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Thread: kA ratings

  1. #1
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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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  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.

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    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.
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    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.

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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.

  7. #6
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    Hi

    My electricity has tripped intermitently and I haven't been able to isolate the problem. I've had three electricians visit the premises and two have advised me of work which I do not think is reasonable (for instance starting by replacing a DB board which doesn't have any faults). So I've decided to do a lot of reading because I can see that there is some good work that should be done, but I want to make sure the house is safe and meets legal requirements, without spending unnecessary money. So the first thing that people have advised me is that with age, Earth leakage breakers can become more sensitive. I have a very old Earth Leakage Circuit Breaker (see picture) Click image for larger version. 

Name:	DSC_0080.jpg 
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ID:	7115. When I came across this thread, looking up what the kA rating signified, I realised that all my individual circuit breakers are at 2.5 or 3.0 kA, including the main switch, but the Earth is at 5kA. Can anyone advise what the safe kA rating should be in Pinelands, Cape Town for a domestic installation?

    I'm going to be working with an electrician to do the actual work, but in light of past experiences, I am making sure I am informed about all matters. I will also be buying the parts myself (in light of being being quoted R600 for regular circuit breakers by one electrician, the same one that wants me to replace the DB board).

  8. #7
    Diamond Member AndyD's Avatar
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    Your intermittant tripping problem would not be caused by the circuit breaker or earth leakage breaker being of an inadequate kA rating.

    Regardless of your geographical location the required kA rating of the breakers in the DB would be determined by the PFC (Prospective Fault Current) which would either be stated by the electricity supplier or can be determined by testing. Having breakers of mixed kA ratings isn't a problem as long as they're all above the required rating.

    There's no rule of thumb that I know of that earth leakage breakers get more sensitive with age and TBH this kinda statement coming from a professional sparky as justification for a blanket replacement policy is highly unprofessional and possibly fraudulent. The device should be properly inspected for damage and ramp tested and any decision about it being fit for purpose based on those test results.

    If you find a reputable electrician then you'll probably be paying list prices (same as you'd pay at a retailer) for the materials or thereabouts because they'll get a hefty trade account discount from the wholesaler so buying your own materials generally won't be worth it; you won't save any significant amount and you'll have to carry the warranty, including the labour for replacement, at your cost if anything goes faulty in future.

    Which circuit breaker trips intermittently? How often does it trip? Does it reset immediately when it trips?
    Last edited by AndyD; 23-May-18 at 11:57 AM. Reason: fixed spelling
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  9. #8
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    Thanks for your response AndyD. It's the Earth Leakage Unit that trips intermittently. I can sometimes go three to four weeks without a trip, but then out of the blue, it will go down. Mostly it resets immediately, but there have been times when I have had to drop a circuit breaker (for almost any circuit) before I can get the Earth Leakage switch back up. At other times, it can trip every three or four days. It does happen more frequently when it rains (but not exclusively), and I note what you say about drip loops for external lights, for instance, although those lights were installed five years ago, and this intermittent tripping started about two years ago. It has happened more frequently in the last six months and I did buy and install a bar fridge in December last year.

    In researching more about my Earth Leakage Breaker, it appears that it has overcurrent protection at 30A. With the addition of the bar fridge onto my one plug circuit (which is on the same phase as my geyser), is it possible that if the fridge motor kicks in at the same time as the geyser and a few other appliances are on, it shoots the current past 30A and that causes the breaker to trip, rather than an Earth Leakage? The other factor about rainy days is that that is when my geyser will typically go on, as it is a solar geyser, and the element only kicks in when the sun doesn't get the water to a particular temperature. So the moisture from the rain may be a red herring.

    The one electrician that I worked with that didn't immediately start advocating that I spend lots of money is coming back on Saturday and he will do more tests. He has come with a good reference from someone I can trust who knows more about electrical installations than I do. So far he has given me more confidence than the others I have worked with. I will chat with him about who purchases what, but he will be the one doing the installing. I have opened my DB board to check which circuits are on which phases, but I'm not going to be installing breakers. I am reading a lot and finding out more, not so that I can rewire my house and DB board, but so that I can know what the legal requirements are and what proposals are required and which are fanciful. Based on my research I can see that a lot of the work that has been done at our house is not to appropriate standards. But I hold myself responsible for not knowing more and checking up better. We rushed forward in the past with repairs and upgrades, rather than checking facts and ensuring standards. So now I want to systematically look at matters and improve the wiring in the entire house over the next year (we will be renting it out for seven months next year, and need all things to be in good order before March 2019).

    What is your company name, or how can I contact you? If things don't work out with the electrician coming on Saturday, perhpas I can engage your services? From your profile it appears you are in Cape Town.

    On the kA rating, can I just phone the municipality then? From what someone said to me at an electrical wholesaler, 3kA is more than enough, but I'd like to be on the safe side.

  10. #9
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    Morning

    I note that you reside in Pinelands, I reside in Table View and would gladly test your PC for you at no cost.

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    Sorry auto correct PSC not PC

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