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Thread: Can an Earth leakage be used as a main switch ?

  1. #11
    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by GCE View Post
    An isolator cannot trip , and therefore has no overcurrent rating , so how can it have a KA rating
    Is the limitation to disconnect under a certain fault load not an issue?

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    KA ratings ... now we taking a whole different can of worms.

    I was involved in a dispute with regards to cable size which was impacted by the ka rating (fault level) ... 2 x 70 mm cables could not be used because the fault level was too high for the cables ... which is determined by the transformer size ... cable length ... bussbars in a DB etc etc etc ... many many factors to be considered ... it would require a new thread.

    What I do see a lot are sparkies who dont have a clue and fit 2.5 ka breakers in factory environments where the DB is 5 or 10 ka rated and even has a label.

    This is a topic not many electricians understand ... which shows during investigations ... not such a big deal with domestic work ... however when working in commercial and industrial sites ... it can have a huge impact on design of the supply cabling ... the DB ... the switchgear ... the bussbars and many other parts ... in most cases ... equipment is designed and installed to reduce the fault level at the DB ... the higher the fault level the bigger tha bang ... boy have I learnt the hard way when a 1500 amp breaker tripped due to a dead short ...burnt my face ... arms and clothing ... and no I wasnt wearing the correct protective clothing ... it could have been a lot worse.

    When you start digging around in 3000 amp bussbars to try fit 3000 amp flexible current clamps with the power still on ... in crazy ... thats why I stopped doing it.

    In short ... in our part of town ... 2.5 ka is the norm for a domestic installation ... worse case senerio it might be 5 ka at the meter ... but very unlikely ... in places were eskom supply the power directly to the property (like a farm) you would find the transformer is above the meter ... in this case you would need to consider the ka rating.
    Last edited by ians; 21-Sep-21 at 07:23 PM.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Something else not many people know ... what we refer to as a geyser combo breaker ... which has a green and a white lever ... can be used as an isolator ... in fact in many cases a double pole circuit breaker can also be used as an isolator/overcurrent protection device ... the only reason they make a geyser combo breaker is due to the cost.

    In fact a good practice would be to use a 60 amp combo breaker /isolator where the cable from the meter which has an 80 amp council breaker is fed via 16 mm cable ... it would save you fitting a 60 amp circuit breaker with a 60 amp double pole isolator.

    In my opinion ... it is not good practice to use an earth leakage as a main switch ... but it is not illegal ... if you want to screw your customer for constant call fees ... fit an earth leakage as a main switch ... eventually they will catch on and dump you as their sparkie.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Good morning guys,

    Thanks for the input and feedback on this.

    Based on the comments made I do understand that there are a number of factors needing to be taken into account, a number of which I don't have the answers to at this point.

    I will discuss this with the electrician who issued the COC and try to have this resolved.

    Thanks for your assistance.

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    For the record I think 10 ka is the limit for "home made DB's" ... anything panel built with a fault level over 10 KA is subject to special approval.

    I am sure someone will correct me if this has changed.

    When you start working in panels over 10 KA ... it is good practise to wear the correct protective clothing.

    I spent many hours in induction session to prepare to work on sites like Mondi ... Alusaf ... RBM ... sugar mills etc and watched footage of explosions caused by electrical faults.

    I have also witness many accidents while working on these big sites were people has been seriously injured ... lost fingers ....lost the use their hands ... and even watched a person fall to his death from the top of the Chatsworth shopping centre.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Quote Originally Posted by Dave A View Post
    Is the limitation to disconnect under a certain fault load not an issue?
    Yes it is - Hence the reason for the isolator to be paired with a c/breaker that it has been tested with.
    If you look in the catalog you will notice that they state - " required to be backed up by a suitable short circuit protection device"

    You then need to look in the full specification for which device is suitable to be 100% correct.

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    Quote Originally Posted by GCE View Post
    Yes it is - Hence the reason for the isolator to be paired with a c/breaker that it has been tested with.
    If you look in the catalog you will notice that they state - " required to be backed up by a suitable short circuit protection device"

    You then need to look in the full specification for which device is suitable to be 100% correct.
    Are we talking about domestic installations where for example our council provides 60 or 80 amps at 2.5 ka or application where the KA rating could be higher in the panel ... for example a 400 amp DB with a 15 or 25 KA rating and you are installing sub section of the panel ?
    Comments are based on opinion...not always facts....that's why people use an alias.

  9. #18
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    Quote Originally Posted by ians View Post
    Are we talking about domestic installations where for example our council provides 60 or 80 amps at 2.5 ka or application where the KA rating could be higher in the panel ... for example a 400 amp DB with a 15 or 25 KA rating and you are installing sub section of the panel ?
    Talking all electrical installations - You work on the same principles but obviously mistakes get more expensive and dangerous the high the fault level.

    On Domestic installtions the guys are getting away with not worrying about the correct protection , which makes the coc invalid, because the fault levels are so low.
    There will be the day when he is close to the minisub , mains connection close to the boundary and the fault level is going to be higher than normal.

    My other theory is that if Electrical contractors are not made aware of the basics when they are starting out , how do we expect them to understand what happens in a factory or shopping center , when as you previously mentioned they quote to change a 10 Amp CB in a 10KA DB and think that a 3KA CB will work.

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    I had a dispute with a sparkie a while back over a circuit breaker ... he didnt even know the difference between a curve 1 /2 or 3 ... a machine was sent all the way back to Germany because the breaker was tripping when the magnet switched on ... thats why I was called out for a second opinion ... all it needed was a curve 2 breaker. When I looked in the DB ... all the breakers were the small 3 phase 2.5 and 3 ka standard white heineman breakers ... that cost the machine supplying a few pennies in freight ... Below the DB name was a label 5 KA.
    Comments are based on opinion...not always facts....that's why people use an alias.

  11. #20
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    We havent even touched on arc fault ... an AFDD unit ... lets not confuse everyone
    Comments are based on opinion...not always facts....that's why people use an alias.

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