Hi Everyone. I would appreciate some thoughts on the following.
This is the Durban area which is normally TN-S earthing arrangement. I have recently installed a new DB at our remote workshop as the existing supply point was shockingly non compliant. No main earths, isolators feeding 63A sub DB's with 4mm cable two core (insulated live and bare neutral), 63A welding sockets fed directly from the 125A main switch and no earth leakage etc etc.
This area is supplied from Eskom. There is a pole mount transformer supplying ABC to a meter box. From there the supply enters our installation. It would seem that Eskom has not run earths and are using the TN-C system (no earth in their meter box). All the existing earths in our installation were bridged to neutral at the main incoming DB and the other two sub DB's.
After doing the changeover I energised up to the main switch and carried out a ELI test. As the main switch is 125A I was expecting double that as per SANS. However, the readings were 21 ohms and 10.5A on L-N-E. Clearly way off. The testing of L-N-N has generated the correct results. I then took a walk down the road to the pole mount transformer and noticed that the earth from the star point has been cut up the pole.
Now my concern is if I connect neutral to earth at our main DB (TNC-S) what would happen should there be a fault at the installation and the main neutral is faulty. Where would this fault current and voltage go to. I have installed three earth spikes at the main DB to help with the earthing but need to ensure that any metal equipment would not become live in the event of a fault on an appliance etc.
This is the first time that I have come across this and I am unsure of how to proceed so any comments would be appreciated.
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