The Nepean HLO Holistic Earth Fault Lock Out relay has been designed to detect Earth Faults on conductors in an outgoing circuit of an electrical system and to prevent the closure of the electrical supply to the de-energised circuit.

When incoming mains power is switched onto the system the HLO scans the outgoing cable and will lockout if an earth fault is present of 1M ohms or less. Detection of a fault will prevent the circuit switching device from being closed.

The unit is failsafe in operation and will drop out on detection of a fault and remain open until the fault is cleared. The power supply to this unit is designed to maintain the function in its healthy mode for 2 seconds under no volt conditions thus preventing premature drop out under system fault conditions.