The 2P48 relay is a phase failure relay suitable for 3 phase supplies. The relay is designed to automatically change over from the primary supply to the secondary supply if any phase of the primary supply has faulted. The 2P48 output relay is normally energised and drops out if the phase angle unbalance is greater than the pre-set, an under voltage or reverse phase sequence condition exists. A front panel LED will indicate the faulted phase thus allowing easy recognition of the fault. Each of the incoming phases for both primary and secondary supplies have LED indicators to indicate healthy supplies. The outgoing phases have the same indicators. The LED’s will extinguish for the following conditions excessive negative sequence voltage resulting from phase failure, phase unbalance and reversed phase sequence. A neutral connection must be available for the LED’s to function. Where a neutral is not available the 2P49 version should be used.