The residual current device(RCD) works with no extra power supply to the operating mechanism. It compares the magnitude of the currents through the neutral and phase conductors. The conductors are coiled on toroid and together with the secondary winding form a measurement transformer. The power conductors are coiled in such a way that the magnetic fields generated at electrical current flow through them are mutually neutralized. At failure in the insulation of some of the conductors or at presence of a person under voltage, the system is misbalanced and the magnetic fields can not be neutralized. This residual field generates in the secondary current winding, called current leakage. The device breaks when the value of this current exceeds the limit value of the RCD. Every people from any profession and any cultural level are in close contact with electrical energy at any hour of the day and they may encounter residual currents. Under normal conditions, benefits from electrical energy are countless. However, damages arising from an insulation error are also really huge. Every year, many individuals become victim of electrical accidents. Therefore, use of residual current protection devices has been rendered mandatory in many countries and our country.