Compression connectors have been used in overhead wiring systems for the traction system for approximately 30 years for connecting ropes and wires. In this study, hexagonal compression connectors for the catenary have been investigated. Like all current-carrying connections, they are subject to aging as a function of time as well as of the electro-thermal and mechanical load during operation. The diagnosis of the connector's integrity increases the safety and reliability of the entire system, as highly aged connectors can be detected and replaced before a failure occurs. The aim of the investigations is therefore to examine the dominant aging mechanisms and possible test methods to assess the condition of the connections.