The EFU50 part of the extensive OPTIMA range of earth fault protection relays (RCD's), represents a major breakthrough in RCD technology, since it will detect residual direct current without having to use Hall Effect transducers. It can also be installed to detect when and where an earth fault occurs in a DC wired circuit, thus eliminating costly man hours and down-time in locating system faults.

The EFU50 is designed to react to DC current only and will reject induced or stray alternating current from 25Hz to 250Hz up to 2 Amps whilst still operating precisely on DC residual current against its preset level. This enables the EFU50 to be used to detect imposed DC current on AC circuits as well as its primary use of DC residual current detection.