Electrical Inspection, Testing and Certification Practice Exam 2025 – Comprehensive All-in-One Guide for Exam Success!

The maximum permitted disconnection time for a 100mA Residual Current Device (RCD) is 300 milliseconds. This standard is in place to ensure the safety of individuals when there is a fault in the electrical system. RCDs are designed to quickly disconnect the supply of electrical power when they detect an imbalance between the live and neutral currents, which may indicate a leakage current to earth.

The 300-millisecond disconnection time is particularly important in reducing the risk of electric shock. In the event that a person inadvertently comes into contact with a live conductor, a rapid disconnection can prevent serious injury or even fatality. The set limit of 300 milliseconds has been established based on research and safety testing which indicates that quick power interruption significantly minimizes injury.

Understanding this time frame helps anyone involved in electrical inspections, installations, or safety compliance recognize the requirements for RCDs and the importance of ensuring that these devices operate within the stipulated parameters to protect human life and comply with regulatory standards.