I think there is some confusion here.
Let me first explain the technical term “TN”. It stands for Terra-Neutral. It means the neutral is always connected to terra (earth). All South African residential installations are TN installations.
That means three things needs to check out.
- If you measure the resistance between NEUTRAL and EARTH, it should be very close to zero. If you measure the voltage across neutral and earth, it should be just about zero. This has to do with the bonding of neutral and earth.
- If you measure between the earth bar inside the db board (that would be the one where the yellow and green wires, or the naked wires, are landed), and a big old peg hammered into the ground, you want to get a very low reading. I don’t remember the official value, but it is something like 30Ω if I recall. This is called the earth impedance test.
- If there is a short circuit between live and earth (as measured in the DB), enough current should flow to trip a breaker. The rule says twice the max breaker size.
Because you immediately mentioned the installation of additional earth spikes, I immediately assumed your problem is of the second type. And that particular problem can only be solved by increasing the surface area of conductive material to the earth around it, which generally means hammering in more spikes. But I would think that around 5Ω is plenty good for this.
If the issue is the first one, the bonding… then it needs to be repaired. And this is fairly simple. In a TN-C-S system, this is done at the kiosk (where your house connects to the distribution network). For a TN-S system, our supplier has to fix this.
If the issue is the third issue, the “earth loop impedance test”, then there is this bit in SANS that kicks in:
22.214.171.124 At the main switch, the impedance shall be such that an earth fault
current double the rated current (or higher) of the main protective device
automatically disconnects the supply to the installation.
So that means, if you have a 60A breaker, then a 120A or more should flow if there is a direct short to earth. With a 5Ω loop, 230V/5 = 46A, which is way less than 120. You need about 2Ω or less. But this problem will not be fixed by adding more earth spikes. This problem is fixed, likely, by replacing the main earthing conductor. Which again, in a TN-S system, involves the council.
Either there is a misunderstanding here, or someone is confusing the need for a good earth (which you can fix with more spikes) with the ground loop impedance test (which probably needs a new green-and-yellow wire somewhere).