# Interest group forums > Electrical Contracting Industry Forum >  kA ratings

## skatingsparks

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)

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## Dave A

Or put a suitably rated resistor in the feed line to artificially boost line resistance?

(Not a qualified comment - just a thought).

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## AndyD

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. :Big Grin:

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## Sparks

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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## murdock

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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## ConcernedHomeowner

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) . 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).

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## AndyD

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?

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ConcernedHomeowner (25-May-18)

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## ConcernedHomeowner

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.

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## SeanM

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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ConcernedHomeowner (25-May-18)

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## SeanM

Sorry auto correct PSC not PC

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## AndyD

> .........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.






> 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. 




> 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. 




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

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## AndyD

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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ConcernedHomeowner (25-May-18)

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## ConcernedHomeowner

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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## ConcernedHomeowner

> 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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## ConcernedHomeowner

> 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.

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## SeanM

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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AndyD (02-Jun-18)

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## AndyD

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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## ConcernedHomeowner

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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AndyD (02-Jun-18)

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## AndyD

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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## ians

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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## ians

> 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.


we have more problem with brand new "expensive" cbi earth leakage units than we do with the good old stuff.

another good example is the good old lumex plug and light switches...the stuff last forever...replace it with an produc and it is all plastic junk.

same applies to geysers...once you replace it...you are lucky to get 5 years...some old geysers are still working 25 + years later...the old geysers had a copper drum.

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## 12mathaba

Hello everyone, I would like to know, I am using new psc tester TOP TRONICof which I am not familiar with, know when I measured the psc it gives me a value 758 amps, the main circuit breaker is 63 amps 3ka rating. My quation is this valve acceptable?

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## SeanM

Morning Mathaba

Provided your tests were carried out correctly i.e: with the load off and at the main breaker then your value is acceptable. 

758 amps reading breaker can handle 3000 amps fault current even at three phase (758 x 1. 73)

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