Results 1 to 3 of 3

Thread: Domestic Earth Fault loop at mains position - convert to TNC-S?

  1. #1
    Bronze Member
    Join Date
    Mar 2008
    Posts
    174
    Thanks
    2
    Thanked 36 Times in 30 Posts

    Domestic Earth Fault loop at mains position - convert to TNC-S?

    Hi all

    I don't usually do domestics but when I have (just to keep good customers happy), I'd say about a third of the time there is nan insufficient earth from the supplier side, despite being set up as a TN-S earthing system.

    On a domestic property in a nice area of Jo'burg we have just rewired I started to test for the COC. Test between each phase and earth, yes there is 230 volts (+/-). When I do the loop test at the mains position the Ze is 4.4ohm and fault current of 56 amps.

    Its a 3 phase TN-S earthing system. I do the same test between phase and Neutral (to get PSCC) and that comes back ok (0.38 ohms and fault current of 590 amps on a 80 amp Main MCB, its at the end of the road so I figure its quite away from the sub-station of the local feeder pillar).

    Now I know the fault current has to be at least twice that of the main breaker.

    Every time I get this, I get the customer to call the municipality to log a problem and they send a member of the city power bakkie brigade out with a battered multi meter who check between live and earth and they confirm there is voltage. I get the my loop tester out and explain that the problem is not the voltage but the lack of earth. I perform the test in front of them and then show the results and they look at me like I am speaking mandarin.

    I have seen city power convert from what is supposed to be a TN-S to a TNC-S earthing arrangement. Is this the norm for SA sparks?

    Sometimes they have added an earth spike as well. It depends on who rocks up.

    Do you guys just link out Neutral and earth at the mains position? I kind of figured - its before the main switch - not my domain.

    The UK system is clearly marked if it has PEN conductor for a TNC-S earthing system. How can you just assume its a PEN conductor?

    How do you guys deal with this. Last time I had this I went back to site 5 times to meet with city power before I got someone who had a clue what I was talking about and they dug up a bit of the road and sorted it.

    On this particular job I can see the incoming Earth, it is definitely set up as a TN-S earthing system. Yes, I could put and earth spike in and an earth leakage and have a TT system but they are a pain in the backside as far as I'm concerned because of the nuisance tripping. Not a good solution as far as I'm concerned

    How do you guys resolve this?

    Oh, by the way the neighbouring house to the left - perfect earth reading. The house to the right, same problem as me. No earth.

    Surely the municipality must make this right. The mains incoming position is on the boundary wall so it is there problem - Right?

    What do you guys usually do? Everytime this happens I just end up going back and forth? Or is that just part of the process?

  2. #2
    Site Caretaker Dave A's Avatar
    Join Date
    May 2006
    Location
    Durban, South Africa
    Posts
    20,979
    Thanks
    3,055
    Thanked 2,462 Times in 2,067 Posts
    Blog Entries
    12
    We don't get the customer to call in to log the problem - we do it ourselves so that we have a report reference number handy. It also means they know which sparky they're dealing with. It shouldn't make a difference, I know - but reality is... it looks like it does.

    Quote Originally Posted by skatingsparks View Post
    How do you guys deal with this. Last time I had this I went back to site 5 times to meet with city power before I got someone who had a clue what I was talking about and they dug up a bit of the road and sorted it.
    We used to have this nightmare too, but this has proved to be one of the areas where joining the ECA (SA) has proved quite useful. After a couple of run-arounds, I've pulled in our local ECA branch technical advisor who has called (some inside contact) at the municipality and magic happens.

    After a few rounds of that - we don't seem to get the run-around as much anymore.
    The trouble with opportunity is it normally comes dressed up as work.

  3. Thanks given for this post:

    skatingsparks (09-Jul-16)

  4. #3
    Bronze Member
    Join Date
    Mar 2008
    Posts
    174
    Thanks
    2
    Thanked 36 Times in 30 Posts
    We are member of the ECA as well. I'll go there Monday to see if they know who to talk to. I have number for some areas of Joburg where I can call the one of the city power people who knows what they are doing but it seems they cover certain areas. If I have a problem in Crown Mines, no problem I can call a guy direct but I haven't got a number for this particular area of Jo'burg - Houghton. Maybe the ECA has the magic number.....

    Like I said usually when this happens they send out, usually 4, different guys before I get someone who understands.

    The guy who came out yesterday had no idea of earth fault loops () and short circuit currents () or anything, other than 230 volts between live and neutral .

    It blows my mind that they send people out without the basic knowledge of what they are working on with just a multi meter to work on something that can kill you.

Similar Threads

  1. Earth loop impedance and prospective short circuit (PSC)
    By mikilianis in forum Electrical Contracting Industry Forum
    Replies: 11
    Last Post: 21-Jan-16, 04:10 PM
  2. [Question] Earth Loop Impedance on COC test.
    By Jasond MIE in forum Electrical Contracting Industry Forum
    Replies: 8
    Last Post: 06-Mar-15, 01:42 PM
  3. Earth loop impedance testing
    By ians in forum Electrical Contracting Industry Forum
    Replies: 6
    Last Post: 10-Apr-14, 02:12 AM
  4. [Question] Earth Loop (Can it be achieved?)
    By Neal in forum Electrical Contracting Industry Forum
    Replies: 2
    Last Post: 19-Jun-13, 12:49 AM
  5. Mains voltage logger
    By duncan drennan in forum Technology Forum
    Replies: 16
    Last Post: 05-Feb-11, 03:33 PM

Did you like this article? Share it with your favourite social network.

Did you like this article? Share it with your favourite social network.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •