Circuit b for controlling three electrical appliances with a single wire

The circuit for controlling three electrical appliances over a long distance with a single wire is shown in Figure 6-22. It utilizes the unidirectional conductivity of diodes to achieve
control.
    When the transfer switch SA is set to the I, 2, and 3 positions respectively, the contactors KMi, KM2, and KMs are controlled to close, and
the contactors control three electrical appliances.
    Since the AC neutral line (N ) is connected to the ground terminal of the relay through the earth, safety must be paid attention to.