Mechanics of Bolted Electrical Splices

Localized heating of bolted electrical splices in the power distributing bus is a primary concern in the industrial automation industry. While localized heat generation problems are commonly reported in the field, it is not entirely clear what the root causes are. A methodology is presented for development of a tool to measure in-situ the influence of clamping load on the thermo-electric behavior of the splice joint. Applied research and reasoning used to identify probable root causes for failures reported in the field are also presented. Experiments were conducted to characterize the mechanical properties of the bolt and nut system used in service. A bolt was modified and retrofitted with strain gauges. This system was calibrated as a load cell and experiments were conducted to develop a sample specific model for determining the bolt pretension as a function of torque applied to the nut. The methods herein described can be implemented for applications in which optimal performance of bolted connections is required. Measurements were made of the electrical contact resistance and an idealized finite elements simulation of the contacting bus materials was studied alongside real samples. Based on this study, the author presents potential root causes for the onset of problematic localized heat generation