OH Line Transformer Earthing

I really don't think it would matter if the grounding system had been chosen properly. Afterall the maximum voltage permitted at the system ground is of the order of few volts under the designed fault condition.

There is a good step by step procedure here, it too doesn't show a separate earth connection.

http://en.wikipedia.org/wiki/Earthing_systems

A is TT

B is TN-CS

No problem.

Hi Tony,

For what its worth, this is how my own service was set up in 1997.

The utility pole out by the road has a 4160/240/120V - 15KVA transformer mounted on it. NOTE: Where I live, every house (service drop) has a pole mounted transformer.

There is a bare copper conductor running down the pole from the ground lug on the transformer and the lightning arrestor to a driven ground rod at the base of the pole.

There is a second pole on my property that conveys the secondary conductors to my meter. At the meter there is a bare ground conductor from the meter cabinet to a driven ground rod at the base of this 2nd pole.

From the second pole the secondary conductors go underground via rigid steel conduit to my home service panel.

My 200A service panel has a ground conductor from the panel to the steel water pipe coming in from the well.

I agree with you regarding the need for separate (multi path)bonding. My concern is the lack of redundant bond points.

Just my 2 cents.

Great illustration by the way

Regards - KJK

In North America, at least, it has become the defacto utility standard to use a common neutral, pole ground system for both the primary and secondary distribution systems.

Why...

1) Cuts down on an additional neutral conductor.

2) Improves the realiability of their coordination systems.

One of the more esoteric benefits is that... redundent return paths, through the "single neutral" system allows for additional paths back to a source.

How does this help... if house A were to loose its neutral connection because of a failure in the consumer service drop, the chance that a ground return back to the source through a lower impedance path found in a neighbours ground electrode and then back to the common utility neutral then to the transformer, much improves the ability of the utility system to maintain the voltage levels delivered to the effected house at close to design levels.

This wont flow any, or very little, imballance current back to the source. The benefit comes from helping to ensure voltage levels stay normal or as close to normal as possible in event of a dropped neutral. Otherweise... 120v devices get connected in series across a 240v source.

Under fault conditions your fuses and mcb should isolate due to over currents.

So your earthing must be common from source to consumer point

My thinking SIR.

JS