Earthing Problem

You're chasing rainbows.

The voltage between neutral and earth depends on what else is going on in the local distribution network and also the earth loop impedance. If your setup has been wired correctly according to local code then you've done all you can about the latter. If you want to do something about the former then switch everything else in the area off.

I'd be more surprised if there wasn't a voltage on the neutral.

This topic has been discussed in these pages before, so I've half a mind to report a duplicate thread.

There has to be something better to occupy your time, hasn't there, Mildred?

The line-to-line voltages are unchanged. If the impedances between phase to neutral are equal and the currents are symmetrical no voltage drop will be between source neutral and load neutral.

If these above impedances are different and the currents will be unbalanced the line-to-neutral voltages are changed and a new Nun is formed. The sum of phase_to_neutral currents will not be zero and this current will flow to the neutral source.

The unbalanced current will change a bit the source voltages to neutral too, but if we shall neglect it the source center will stay in the old Nbal center.

The voltage drop between neutrals VNun_Nbal=VanNun-VanNbal depends on the unbalance degree.

If the sum of currents Ian+Ibn+Icn=0 no neutral current will flow between neutrals and the voltage drop will be zero.

If you cannot control the single-phase currents you have to reduce the impedance between neutrals -to oversize the neutral wire for instance.

Neutral to earth is concern, not sure why though. Harmonics from conversion equipment/ferro-resonant transformer, maybe.

If you do not care about the money, moving to shielded power cables is likely to improve the noise voltages.

However, I doubt it is worth it.

(S)he is not talking about noise. (S)he is talking about neutral voltages. Shouldn't you be en route to Specsavers?

I don't think the voltage between UPS neutral and ground could be variable if this neutral is grounded [well grounded!]-it does not make any sense What I thought it is about a subpanel neutral and ground-since only UPS neutral is grounded and what it is measured it is actually the potential difference between these two neutrals.

Tripplen harmonics voltage generated in the switching circuits inside the UPS may be responsible as current due to the above voltage is passing through the grounded neutral.