The SLA-440-ALE is an electromechanical three-phase voltage monitoring relay used in industrial and commercial electrical systems. It continuously monitors the three incoming phase voltages on a 440 V AC supply to ensure that all three phases are present, in the correct sequence, and within acceptable voltage limits. When the three-phase supply is healthy, the relay’s internal contacts remain energized; if a fault occurs—such as loss of a phase, reversal of phase sequence, or undervoltage—the relay de-energizes and changes its contact state. This change can be used to automatically disconnect power to motors or other equipment, or to trigger alarms and control circuits to protect against damage caused by phase faults.