Floating neutral

[FRENCHIE]

Hi GCE.
Spoken to GE technician today and this is what he had to say.
He has commissioned the UPS but warned us that we have a floating neutral but that it will not affect their equipment.

Now the issue is that the client is a bit confused who is right or wrong.

We are concerned that we have a floating neutral and that we must sorted it out.
We have done all our test and per the sans they are all perfect reading.
But saying that GE technician insists that we have very earth, we did loop impedance test and according to our calculations the earth is fantastic, the other thing is that he does a resistance test and reading fluctuate from 0.5 Ohms to 1.3 Ohms continuously and he maintains that that the reading what ever it is should be stable and not erratic, as we said to him our sans doesn't require us to do that test as our voltage neutral to earth is 0.125 Volt and we far below 25 Volt dangerous level and 50 Volt we disconnect the installation.

But he still maintains that we have bad earth
We have done our earth continuity test from the mini sub through the MLVP to the MRI isolator which feeds the UPS and its 0.01 Omh with a 100 Meters of 16mm PVC wire.

Now we get from the 315KVA mini sub earth bar to the ground earth test 6 Ohms, GE say that we must have 0.00 Ohms.

We have request that a GE fully pledged electrical guy comes to retest the system, as we are not really satisfied with the previous guy demands.

Do you perhaps think that maybe that we are not being compliant with our 6 Ohms at the transformer earth.

We have always been under the impression that 0 Ohms to 10 Ohms unless the Engineers requests a special earth requirement of 0 or 1 Ohms.
Thanks
FRENCHIE

[GCE]

Hi Frenchie

SANS 10142-2 , asks for an earth resistant reading of less then 1 ohm on a mini sub.So the GE tech could be right that his earth is not sufficient .Have pasted reg below

6.2 Installation of a neutral earth and bonding
6.2.1 The earth electrode shall be installed as close as possible to the transformer and shall have
an earth resistance not exceeding 1 Ω.
6.2.2 The transformer tank shall be bonded to the earth stud and to the substation earth bar.
6.2.3 The LV neutral of a transformer shall be bonded to the earth stud.
6.2.4 The earth stud shall be connected to the earth electrode.
6.2.5 All bonding and earthing conductors shall be of cross-sectional area at least 70 mm2 copper
or equivalent, unless it can be shown by calculation that a smaller cross-sectional area will suffice.
6.2.6 Earthing terminations shall be installed individually and in such a way that they can easily be
accessed and disconnected for routine earth testing.
6.2.7 The neutral earth resistance shall not exceed 1 Ω.