the location of the earthing point is based on the earthing system your applying to your network (TN-C,TN-S, ,TT & IT)
TN-C
In this system the neutral and protective conductor are combined , the conductor is connected between the transformer star point and the equipment neutral /earth point . additional earthing point (rods) is not required on the equipment side
TN-S
in this system the earthing and nutral conductors between transformer and equipment are not combined ( separated ), they have to be connected back to the transformer star point, additional earthing point (rods) is not required on the equipment side
TT
in this system the only nutral conductors between transformer and equipment is connecetd , the exposed conductive part of the equipment shall be connected to local earth point by means of protective conductor.
IT
its the same as TT system except the the source neutral point is connected directly to earth ,its connected through low impedance earth electrode (earthing impedance)
there is also other compination such as TN-C-S
the protective cable size selection is based on BS ≤7671
- for phase conductor size S≤ 16mm2 the protective conductor size shall be equal to the phase conductor size
- for phase conductor size between 16<S≤35mm2 the protective conductor size shall be 16mm2
- for phase conductor size S>35mm2 the protective conductor shall be 1/2 phase conductor size
Regards
Amin