Earthing switches are usually installed in combination with an isolator and the two should be interlocked electrically or mechanically to ensure that the isolator is open before the earthing switch is closed, and conversely that the earthing switch is open before the isolator is closed.
The table below summarises the normal equipment ratings for fuses/switches.
|Rated current (switches)||00 A||00 A|
|Rated current (switch fuse units)||00 A||00 A|
|second through fault capacity||0 MVA||00 MVA|
|Breaking capacity (switch fuse units)||> 0 MVA*||> 00 MVA*|
*Breaking capacity determined by fuses used
It is important that the correct HRC fuses are used. Fuses used in air are different to those of identical current rating but designed to operate under oil for heat dissipation reasons.