The electric power is something that is very important and widely used in supporting human life, but the power is also very dangerous to human safety itself. Low voltage 220 V is part of the electric power distribution system. On this channel it is possible short circuit due to installation errors. Disturbances in this system becomes a possibility of being harmful to humans, because the electric current can make men swoon even death. So that people can avoid the danger that occurs, then the system installation households should be connected to the ground through a prisoner whose price is relatively low. Of the prisoners is to be investigated in the installation of existing homes in the city of Medan.