The Ermenrich Zing ST30 Socket Tester is designed to test whether all of the sockets are properly wired and to check the voltage. The tester must be plugged directly into a socket, and the LED’s flashing will indicate various electrical faults: no ground/no neutral, live/neutral reverse, or live/ground reverse. In addition, the specific color code that appears on the tester screen signals the correct wiring condition. The function of each code is written on the device.