Our neutral to earth voltage is fluctuating from 2.5v to 4.5v.
We have a separate neutral earthing for UPS and DG and separate body earthing.
We also regularly applying salt for earth pits but are unable to resolve our voltage issue. Can you please guide what we can do?
Generally speaking, reducing the resistance of the earthing electrodes (salting them) will not help you with a neutral to ground line voltage issue. First of all, you must have a common earthing electrode system as required under SP30: Section 14, which requires earth-continuity conductors between all electrode systems.
Now, how do you deal with the voltage? It is almost certainly caused by an erroneous neutral-to-earth bond somewhere in your system. Have you measured the amperage on your protective earthing (PE) system? You need to trace the current on your PE back to its source. No doubt, you will find a subpanel or backup generator somewhere that has a connection from neutral to earth that should not be there and is allowing normal operating neutral currents to travel back on the protective earthing system.
You may also want to investigate your transformers and see if there is a problem forming due to an unbalance issue or failing insulation.
You may also find this refference answer useful that we posted a while back:
How can we reduce the voltage between the Neutral and Ground without using an Isolation Transformer?
The Engineering Experts at E&S Grounding Solutions