Before a current transformer is returned to service, what must field personnel verify?

Before a current transformer (CT) is returned to service, it is crucial for field personnel to verify that the CT secondary is not open-circuited. An open-circuit condition in the secondary of a current transformer can lead to dangerously high voltage levels, which poses significant safety risks and can damage the CT itself. When the secondary is left open, the magnetic circuit is disrupted, causing the current in the primary to create an induced voltage that can exceed the design limits of the CT. This can harm both personnel and equipment.

By confirming that the secondary is not open-circuited, field personnel help ensure safe operation and longevity of the current transformer, allowing the system to operate as intended without the risk of electrical hazards. Proper grounding and preventing overload are also important considerations, but the immediate danger posed by an open-circuit condition makes this verification critical before re-energizing the circuit.