yes. All substitute parts maintain the same electrical performance envelope and mounting configuration. Circuit behavior will be functionally identical within the specified operating parameters.

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