Transistor switch by ETI with nominal voltage 400V. When the power of the electrical energy network is unstable or interrupted, a transistor switch allows the supply of power from a backup power source, such as a generator, automatically or manually, ensuring continuous and safe power supply. The number of poles of a panel switch corresponds to the number of circuits it can control. Thus, a monopole switch can control the power supply to one circuit, a bipole to two, etc.