ELI Way out of Spec

[RegElec]

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.

[Derlyn]

For any of your protective components to operate on an earth fault, your neutral and earth must be at the same potential, so I would suggest earthing the incoming neutral that enters your property just before your main switch.

Of course, first prize would be for Eskom to earth the transformer's star point then your earth spikes will be effective. Without the star point of the transformer being earthed, your earth spikes are ornaments and don't serve any purpose.

[GCE]

I Agree with Derlyn

Further to that and a problem that could occur by earthing the earth neutral - How big is the pole top transformer , and how many dwelling/erf does it feed .

With only you earthing your neutral , you will now become the star point for the neighborhood and if your cable are a bit light they could melt and or end up with burnt connections on the star point so be careful where you do it

[Dave A]

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.

I wonder how widespread that problem is nowadays.

[RegElec]

I Agree with Derlyn

Further to that and a problem that could occur by earthing the earth neutral - How big is the pole top transformer , and how many dwelling/erf does it feed .

With only you earthing your neutral , you will now become the star point for the neighborhood and if your cable are a bit light they could melt and or end up with burnt connections on the star point so be careful where you do it

Thanks for the replies. The comments are as expected. I have bridged the earth / neutral in the main DB and left the sub DB's as TN-S. We will just have to monitor the conductors as I doubt I will get any luck with eskom to replace the earth wire at the transformer although I will try.

[GCE]

Thanks for the replies. The comments are as expected. I have bridged the earth / neutral in the main DB and left the sub DB's as TN-S. We will just have to monitor the conductors as I doubt I will get any luck with eskom to replace the earth wire at the transformer although I will try.

I would rather have done it at the meter box if possible at least then i would not have contravened 6.1.6 and if there is a huge surge down neutral earth bond it would happen outside
I say that not knowing cable sizes , positioning etc


SANS10142-1
6.1.6 The neutral conductor shall not be connected direct to earth or to the
earth continuity conductor on the load side of the point of control except as
allowed in 7.16.4.

[RegElec]

I would rather have done it at the meter box if possible at least then i would not have contravened 6.1.6 and if there is a huge surge down neutral earth bond it would happen outside
I say that not knowing cable sizes , positioning etc


SANS10142-1
6.1.6 The neutral conductor shall not be connected direct to earth or to the
earth continuity conductor on the load side of the point of control except as
allowed in 7.16.4.

Noted. I have access to the meter box so I will see whether it can be done there.

[RegElec]

Noted. I have access to the meter box so I will see whether it can be done there.

I think I jumped the gun there. I cannot join the earth neutral at the kiosk / meter box as there is no earth there. The supply to the kiosk is via aerial bundled conductor and there are only three phases and the neutral which is connected to a dumpy insulator but no earth termination is present.

[Derlyn]

If you hit in a spike at the kiosk and connect to the neutral then the earth spikes on your installation aren't ornaments anymore and the ELI test should be successfull.

[RegElec]

If you hit in a spike at the kiosk and connect to the neutral then the earth spikes on your installation aren't ornaments anymore and the ELI test should be successfull.

Thanks Derlyn. I appreciate the input and I may have to do this as I cannot see Eskom rectifying the problem.