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Thread: No incoming earth again (and again, and again and again )

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    No incoming earth again (and again, and again and again )

    Hi there

    How do you guys get around the problem of there being no proper incoming earth from the municipality side? I waste so much time in trying to get someone out who understands the problem.

    Over half the project we have worked on in the last 3 months have no proper incoming earth - one was 55 million rand commercial building with a fresh COC!!

    The Main Border box with the main switch backed onto the Mini sub - fault current to earth around 100 amps on a 400 amp main switch. (I know you are supposed to do it by calculation but I always test with my Fluke after finding so many problems)

    The one I'm looking at now - I can see its supposed to be TN-S, I can see a separate earth, but when I do a loop test at the mains position its just way to high (fault current around 30 amps on a 63 amp main switch).

    Checked with 2 different meters.

    I mean am I just unlucky of are there that many properties with bad earthing arrangements.

    The local guys (who seem to have just given up) say bang a earth spike in. For me TT is a bit of a kak system. Don't trust it so much.

    I figure if I can see a separate incoming earth I want a TN-S earthing system.

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by skatingsparks View Post
    I figure if I can see a separate incoming earth I want a TN-S earthing system.
    We certainly stick to our guns on that too.

    Over the years we've managed to track down who to call in a fair number of the regions within Ethekwini Municipality so that the problem actually gets attended to. But yes, it's frustrating. Maybe get a secretary who is good at nagging??

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    Morning
    Looking for an item in the code this morning and remembered the thread and got sidetracked.
    At first I thought we had ammo within the code to force the supply authority to provide an earth but after wading through it, 8.6.5.2 puts the ball squarely back into the contractors court of problems to solve at an extra expense.
    We are fortunate in our area that the Municipality does react to requests on bad earth readings, and have have on a couple of occasions found the star point not earthed or the earth stolen.


    5.2.3.1 A new electrical installation shall not be connected to the supply
    unless the supply includes a protective conductor. (See also 6.11 and 8.5.3.)

    6.11.1 Each installation shall have a consumer's earth terminal (see 3.17) at
    or near the point where the supply cables to the installation enter the building
    or structure. All conductive parts that are to be earthed (see 6.12.3) shall be
    connected to a main earthing terminal (see 3.28.4), which shall be
    connected to the consumer's earth terminal. The consumer's earth terminal
    shall be earthed by connecting it to the supply earth terminal (see 3.78) or
    the protective conductor (see 3.14.8) and, if installed, the earth electrode.
    The effectiveness of the supplier's protective conductor shall be determined
    in accordance with 8.6.5.

    Table 8.2 — Earth fault loop circuits for different distribution systems

    NOTE 2 The TT system relies on a low-impedance earth both at
    the source transformer and at every consumer's installation. This
    system is impractical in most parts of Southern Africa due to high
    soil resistivity and conductor losses. It has the added disadvantage
    that the loss of earth connection is not inherently self-monitoring.
    The system is not recommended for use in South Africa.

    8.6.5.2 If, for practical reasons, the requirement in 8.6.5.1 cannot be
    complied with, as an alternative, an earth fault detection and disconnecting
    device may be installed at the supply to the installation. The earth fault
    detection and disconnecting device should be so installed that it operates at
    a current related to the earth fault loop impedance which will limit touch
    voltages to 25 V under short-circuit fault conditions for a period not
    exceeding 5 s.

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    The point is that if it's a TN-S earthing system then surely the separate incoming Earth with the supply cable should be earthed from the municipality.

    If its over lines with no separate Earth then yes - it TT and I stall Earth spikes and Earth leakage. But this TN-S - I want that Earth to be there

    I found that the neighbours house, next to the one I'm working on, same story. Insufficient Earth fault loop impedance for a TN-S system - guessing the whole road is the same

    The thing is I'm finding this, and I don't think I'm exaggerating, most of the time.

    Home owners are not aware there supply Earth is missing - the house is wired with the appropriate protective devices for TN-S.

    If something goes wrong (fault/shock/fire) who is at fault when things don't disconnected fast enough? They will come back to the electrician who did the CoC. Maybe they tested everything correctly at the time. Surely municipality must rectify if a TN-S earthing is not connected.

    I see a lot of the time they just link Neutral and Earth at the pole..... So what earth system do I have now? I see in the border box a separate earth coming in with the supply. From what I see it TN-S at teh pole just outside the property they link N and earth and from that point its TNC-S? If the neutral goes missing.... and teh implications of such an earthing system.

    I see in the UK now (18th edition of BS 7671 coming into force soon) there are times when it is required to put an earth spike in when a TNC-S system is used because if that neutral goes missing where does voltage sit...
    Last edited by skatingsparks; 06-Nov-18 at 08:39 AM. Reason: bad grammer/spelling

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by GCE View Post
    8.6.5.2 If, for practical reasons, the requirement in 8.6.5.1 cannot be
    complied with...
    Is it a case of the supply authority cannot supply a protective conductor to standard?

    I suggest the answer is "No" when it comes to municipal supplies. If the supply authority fixes the faulty joint/replaces the stolen length of conductor/add other reason here, 8.6.5.1 can be complied with.

    If we're talking about an alternative supply such as a generator or PV system, another story. I suggest that is when 8.6.5.2 should come into play...

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