CSN11-1SPD expensive electronic equipment is being increasingly used in all kinds of business, industy,government and enterprise and domestic households. Electronic discharge, over voltage cause by switching or by lightning often cause there highly sensitive units to fail. Electronic equipment is especially prone up to 1.5km way from lightning strikes due to the electromagnetic fields and cable-bome over voltages. However, effective protection is now available. Over voltage protetive devices for TN-S, TN-C, TN-C-S, TT and IT power system and plants are subdivided into Classes A,B,C and D depending on their application area, accordingly to DIN VDE 0675-6(11.89). Compex offers over voltage protective devices for Classes B to D, witch cover the complete installation on the low volage side.