ABSTRACT
Additional protection used in the event of failure of basic and fault protection or carelessness by users. Additional protection by residual current device (RCD) is useful back-up to other methods of shock protection. RCD is used as additional protection to the other measures taken, provided that it is rated at 30 mA or less and operating time of not more than 40 ms at test current of five times its operating current. It should be noted that RCD are not the panacea for all electrical ills, they can malfunction, but they are a valid and effective back-up to the other methods. The RCB and RCBO are used as additional protection against shock, it is essential that they operate within set parameters. RCD tester connected by the use of a plug, although flying leads are needed for non-socket outlet circuits, instrument allows a range of out-of-balance currents to flow through the RCD to cause its operation within specified time limits.
