Electrical connections are often made up of materials that have various coefficients of thermal expansion. Additionally, the joint materials also carry more current than the bolts, causing the joint to heat up more than the bolts. The resultant differential thermal expansion (DTE) results in an increase in bolt load, which can cause the joint components to yield. During each thermal cycle, bolt load may be reduced. Electrical connections can also loosen over time due to vibration or embedment relaxation, which is caused by microscopic high points on both threads and mating surfaces. As the bolt load is reduced, electrical joint resistance increases or causes heat or hot spots, which can result in even higher resistance and ultimately, catastrophic failure.
- Electrical connections where the components of the connection are made of dissimilar (AL7CU or AL9CU) or similar materials
- Aluminum or copper bus
- Aluminum terminal lug
- Substations / utilities
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