The 3 phase 4 wire voltage relays are designed for applications where the three phases need to be individually monitored for under voltage against neutral and correct phase sequence. The PNDA and PNDI contain a standard timing function. In addition the PNDI offers a true time delay on drop out even at total power failure. The relay works in "fail safe" mode and need no external power supply.
Operation
Under normal phase conditions the relay is energized - contacts 11-14 and 21-24 closed - and the green "input" LED and the yellow "relay" LED are switched on. If one or more phase voltages are below the preset under voltage value, the red "input" LED will be switched on and stay on until all three phase voltages are above the set value plus the preset differential, given by a percentage of the under voltage offset from the nominal value. If the state of the relay is not corresponding to the input signal, the yellow LED indicating delay "ON" or "OFF" will be on until the relay changes state and corresponds to the input. In case of wrong phase sequence the relay will not be energized and the red "inversed phase sequence" LED will be on indicating the fault.
