Certain socket outlet testers are provided with misleading reassurances and can be positively dangerous. Simple socket outlet testers have become very popular with electricians but most of them are not suitable as the only method of checking whether a socket outlet is safe. They may show that the socket is functional but that does not meet all of the requirements of BS 7671.
This warning follows a report by the Health & Safety Executive which shows many electricians are using these testers as the only method of verifying the safety of a socket. Simple outlet testers will not warn the user when neutral and protective conductors are transposed, nor will they show when earth fault loop impedances are excessive. The situation isn’t helped by manufacturers that make false or misleading claims in their adverts and user instructions. The only safe approach is to use the appropriate individual instruments or the more advanced socket outlet testers that also detect and display various bands of earth fault loop impedance.
BS 7671 requires that new, repositioned or repaired socket outlets are not put into service until the required verification procedures have been completed. These procedures include continuity testing of protective conductors and ring final circuit conductors, measurement of insulation resistance, checking of polarity and measurement of earth fault loop impedance.