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Thread: kA ratings

  1. #11
    Diamond Member AndyD's Avatar
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    Quote Originally Posted by ConcernedHomeowner View Post
    .........In researching more about my Earth Leakage Breaker, it appears that it has overcurrent protection at 30A......
    I'm not sure if those old Heinemann RCD's had overload protection, I suspect not because there's an overload main breaker (MCB) to the left of it so that would be duplicating overload protection if it does. The 30A it states on the front might be an indication of the maximum load it's rated to be able to disconnect at if there's an earth leakage fault. Maybe another member here has a better memory than me and can confirm if it has overload protection.



    Quote Originally Posted by ConcernedHomeowner View Post
    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.
    Earth leakage is a cumulative problem and even more so with a 3-phase RCD. It sees the total leakage on all 3 phases and if that total leakage exceeds 30mA it trips. Generally speaking it's better to have 3 separate single phase RCD's, it's causes a lot less inconvenience if there's a tripping fault and that alone may be good enough justification to replace it assuming there's space in the board for 3 single phase units and 3 associated neutral bars. As you say earth leakage tripping faults can be confusing if you're trying to solve them by deduction, I made a thread somewhere with advice for homeowners with tripping problems, I'll see if I can find it later and post a link here when I've got more time.

    Quote Originally Posted by ConcernedHomeowner View Post
    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).
    I feel for you and you're in the same boat as many home owners, sometimes they've unknowingly been let down by unscrupulous contractors and sometimes they're to blame for knowingly cutting corners to save money. I'm afraid the electrical legislation holds the home owner as being the person responsible for the electrical installation and its compliance.

    Quote Originally Posted by ConcernedHomeowner View Post
    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.
    3kA would usually suffice, especially on a 40A main supply but it could be higher if for example you happen to be close to the Eskom transformer or if for some reason you have an oversized supply cable. You could enquire with the municipality but it might be a tedious process, the best way to be 100% sure would be to test the PFC which would take a sparky with the right test equipment literally 2 or 3 minutes.

    Thanks for the offer to engage my services but I'm afraid I'm not set up to do domestic electrical, primarily I design and build control panels for the commercial market. I'm also located near Noordhoek which is nearly an hour from Tableview. Maybe take up SeanM on his kind offer of a free test, I'm sure he'd also give you some good advice on your best way forward as well if he sees the DB first hand.
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  2. Thank given for this post:

    ConcernedHomeowner (25-May-18), Dave A (25-May-18)

  3. #12
    Diamond Member AndyD's Avatar
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    Here's the link I promised to the thread about earth leakage tripping faults. https://www.theforumsa.co.za/forums/...RCD)-Tripping?
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    Thanks for the offer SeanM. Let me see what tomorrow brings. I may contact you to setup a convenient time next week.

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    Here's the link I promised to the thread about earth leakage tripping faults. https://www.theforumsa.co.za/forums/...RCD)-Tripping?
    Yeah, I read that whole thread after my original post here (or before, I can't remember). I can see there are a lot of overlaps, and that thread definitely helped me. I do have a separate single phase Earth Leakage Unit that was used for a previously installed hot water unit which we took out when we installed the larger solar geyser. (We had a small geyser and a separate instant hot water unit.) It is still sitting in the distribution board, and based on the necesity that geysers now need to be on ELU (wherever they are in the house), I think I will simply take the geyser off the main ELU and connect it to that single phase ELU. That single phase ELU also has the advantage of being on phase one (rather than phase three where all my plugs are), so the load will be better balanced on the phases as well. I currently have swimming pool and lights on phase one, external cottage on phase two, and plugs and geyser on phase three. The swimming pool and the geyser have timers, so I can ensure they never run at the same time (unless I do a manual overide of course). The stove is a three phase stove on all the phases, but not on ELU, but with proper dedicated stove connector and nothing else on the circuit, which I understand is according to 10142 standards. The single phase ELU is also connected to an energy control unit that turns it off when the stove is on. So just that move may sort out the tripping problem currently experienced. We'll see.

    Thanks for all your input. I'll keep you posted with progress.

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    I'm not sure if those old Heinemann RCD's had overload protection, I suspect not because there's an overload main breaker (MCB) to the left of it so that would be duplicating overload protection if it does. The 30A it states on the front might be an indication of the maximum load it's rated to be able to disconnect at if there's an earth leakage fault. Maybe another member here has a better memory than me and can confirm if it has overload protection.
    I can't say for sure. Based on their current products, the 63A RCD does not have overload protection, but they have numerous RCDs with overload protection, one of which is 30A (see picture). But I searched online for information on the EL 32-B and could not find anything written about it. I could probably contact CBi.

    Click image for larger version. 

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    Good Evening

    I would like to confirm when testing three phase PSCC, you test each phase and multiply the reading by 1.73

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  10. #17
    Diamond Member AndyD's Avatar
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    Yep, for 3 phase if would be the highest phase to neutral reading multiplied by 1.732 (square root 3) unless you have a tester that's rated to test phase to phase. Generally for rule of thumb I usually just work on double the single phase reading to err on the side of caution.
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    Just checked with the product manager at CBi and the old RCD was manufactured in 1974, and it does have overload protection built in. Had it tested today and it is in good working order. It trips at 20mA which is at its spec. PSC also done, and highest reading was 0.88 (so multiplied by 1.732 gives me 1.52416). Seems all the breakers are well within spec, with the lowest at 2.5 kA. Thanks for all the input.

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  13. #19
    Diamond Member AndyD's Avatar
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    Thanks for the follow-up info, it's always nice to know the outcome and I'm glad to hear you got some reliable info from the manufacturers. It's also good to hear your RCD is still functioning within its I∆n spec even after 44 years.
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    Generally white lever CBI breakers have overload protection...but can be used as an isolator if the correct number of poles are used.

    green ones dont have overload protection...nomally used to ISOLATE a circuit only.

    just to put a spanner in the works...an orange lever cbi is a curve 1 breaker also has overload protection...but can withstand startup currents and can be used where big magnetic tables are used ( a curve 2 breaker can also be used for magnetic tables as per manufacturers specs) ...you need to understand these breakers before installing.

    then of course you get D curve breakers...etc...etc we wont confuse the matter.

    A note with regards to KA rating...if your equipment is installed close to the supply transformer 500 kva and bigger...make sure you know what you a re doing...you dont want to get caught out using under sized cables...no mater how much you reduce the KA using buss bars...cable length etc to reduce the fault level.

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