The WA4 mechanical latching unit for AF09 ... AF96 contactors and NF contactor relays ensures that the contactor or contactor relay remains switched on even if there is a lack or a failure of voltage. Standard contactors can be easily converted into compact latched contactors. The WA4 block contains a mechanical latching device with electromagnetic impulse unlatching (AC or DC) or manual unlatching. Operation After closing, the contactor continues to be held in the closed position by the latching mechanism should the supply voltage fail at the contactor coil terminals. Contactor opening can be controlled: • electrically by an impulse (AC or DC) on the WA4 block coil (the coil is not designed to be permanently energized) • manually by pressing the pushbutton on the front face of the WA4 block. Mounting The WA4 block is clipped onto the front face of the 1-stack contactor where it takes up two slots in central position (see fig. below). The two other slots may accept CA4 single pole auxiliary contacts (1 block on each side of the mechanical latch). Additional CAL4 can be fitted on the side of the contactor in respect to the total number of built-in or additional N.O. and N.C. auxiliary contacts as described in the accessory fitting details part of each contactor type.