UK PLUG IN ELECTRICAL SOCKET TESTER Easy plug-in operation 3 Light indicators The other indicator sequences warning of specific faults such as No Earth or Live and Neutral reversed, etc. Simply plug into any normal mains socket to test, all three indicators will light up if all is OK. Mains Socket Tester allows you to instantly check your 13 Amp Household mains sockets installations and features clear instructions on the face of the unit for a quick confirmation of the socket status.