Cooper Bussmann FRN-R-40 Cartridge Time Delay Fuse RK5 40A

Product Description

The COOPER BUSSMANN FRN-R-40 is a Class RK5 cartridge-style time delay fuse rated at 40 amps, designed for general-purpose overcurrent protection in industrial, commercial, and HVAC applications. It measures 3 inches (76.2 mm) overall length and 20.6 mm in diameter, making it a standard dual-element cartridge fuse that fits conventional fuse holders. The two-element construction allows it to tolerate motor inrush and startup surges without nuisance tripping while still clearing sustained fault currents. Licensed electricians and HVAC technicians install this fuse when protecting motor loads, disconnect switches, and branch circuit equipment.

This fuse is suited for branch circuit and feeder protection where time delay characteristics are required to ride through motor starting loads. Typical applications include compressor disconnects, air handler units, pump motors, and panel board branch circuits in residential and light commercial systems. The non-indicating body gives no visual blown indication, so a fuse tester or multimeter is the appropriate diagnostic tool during service calls.

Key Features

• Class RK5 time delay rating accommodates motor inrush without nuisance opens
• Dual-element cartridge design for reliable overcurrent and short-circuit protection
• 40-amp continuous current rating for branch circuit and motor load applications
• Non-indicating body — no internal blow indicator
• Fuse holder mount type for standard cartridge fuse blocks and disconnects
• CE Certified, CSA Certified (C22.2 No. 248.12), and UL Listed (248-12 Class RK5)

Compatibility

Designed as a direct-fit replacement for Class RK5 cartridge fuse holders and disconnect blocks that accept a 3-inch by 20.6 mm cartridge fuse at 40 amps. Verify fuse holder ampere and voltage ratings before installation.

Installation Notes

A licensed electrician should perform fuse replacement in accordance with the NEC and any applicable local codes. De-energize and lock out the circuit at the upstream breaker or disconnect before removing or installing the fuse. Use an insulated fuse puller rated for the voltage and current class — never remove a cartridge fuse by hand or with uninsulated tools. Confirm the replacement fuse class, ampere rating, and voltage rating match the original equipment specifications before restoring power.