The electrical system of our homes is one-phase, that is, it is by using two electric cables plus the messmeter cable.
To locate the phase cable and the neutral cable we must open a socket box so that you can tap the power cord with the instrument.
The one fixed at the center of the grip (often yellow stripped of green) is the cable of the messaterra and if tested with the lookup phase should never turn on the bulb of the lookup phase, if this happens it would mean that there was some error in the realization of the plant and you will need to remedy it as soon as possible.
One of the other two cables will have to turn on the phase (phase cable) and the other no (neutral cable).
