The Impact of an Incomplete Overlap of a Copper Conductor and the Corresponding Terminal on the Contact Temperature

By using a specially designed apparatus, the impact of poor contacts caused by an incomplete overlap of a copper conductor and the corresponding terminal of the low-voltage electrical equipment on the contact temperature was tested. The poor contact was simulated using the electrodes of different cross-sectional areas, exposed to different loads. The most frequently used combinations of the contact materials, copper-copper, copper-brass, and copper-stainless steel, were analyzed. The considered percentage of the overlapping areas of the electrodes amounted to 100%, 50%, and 15%. The influence of all of these parameters on the contact temperature, the occurrence of a hot spot, the establishment of a series electric arc, and the contact resistance was analyzed in detail. It was shown that a reduced overlapping area is considerably more dangerous (as a cause of fire) in case of the copper-brass contacts than in case of the copper-copper contacts. However, the most dangerous are the copper-stainless steel connections. (Being the cheapest, the stainless steel terminals can still be found in low-quality sockets.) It was also shown that the copper-brass connections are characterized by the highest contact resistances, which occur when stable electric arcs are established. An example from our practice is presented in order to show the potential consequences of an incomplete overlap.