NOTE – A control relay may be a simple relay that translates an external command into a control signal, e.g. a command to close a circuit-breaker, or it may be a more complex device which translates an external command into a number of sequential control signals, e.g. the closing and opening of disconnectors and circuit-breakers to changeover a circuit from one busbar section to another. A control relay may also supervise a characteristic quantity, e.g. voltage, frequency, etc. and produce a control signal which is dependent upon its specific functional design, e.g. under frequency load shedding relay.