When working on apparatus, such as circuit breakers, it is necessary to disconnect the
apparatus from the live system and to apply visual earths. For this purpose isolators and
earthing switches are provided. Isolators differ from circuit breakers in that they should only
rotating type of isolator.
Fuses are mainly used at voltages up to 22 kV. High rupturing capacity (h.r.c.) fuse
elements are used. The fuses are often pole-mounted as drop-out fuse link assemblies. A
typical arrangement is shown in Fig. 1.30
Fig. 1.30: (a) Cut-out (drop-out) fuse assembly (b) Isolator (link) assembly
Fig. 1.31: Typical rotating arm isolators: (a) Isolator closed and (b) Isolator open.
Surge arresters or lightning arresters (LA’s)