Effects of a Reduced Torque on Heating of Electrical Contacts in Plugs and Receptacles

Thermal effects of poor electrical contacts caused by a reduced torque on the wire screw terminal connections in plugs and receptacles were experimentally investigated. By changing the torque, poor connections caused by environmental vibrations or negligence by the installer were simulated. Various types and cross-sectional areas of the copper wires, as well as loads and their duration, were tested. The influence of these parameters on the contact temperature and electrical resistance, the occurrence of a hot spot, and the establishment of a series electric arc were analyzed in detail. It was shown that the poor contact degradation was caused by a constant rise of the contact resistance (caused by a growth of oxides on the contact area). It was also shown that a significant decrease in the contact temperature only slightly influences the contact resistance. However, each repetition of the heating process causes a rise of both the contact resistance and contact temperature. The research results represent an important step in developing a method for detecting poor contacts in low-voltage electrical installations by measuring the earth fault loop impedance.