An earth ground connection of the exposed conductive parts of electrical equipment helps protect from electric shock by keeping the exposed conductive surface of connected devices close to earth potential, when a failure of electrical insulation occurs. When a fault occurs, current flows from the power system to earth. To protect equipment as well severe electric shock due to heavy leakage, special devices like residual breakers or outlets which detects the fault at very low leakage level and interrupts the circuit as soon as fault initiate. Although over current protection, fuse or circuit breaker are available in circuits for complete isolation of power, but their operating level is too high. To ensure the voltage on exposed surfaces is not too high, the impedance (resistance) of the connection to earth must be kept low relative to the normal circuit impedance.