The Desco 19224 Ground Hub Monitor, 220VAC, Asian Plug confirms the integrity of the resistance path from the common ground point to electrical ground. It is designed in accordance with ESD TR 12-01 to "monitoring equipment ground connections." When the 19224 is plugged into an AC outlet, the green LED illuminates when both the outlet's wiring is correct and the path to equipment ground via the equipment grounding conductor is intact. The monitor provides 12 verified ground points when in PASS condition. The red LED illuminates when either the outlet's wiring is incorrect or the path to equipment ground is defective. The outlet ground line is tested by measuring voltage between it and the neutral line. It is normal to have a few volts of AC induced on the neutral line. If the Ground Hub Continuous Monitor measures only a few volts, the ground line to neutral impedance is low and the ground line would make a suitable ESD ground point. If the monitor measures more than just a few volts between ground and neutral, this indicates either that they are not referenced to each other or that the outlet and associated wiring should be checked for loose connections. In this case, the Ground Hub Continuous Monitor will sound a warning alarm and display a red FAIL indication and should not be used for an ESD grounding point until corrected.