In one of the industrial site, the no earthed system has been chosen in electrical designing stage. Therefore nobody anticipated a strong earth fault current in the system. On the other hand, the primary earthing system was not installed very well and related standards recommendations weren't applied in the erection stage; because the related engineers thought that the primary earthing was not very important in” no earthed systems” and they could ignor its erection in some area. Many years after start up and operation of plant , some cable insulations were damaged due to no suitable operation conditions. One day a short circuit happened between one old cable and related electromotor casing. Unlike anybody imagined, a sever short circuit current passed through electrical system and ground surface which could be very dangerous for anybody in site area. How can you explain the reason of that accident?