The number of rods is dictated by the need to reduce the resistance to the correct level.
A typical substation (1ohm combined resistance) will have rods laid in a line and following the route of the cables (the trench is there so we use it!) and connected by 70mm2 bare copper.
A further 4 (single) rods will be used (one at each corner of the site) to reduce voltage gradients at the operating positions of the switchgear (they do not form part of the earth)
If we are using a split system the HV & LV earths must be separated by 10m. so will go in opposite directions with one of them being insulated for the 10m.
In older situations with an overhead network the LV earth would be connected at the first pole.
Some other overhead equipment will now have a V with the apex at the pole. Overhead switches have a mat below the operator's position.
A typical substation (1ohm combined resistance) will have rods laid in a line and following the route of the cables (the trench is there so we use it!) and connected by 70mm2 bare copper.
A further 4 (single) rods will be used (one at each corner of the site) to reduce voltage gradients at the operating positions of the switchgear (they do not form part of the earth)
If we are using a split system the HV & LV earths must be separated by 10m. so will go in opposite directions with one of them being insulated for the 10m.
In older situations with an overhead network the LV earth would be connected at the first pole.
Some other overhead equipment will now have a V with the apex at the pole. Overhead switches have a mat below the operator's position.
