Under the 50 Hz AC operating voltage there is a AC current inside the MOA. For a serviceable MOA, it is about 0.5 mA (some models can have up to 1 mA). If the current increases, then this is the basis for checking the MOA – this is the reasoning of those who lobby for the measurement of the MOA conductivity current under operating voltage. However, in fact, this is useless, since not only the specified current passes through the grounding circuit of the MOA, but also the second one – the insulation leakage current passing through the outer surface of the MOA. This second current can be up to 10 mA for the absolutely operable MOA, and this current depends on the time of day, air humidity, the degree of contamination of the outside surface of the MOA. Thus, the personnel who sees the change in the readings of the device, never knows what they are connected with – with changes inside the MOA (that is dangerous) or with the current on the surface of the MOA (no danger at all). Or maybe the change of the device’s current is due to fluctuations in the AC operating voltage of the network. That is, you get information that you don’t understand what to do with.