What safety device is designed to cut off electrical flow when a fault is detected?

The Residual Current Device (RCD) is specifically designed to enhance electrical safety by monitoring the electrical current flowing through a circuit. When it detects an imbalance—indicating that current is leaking to the ground, which could be due to a fault in the wiring or an appliance—it promptly disconnects the electrical supply. This quick disconnection helps prevent electric shocks, fires, and other electrical hazards by ensuring that potentially dangerous electrical conditions are resolved before they escalate.

In contrast, other options serve different functions. A fuse is a safety device that protects electrical circuits by melting and breaking a circuit if the current exceeds a certain threshold, but it doesn't actively monitor for ground faults like the RCD does. A transformer is used to change the voltage level in an electrical circuit, and a capacitor stores electrical energy for later use, neither of which are designed for safety cut-offs in fault detection scenarios. Therefore, the RCD's specialized function of monitoring and disconnecting in case of faults makes it the correct choice for this question.