The CEY51A and CEY52A are extended range, three-phase, high-speed, single-zone mho directional-distance relays. These relays include three single-phase units with provision for single phase testing. One target and seal-in unit provides indication of operation for all three distance units and the three-phase contacts are brought out to separate terminal studs.

A CEY53A is a single phase, extended range, zone-one mho distance relay specifically for shunt reactor protection and includes the normal target seal-in unit.
CEY54A is a three-phase, single-zone, phase mho directional distance relay sim-ilar to the 2nd zone CEY52A except the target seal-in connections are modified and the phase contacts are connected in parallel.