Answer: Surge is an over voltage which sudden occurs to the electrical system caused by the induced of various conditions such as lightning, cut or short-circuit of the AC power system, open – close of a large AC power consumption equipments and etc., by induced into the electrical power line, such as the AC 220 Volt 50 Hz. single phase or the 380/220 Volt 50 Hz. three phase four wires as well as induced into signal lines such as telephone / leased lines and etc., which can cause the various devices (Loads) to damages.

The Surge can be classified into two different types as follows :

1. Transient, which is condition of the over voltage that sudden occurs in a short period of time such as one-million of a second.

2. Temporary Over Voltages (TOVs), which is the condition of the over voltage that sudden occurs but the duration not longer than 3 seconds (Less than a few seconds).