What type of current does a residual current device detect?

A residual current device (RCD) is specifically designed to detect leakage current, which refers to the unintended flow of electrical current that may occur when there is a fault in an electrical system. This leakage typically happens due to insulation failure, moisture, damage to cables, or contact with conductive materials, leading to a risk of electric shock or fire.

The RCD monitors the balance of current flowing in and out of an electrical circuit. Under normal circumstances, the current entering the circuit should equal the current leaving the circuit. If there is a difference, which indicates that some current is leaking to the earth, the RCD will quickly disconnect the supply to prevent harm.

In contrast, while direct current and alternating current are types of electrical flow, they do not define the purpose or function of an RCD. High-frequency current generally refers to signals used in communications and is not related to the protective function of an RCD. Therefore, recognizing that the primary role of an RCD revolves around detecting leakage current is crucial for safety in electrical systems.