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TN-C-S

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  • 17-03-2017 8:58pm
    #1
    Phil.x
    Registered Users Posts: 1,734 ✭✭✭


    Is there any benefit of installing an earth rod in this system.


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    #2
    ptogher14
    Registered Users Posts: 203 ✭✭ptogher14


    A TN C S system has an earth rod


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    #3
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,595 Mod ✭✭✭✭2011


    Phil.x wrote: »
    Is there any benefit of installing an earth rod in this system.

    Yes, it is important that extraneous conductive parts are at the same potential to the ground. If not a conductive part could be at a different potential to the ground, so someone touching it could have a potential across them.

    Some may argue that in practice depending on the installation and how close it is to other installations it can make very little difference. However I think it is not wise to depend on the integrity of the wiring of other installations.


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    #4
    Phil.x
    Registered Users Posts: 1,734 ✭✭✭Phil.x


    My house is 15 years old and as far as I can see it has no earth rod. So I'm thinking about putting one in.
    There could be one but under the footpath. I've two 6sq earths and the twin and earth mains.
    The reason I'm thinking this, is I've tried to trip the sitting room sockets by touching earth and neutral together but it doesn't trip the elcb, but it trips when I use this https://ie.rs-online.com/mobile/p/rcd-testers/7943121/ so if I can get the right meter I'll check the loop impedance.


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    #5
    ptogher14
    Registered Users Posts: 203 ✭✭ptogher14


    That doesn't necessarily mean you don't have an earth rod. There's a lot of things at play in that scenario. For example if the RCD was supplying a number of circuits but there was no load on any of the circuits, a neutral to earth fault won't trip the RCD.

    Do you have an RCD or ELCB?


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    #6
    Tuco88
    Registered Users Posts: 1,051 ✭✭✭Tuco88


    Get a plugtop short out N-E inside, plug in a load to the socket circuit and the plug in the shorted plugtop. You will need ~30ma to operate it, you could use a made up one with a 60 watt bulb or something also.

    If it's a elcb it operates slightly different, if I remember its a from a voltage reff on the earth.


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    #7
    crasy dash
    Registered Users Posts: 1,605 ✭✭✭crasy dash


    Op on mobile now but go on YouTube have a Look for videos on earthing systems by John Ward find him very good explains everything from scratch.


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    #8
    Phil.x
    Registered Users Posts: 1,734 ✭✭✭Phil.x


    ptogher14 wrote: »
    That doesn't necessarily mean you don't have an earth rod. There's a lot of things at play in that scenario. For example if the RCD was supplying a number of circuits but there was no load on any of the circuits, a neutral to earth fault won't trip the RCD.

    Do you have an RCD or ELCB?

    RCD


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    #9
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    RCD and ELCB are the same thing, except if they have elcb on them, they are going to be older. There was a time when elcb`s were voltage operated though. But the current operated ones and RCDs are the same.

    The change from elcb to rcd was more of a name change as just about all elcb`s at the time were current operated. Residual current is a better description, as they can trip on some problems without actually being an earth involved.


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    #10
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    ptogher14 wrote: »
    For example if the RCD was supplying a number of circuits but there was no load on any of the circuits, a neutral to earth fault won't trip the RCD.

    It usually wont alright, but it still is possible. More unlikely on a neutralised house.


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    #11
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Phil.x wrote: »
    Is there any benefit of installing an earth rod in this system.

    If the earth rod was not installed, on the TN-C-S system, it would not be noticed operationally.

    But it is still an additional earth rod to earth the neutral conductor from the transformer, along with all the other earth rods on all premises connected to the same transformer. They are all linked via neutralizing connections.

    If the neutral into the house fails before the neutralizing link, the earth rod is now standalone on its own. Neutral voltage in the residence will rise if anything in the house is on, taking with it all bonded metal, which is why it is all bonded, to keep it all at the same potential at least, which reduces shock risk.

    The single earth rod usually does little to keep touch voltage at earth potential, unless only a tiny load is on in the house. The actual symptom is often incandescent lights barely lighting. If the earth rod wasnt there, it would be like a complete power cut with main neutral gone. The earth rod will slightly reduce touch voltage, but usually very little.

    As a side note, if the earth rod made a perfect 0 ohm connection to the ground, the failed neutral scenario wouldnt even show itself, and all would work as normal.


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    #12
    ptogher14
    Registered Users Posts: 203 ✭✭ptogher14


    Bruthal wrote: »
    It usually wont alright, but it still is possible. More unlikely on a neutralised house.

    Curiosity has me now. How can it trip with no load? Genuine question


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    #13
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    ptogher14 wrote: »
    Curiosity has me now. How can it trip with no load? Genuine question

    I changed a fuseboard to MCB. Board a fair few years ago. As often happened, RCD tripping when finished. With all mcbs off, still tripped. Then main switch off it still tripped.

    A socket upstairs had neutral and earth into same terminal. Fixed that and problem gone.

    Row of houses supplied by overhead lines. I'd say with good load on the neutral, it wouldn't be hard to see 30ma come into the house in its neutral, through rcd and to earth rod via that socket fault. If the house had been neutralised it is likely the RCD would not have tripped in the no load scenario like you say yourself. I'd say this case would be unusual.

    Undersized overhead lines were a big factor I'd say.


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    #14
    ptogher14
    Registered Users Posts: 203 ✭✭ptogher14


    That's a strange one. I'd say some head scratching went on there. Everyday is a school day and all that


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    #15
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    ptogher14 wrote: »
    That's a strange one. I'd say some head scratching went on there. Everyday is a school day and all that

    It was unusual, but was easy enough to narrow down and find. All Socket circuit neutrals removed from N bar, all MCBs off, test. Find one with the problem with tester. Same method is good for nuisance tripping of RCDs and checking for a N-E fault.


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