High voltage ring main unit is generally divided into three types: air insulation, solid insulation, and SF6 insulation. It is used for switching load current, breaking short-circuit current, transformer no-load current, charging current of overhead lines and cable lines at a certain distance, and plays a control and protection role. It is an important switch equipment for ring network power supply and terminal power supply.

In the cabinet, the load switches equipped with air insulation mainly include gas production type, pressure type, and vacuum type. The load switches equipped with SF6 insulation are SF6 type. Due to the SF6 gas being enclosed in the shell, the partition formed by it is not visible.

The load switch in the ring main unit generally requires three positions, namely cutting off the load, isolating the circuit, and possibly relying on grounding. Gas producing, compressed, and SF6 load switches are easy to achieve three positions, while vacuum arc extinguishing switches can only be disconnected and cannot be isolated. Therefore, in general, a vacuum load ring main switch cabinet is equipped with an isolation switch in front of the load switch to form an isolation break.