Earth loop impedance Help

General Discussions
1

Hi All,

I dont know much about this, hence I am sincerely reaching out to the community. I am in the process of having solar installed and the electrician whom is wiring the 3phase DB down to 1 phase has picked up that the “earthing is too high”. It was mentioned that this should have been picked up in the CoC when I purchased the house just last year. The new electrician has advised that additional earth spikes need to be installed and wired to the DB… not sure what this means. The CoC I received when purchasing the house states a earth loop and neural loop impedance of 0.19 and no changes where made to the DB since purchase until now for the rewiring down to 1 phase.

My queries are the following:

  1. Could the rewiring down to 1 phase caused this “higher earthing” and hence the additional work needed?

  2. If earthing is needed, are the additional earth spikes the only way to fix this?

  3. Should this have been picked up by the electrician whom issued the CoC - Do I have any recourse in having this fixed by the CoC electrician?

Any other advice is appreciated as I am unsure how to proceed with this. Attached are the test pics of each phase from the electrician whom rewired the board.

Kind regards.

2

Apologies, earth test pics attached

Red phase
Red phase960×1280 183 KB

Blue phase
Blue phase960×1280 186 KB

Yellow phase
Yellow phase960×1280 186 KB

3

Welcome MaxKool

Years ago I had a similar situation. We only found it when the inverter was installed as per SSEG regulations.

The tests required for SSEG installation, brought it to our attention which means, all the years before that day, the earth connection was not on spec.

Now we have a TNC-S connection, the problem is sorted.

4

Very unlikely.

Ok, first off, disclaimer. I am not a sparky. But I would think it depends on what kind of earthing system you have. South African houses will always be either TN-C-S, or TN-S. Without getting into the details, with a TN-S system the earth spike isn’t on your property. Instead, you have an earth cable running back to the transformer. This usually provides an extremely good earth impedance. If you have a TN-S system, the correct action may be to notify the council that their earth is fooked.

If you have a TN-C-S system, then indeed, the only way is to install additional earth spikes, spread over an area, until the resistance is low enough.

Even if you have a TN-S system, installing a spike and converting it to a PME (protective multiple earth) is sometimes the only option, especially if the council cannot be bothered to fix their stuff. But if you do that, keep in mind that your shiny new earth spike could now be the lowest impedance path for the entire street :slight_smile: I think this is what happened at TTT’s place.

Yes. But that assumes that at the time it was actually wrong. Which I know sounds strange, but it is possible for an earth impedance to vary over time, and wet soil (for example) may provide an adequate reading while that same soil (when dry) doesn’t.

Because of above-mentioned reason, probably not.

Nice healthy short-circuit current estimate you’ve got there though!

5

The measurements seem to be live to earth?
For the 0.2Ohm requirement it should be N-E.

1 Like
6

True. I assumed he meant the usual test where you put three spikes outside in the ground, clamp the fourth connection to the house’s earth, and test the earth continuity.

If he was measuring the TN bond… that should be close to zero indeed.

Edit: I mean this test.

7

Here is another video of the same guy, actually doing the test in his backyard. Interesting to note, it uses the existing terminals on the Megger-branded meter. Maybe that is why it says L-E ?

8

If the N-E bond was previously 0.19Ohm, and is now ~4, something has come loose. But I suspect we are looking at 3 readings for L-E, one for each phase, or perhaps spike resistance as you mention. For spike resistance I think those readings are more than adequate (IIRC, also not a sparky).

2 Likes
9

But what are you @_a_a_a?! I’ve wondered many times :sweat_smile:

10

On the internets, I am journalist from Kazakhstan.

11

Bright Spark :slight_smile:

GlimlagGroetnis

12

For make great benefit the wonderful of energytalk!

2 Likes
13

He is number four wire puller in all of Kazakhstan!

14

Hi All!

Many thanks for the feedback thus far. Much appreciated.

Im not very clued up technically unfortunately. Should I just have the additional spikes installed? Or can I leave it be. I am totally lost on how to proceed with this.

I reached to the electrician who’s details was on the CoC. His response was that someone used his details and issued the CoC and it wasn’t done by him. He’s happy though to come through and resolve it for a price! His method was to simply bridge the live and neutral and no spikes are needed.

Please… Any guidance is appreciated. My fear is doing something that just causes more issues down the line.

Thanks again for your help.

15

I’m not a sparky, but how is bridging L and N not a dead short? And also, how is it not a felony to commit fraud on a CoC?

My neutral is connected to the earth wire from the Municipality (if I understand my system), but I don’t believe that my Live and Neutral should ever be bridged unless through a load offerring some resistance/impedance/whatever technical terms the people in the know use.

High school physics said V = I x R. And I = V / R. And I don’t want to be dividing by 0!

16

Contact the lawyers that handled your transfer and ask their opinion. It was their client’s responsibility to do this. Obviously the electrician is lying, or the lawyers have a much bigger problem on their hands. They should sort it out.

A CoC is supposed to be valid for two years. I had a similar problem with a water CoC (Cape Town) when we sold our house just over two years after buying it (don’t ask) and the new plumbers pointed out a whole bunch of issues. Original lawyers got the original plumber back to fix everything at his own cost.

Get another electrician and report your conversation to your municipality as well. Would probably mean an entirely new CoC is needed, but sounds like you want it anyways.

17

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.

  1. 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.
  2. 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.
  3. 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:

8.7.5.1 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).

1 Like
18

How common is TT Earthing System in SA?

I had to convert to TT in my house due to some old and strange cabling and logistics. Many things (TV and some other appliances) were dying before it…

Is it legal, common, rare?

19

I have no idea how common it is. With TT earthing, good earth leakage protection is absolutely essential, because you cannot rely on overcurrent protection, simply because the loop impedance is too high. But as far as I can see, if you have good residual current protection, it is a good system. Wikipedia says it is preferred for telecommunication stations, due to the lower interference.

20

So, @Maxkool , I do apologise for the heap of shop talk, but you need to find out two things.

  1. Is your system TN-C-S or TN-S? Or in layman’s terms, is the earth spike on your property or up the street at the transformer?
  2. What exactly is the problem. Is the earth loop impedance too high (which has nothing to do with the number of spikes in the ground, it has to do with the quality of the earth connection back to the bonding point, iow it is a cabling issue), or is the resistance between your earth and the actual soil outside too high (which can only be solved by adding more spikes)?

The answers to the second one will tell you if you can solve it with more spikes. The answer to the first tells you if you are even in a position to do anything about it.

I hope that helps.