Abstract: The harmful effects on optical cable and wire cable, caused by direct stroke lightning is described. It deals with the method for calculating these effects. Gives the formula of determing the minium lightning current to make breakdown of the insulation between the cable metallic sheath and the wire core. Finally it gives also the formula for calculating the protection effectiveness of lighting protection wire.

Key words: electromagnetic theory, direct-stroke lightning, induced voltage, polarization plane rotation, lightning-protection wire