With the installation of a overvoltage protection device, it acts as a voltage controlled switch and is installed between the active conductors and ground in parallel with the equipment being protected. If the supply voltage is lower than its activation voltage, the protector acts as a high-impedance element preventing current to flow through it. Alternatively, if the supply voltage is higher then the protector acts as an element with an impedance close to zero and thereby preventing it from affecting the receivers. The active part of the system is most commonly a metal oxide varistor (MOV) and it is this that forms the connection between the electric cabling (hot wire) and the ground wire.
