RCDs are essential in protecting the people using them, as well as electrical systems and appliances. Regular RCD testing will help electricians identify when an incorrect RCD type has been used. Electricians can complete the testing using the test button on an appliance or fuse box. Alternatively, they can use a loop or RCD tester in a circuit. A correctly functioning RCD will cut power to the appliance or circuit being checked under certain conditions within a particular time. If this does not happen, the electrician can change the RCD, or there could be a fault in the appliance or circuit.