What does an RCD (Residual Current Device) do?

An RCD, or Residual Current Device, functions as a critical safety device in electrical systems by detecting imbalances in electrical current. When it identifies that the current flowing through a live conductor does not match the current returning through the neutral conductor—indicative of a leakage current—this device quickly disconnects the power supply. This mechanism is vital for preventing electric shocks, which can occur if a person comes into contact with a live conductor while grounded, thus posing a serious safety risk.

The other options describe functions that are outside the capabilities of an RCD. For example, limiting current flow is a function typically associated with circuit breakers or fuses, while voltage regulation is managed by devices such as voltage regulators or transformers. Providing backup power during outages is a function of uninterruptible power supplies (UPS) or generators, rather than an RCD. Hence, the primary and unique role of an RCD is to enhance electrical safety by detecting and responding to ground faults, mitigating the risk of electric shock.