NER Body Termination And Cable Sizing

Would suggest following:

1. Connect grounding point of neutral earthing resistance to its dedicated earth.

2. Connect metal frame of Enclosure to Station Earth.

3. Interconnect Dedicated earth of NER and Station Earth.

Reasons being:

1. NER needs testing at planned intervals and whenever it has carried earth fault current and its High Temperature Warning has sounded. Hence the earthing connection shall be such that we can disconnect NER from earth keeping its frame work still grounded for safety during HT testing.

2. It is likely that during earth fault potential of NER earth will rise and hence if the Station Earth and NER Earth are not inter-connected any person in contact with Station Earth can be subjected to potential of NER earth which in close vicinity of other equipment. If all earthing pits are bonded together, then practically equipment body and NER earth at same potential at all times.

Regarding sizing of cable of earth follow local codes which mostly specify size of earth conductor to maximum fault current and duration it has to carry subject to size not being less than minimum cross-section from Mechanical Point - hence though size of conductor may work out to small for the current it has to carry but applicable code of your area may specify minimum desirable size of earth conductor.