How do you test a residual current device?

Testing a residual current device (RCD) is primarily done by pressing the test button to simulate a fault condition. This button is designed to create an imbalance in the current flow, which the RCD detects. When the button is pressed, it essentially mimics a potential earth fault, causing the RCD to trip if it is functioning correctly. This ensures that the device can effectively respond in real-world situations where there is a fault, thereby providing the necessary electrical safety to prevent electric shock or fire hazards.

The other options involve methods that do not specifically test the operational effectiveness of the RCD. While checking physical connections and disconnecting the power supply are important for installation and overall safety checks, they do not assess the device's functionality in terms of fault detection. Setting the RCD to maximum voltage does not apply as it does not provide an indication of the device's performance in detecting imbalances in current flow. Therefore, the correct and most effective method to ensure an RCD is working properly is by using its test button.