UPS Problem

Yes.

is 62V ok?

Probably not.

Neutral to Earth Voltage Reduction Methods in Three-Phase ...

In stand alone systems, it does not matter at all. Only when two systems have a data communication between them, and, if the data zero reference is taken from the ground, the neutral-to-ground voltage does matter, as in such a case data corruption might occur, if there is an appreciable neutral-to-earth voltage. In such a system, the ideal neutral-to-earth voltage should be ZERO volts. But, practically up to about 2 volts is permissible.

Given that circuit, the output is floating. So the voltage to earth could be anything and it is therefore OK. However, the jury is out as to whether a downstream phase-to-earth fault would take out the circuit protection device in the event of a fault before someone gets hurt/killed.

Did this thing get tested and certified by a qualified Electrician before being energised?

...but do check the manufacturer's installation and use instruction leaflet just to make sure.

Just a WAG - it was a 2013 digital voltmeter and not a 1960s moving-coil multimeter, correct?

Yes dear this is a 2013 digital multimeter.

Well, then, it's probably of super-high input impedance, and because of that it's picking up a load of capacitance coupling between the supply rails and earth/ground.

• If one uses a 1960s-style AVO (usual disclaimer) to measure the voltage instead, what happens?
• If one de-energises and measures ohms from neutral to earth/ground, what happens?
• If one wires a 15W light bulb between neutral and earth/ground before re-energising, what happens to the voltage?

1.Yes voltage is the same with analog voltmeter.

2.after disconnecting the incoming supply resistance is varies from 25 to 42 Ohms.

3.When we connect a 11W bulb with Neutral & Ground the voltage remain same.

Make sure all of your earth ground connections are connected together with no or minimum resistive connections.

You may have to install a low impedance equipment system ground grid with bare copper interconnecting conductors if the soil is dry and poorly conductive.

The "earth pit" resistance can be decreased by applying a "wetting" agent such as water and/or one of the many chemicals available such as GEM directly around the ground well as per the manufacturer's directions. This works best if the entire length of the ground rod/buss down into the earth ground well is accessible.

Also:

Unless I am mistaken your drawing indicates an ungrounded/unearthed "Delta" primary (input side) with a surge arrestor network and drain to earth ground.

The point at which you attach the meter to take the readings can affect the result as you may be reading voltage drop across an arrestor and/or you may be capacitively coupled through the transformer windings.

FLUKE makes a very good ground grid testing meter that will reveal not only the impedance but the distance from the reading point to the fault (high impedance) location.