Varistor protection is RAB-PD-X07-A1, RAB-PD-X08-A1 and RAB-PD-X51-X1 used in the power distribution panels as the 3rd level of overvoltage protection in compliance with appropriate norm, accordingly as a protection placed right in front of the device and eliminating the remnant voltage, which the previous steps of house wiring surge protection failed to break off. The installed surge protection is in form of detachable block, which can discharge the pulse overvoltage and endanger the connected devices to a protective earth conductor. Therefore, it only operates on the so-called three wire distribution system with yellow-green protective conductor. If the overvoltage is really large, the surge protection module would get damaged and the control green light on the module would switch off. The power distribution panel would still be working, however, it would no longer protects against the overvoltage and it is necessary to replace the surge protection module.