Which detects faults and initiates circuit interruption?

• A. Metering Cubicles
• B. Protection Relay
• C. Area Substation Cubicles
• D. Distribution Transformer

Answer: (B)

The device that detects faults and sends the signal to interrupt current is the protection relay. It continuously monitors electrical quantities such as current and voltage (often via sensors like current and potential transformers) and runs protective logic to spot faults like short circuits or ground faults. When a fault is detected, the relay issues a trip command to the circuit breakers, which then interrupt the faulty current to isolate the problem and protect equipment and personnel.

Metering cubicles are for measuring and recording energy usage, not for fault detection or tripping. Area substation cubicles are enclosures that may house protective equipment and switchgear, but by themselves they don’t perform fault detection. A distribution transformer handles voltage conversion, not fault sensing or interruption. The protection relay is the component that detects faults and initiates the necessary interruption.