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Thread: kA ratings

  1. #1
    Bronze Member
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    kA ratings

    Right, just making sure of myself before i tell someone on site to naff off. I did an estimate for a shop fit with an existing DB and in the estimate at the bottom I put that "its is assumed that the existing installation and any part to be reused is compliant SANS 0142". Now I looked at the board, it looked ok, the sparks on site ran a new sub main to it, not my problem down to them to COC that. Now when I do the COC for these shops I always state that the COC only covers work that I have done and does not cover anything prior to the DB, reason being you can shut down large sections of shopping centers to inspect submains, they won't allow this and sign the COC where they should accepting this. Now I did my dead tests, earth continuity, Insulation resistance etc. All perfect. Now I do the Earth Fault loop Impedance and PSC at the board and find the prospective earth fault current is 7.7kA, Higher than I thought it would be but I trust my Fluke 1653B. The breakers protecting the existing circuits which i haven't touch altered or changed in anyway have 2.5kA breakers on them. The main switch is a 63 amp circuit breaker rated at 6kA and the earth leakage covering the Sockets is 63 amp 30mA with breaking capacity of 2.5kA.
    Now I am going to fit a breakers with breaking capacity of 10kA to cover the circuits I have installed(4 lighting circuits and 1 socket circuit).
    The problem is that the guy on site says can't be 7.6kA and won't change the main switch to a higher kA rating and I say well I won't sign the COC. Its not unfeasible for a fault to occur at the DB(cable trapped in door or cover isn't unheard of) which could have a very high fault current, certainly enough to destroy a breaker rated at 2.5kA. I am not signing of any of the existing circuits connected to the board. I figure they changed the sub main thus changing the characteristics of the board and those circuits.

    So am I right in saying that I am not responsible for the existing circuits if I state as such in the COC and put in section 3 only the circuits which i have installed and I am right to insist on them changing the main switch to be able to cope with the possible fault current that could occur to enable me to sign of the work I have done. Your opinion appreciated.

    By the way the DB (fed in 3 core 16mm SWA) is just a few meters away from the main incomer, reason for high PSC

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    mikep (07-Jan-15)

  3. #2
    Site Caretaker Dave A's Avatar
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    Or put a suitably rated resistor in the feed line to artificially boost line resistance?

    (Not a qualified comment - just a thought).
    The trouble with opportunity is it normally comes dressed up as work.

  4. #3
    Diamond Member AndyD's Avatar
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    PSC is a complex area. For the socket and lighting circuits the first 5 meters of a circuit can be considered fault free. This only applies up to 4mm cabling however. If you take this into account is there a big difference between the PSC values indicated by your tester and values made by manual calculations on the same circuit?

    You could always do what the council or Eskom do and supply a 60 amp DB with a 6mm cable. That should sort out the PSC issues.
    I am special and so is Vanash.

  5. #4
    Gold Member Sparks's Avatar
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    As you say, you are solely responsible for the correct installation of your addition/alteration. You must just make sure that you detail all your work correctly on the COC and that you also stiplulate clearly which parts of the installation are excluded. Be sure to have the recipient sign in the provided place on the COC. Then he cannot deny knowledge that the original installation is not covered. Unless of course you get commisioned to certify the entire installation.

  6. #5
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    Oct 2007
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    my advice would be make sure you have all your calculations correctly worked out for you ka rating and documented with all relevant information...starting at the transfomer...cable sizes...buzzbar sizes...dont only rely on the 1653...i have faith in my 1653...but wouldnt even consider challenging anyone just with the results from the 1653.

    the last dispute i went into with another company...i had a file 30 pages of info...downloads form the internet....all the relevent sabs regulations etc...when i opened the file...and the other person realised that i had done my homework...and didnt have aleg to stand on...within a couple of minutes...just turned to the customer and said he would send a team to sort out all the issues.

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