The 3AF04/3AF05 OVCBs for AC traction power supplies consist of three major parts: the pole assembly, the operating mechanism box, and the supporting steel structure. For easy access, the operating mechanism box is situated inside the supporting steel frame. It features the circuit-breaker operating mechanism including motor, release and auxiliary switches and the control cabinet. The actual switching is carried out by a vacuum interrupter mounted inside the weatherproof pole assembly at electrical potential (live). The two pole assemblies rest on a base frame with a common operating shaft. The pole assemblies consist of two porcelain insulators that separate the terminal connectors from the steel structure. The upper insulator contains the vacuum interrupter: its upper end is fixed to the upper terminal connector, while its lower end allows free axial movement inside flexible connectors to connect it the lower terminal connector. Underneath the lower insulators covers the switching rod is located, which transmits the switching movement from the operating mechanism box to the vacuum interrupter.