A Residual Current Device (RCD) can reduce the likelihood of an electrical injury but a shock can still cause very serious or fatal injuries, so an RCD should only be used as a secondary means of reducing the risk of people being injured by electricity. RCD s are not designed to prevent the ignition of an explosive atmosphere and should not be used for this purpose. The best place for an RCD is built into the main switchboard, as this means that the electrical supply is permanently protected. If this is not possible, an electrical socket outlet incorporating an RCD, or a plug in RCD adaptor, can also provide additional safety. If an electrical socket outlet incorporating an RCD, or a plug in RCD adaptor is used it should be tested, by the user, prior to use by operating the Test button. Faulty RCDs should not be used and either removed for use or labelled as faulty.