OPD stands for overcurrent protective device. It is a general classification for any component, such as a fuse or circuit breaker, designed to automatically interrupt electrical power when current exceeds the safe rating of the downstream conductors or equipment. Engineers use this term in specifications and single-line diagrams when the exact type of protection has not yet been selected.
Ensure the upstream OPD is sized to clear a bolted fault within 50 milliseconds.
Related terms
Overcurrent protective device
A component designed to interrupt an electrical circuit when the current exceeds a predetermined safe limit.
Circuit breaker
A mechanical switching device capable of making, carrying and breaking currents under normal and fault conditions.
Fuse
A sacrificial protection device containing a conductive element that melts to safely break a circuit during an overcurrent event.