Sensitive Relay Contact Protection Systems

A protective network for sensitive relay contacts can be expected to extend reliable operation to several million cycles of operation. This result is to be achieved only if the sensitive contact circuit current is limited. Peak current transients on closure are shown to be the critical factor rather than the system voltage as popularly supposed. A 120 volt d-c sensitive contact circuit is considered safer and easier to protect than a comparable 24-volt circuit. It is shown that inductive loads can be successfully protected to values of almost two times that permissible for a resistive load with the type of protective system under consideration. Design procedure is given for a 2-circuit polarized relay protection system estimated to weigh less than eight ounces. It is suggested that available polarized relays when used with the subject protective system will provide power sensitivity, acciracy, and reliability in excess of that available from comparable electronic amplifier equipment.