Mestek Socket Tester Outlet Tester RCD GFCI NCV Test Outlet checker EU US UK Plug Ground Zero Line 30mA Smart Socket Detector -The polarity detection of the three hole power socket wiring -The protection function detection of the leakage switch -It can quickly and accurately detect the wiring fire protection/laboratory/factory/family Voltage measurement 1. The normal voltage range of zero fire line is plus or minus 10% of the local standard voltage. If it is too high or too low, it may be because the circuit load is too high or the power supply is too low/ too high. 2. The normal voltage of zero-earth wire is le than 2V, if too high maybe it is because there is current leakage, or the three phase-sequence is out of balance or there is signal interference in the circuit. RCD TEST Please turn off all electrical appliances before using this function,and do so with permiion to ensure that the power outage will not cause any harm. The high-definition display can see the screen value clearly in the dark environment