Ring main switching unit with spur - consists of two on-load isolators which are bridged by off load isolator and is fitted with fuses

摘要

The application is to cable ring mains distribution systems at the point where there is a spur. A compact and relatively less expensive switching unit is produced by bridging the two series connected on-load isolators (3, 4) joining the cable sections (1, 2) with an off-load isolator (8). By this means an expensive circuit breakers in the spur, for example between fuses (6) and transformer (7) can be omitted. As a further simplification the parallel isolator (8) can be hand operated. With the series isolators open and the parallel isolator closed the spur is isolated whilst the ring remains complete. As a refinement the on-load isolators may be fitted with a charged trip mechanism actuated by the spur fuses (6) to trip if a fuse operates.