Final answer:
For a three-phase circuit, three current responsive devices are necessary, with one device per phase for proper operation and monitoring.
Step-by-step explanation:
The question is asking about the number of current responsive devices needed for a three-phase circuit. This relates to how many separate devices or components, such as current transformers or protection relays, would need to be installed to properly monitor or control the current in each phase of a three-phase electrical system.
In a three-phase circuit, you typically need one current responsive device for each phase to ensure balanced operation and accurate monitoring. Therefore, the answer to the question is option (3) 3 current responsive devices required for a three-phase circuit.