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Distance between other electrical systems

Former Community Member
Former Community Member
Hi all,


I've been asked this time and time again and it could be a case that I've looked at this so much that it's made me go insane, but I'd like a 2nd opinion.


When installing a TT feeder pillar on the street, does the 2.5m rule come into effect when it's located near to a PME system or does this need to be 2.5m away from all other systems which are not connected to the same earthing system (not connected to the earth mat/rod under the feeder pillar?  


My personal opinion is that they should be 2.5m away from anything that isn't on the same electrical installation (even if it's another TT system nearby) as if there's a fault with one and the path to earth is broken then the path would flow directly between the person or whatever touches it and take the route of least resistance. I have my copies of the 18th edition and the CoP for EVCEI, but I've been looking at it for so long it's made things become less clear the more questions I'm being asked about the regs!


Any help would be much appreciated,


Regards,


S
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    davezawadi:

    Reading this makes me realise just how badly thought out EV charging is (again). Typically every multiple EV charging point is defective because each has its own electrode following the regs. Two adjacent cars can be at differing potentials. Chris is quite correct here (and BS7671 a mess) because a TT installation inherently depends on the RCD to provide shock protection, and therefore ANY fault with danger must simply trip the RCD if contacted. Simple enough and has worked very well for many years. However people are now worrying about potentials rather than disconnection on contact, which is simply not sensible.




    People are worrying about potentials which do exist ... although it's not "within the same electrical installation" or even the same means of earthing.


    Exposed-conductive-parts of a TT system are at the potential of the TT system main earth terminal (which is hopefully the potential of the earth electrode).


    The separation we were talking about is to prevent the "import" of earth potential rise from a PME installation, and has nothing to do with automatic disconnection within the TT installation. It's no good having requirements to prevent PME touch voltages, and returning them by inadequate (or, alternatively as I've pointed out, inappropriate) separation of the TT system from the PME system.



    TT does not work unless there is a potential and earth path sufficient to trip the RCD! My reading of multiple earth systems is a TN-S and a TT one, not two TT systems, because they are inherently protected from danger by the RCDs. TT islands do not work for car charging unless you trust the RCD.





    As above, probably nothing to do with the RCD - the issue is outwith the installation, although I do agree, even separation may not be the answer to this.



    Clearly some do not, and the "what if" question immediately makes all this unworkable, particularly when the H&S police have had a go too! The answer is simple and can be fixed immediately by a simple bit of legislation; "Electric vehicles must be class 2, otherwise they may not be sold in the UK". All those not complying may be sent abroad when sold, and the owners suffer a loss like my diesel car, government about turns included! Fair enough and the proper way to sort the problem, which should never have happened in the first place if those responsible had been paying suitable attention!





    Agreed, to a point - there may be other options than Class II, but Class II would have solved the problem ... unless of course there's an issue with static electricity and hybrids??

Reply
  • 0

    davezawadi:

    Reading this makes me realise just how badly thought out EV charging is (again). Typically every multiple EV charging point is defective because each has its own electrode following the regs. Two adjacent cars can be at differing potentials. Chris is quite correct here (and BS7671 a mess) because a TT installation inherently depends on the RCD to provide shock protection, and therefore ANY fault with danger must simply trip the RCD if contacted. Simple enough and has worked very well for many years. However people are now worrying about potentials rather than disconnection on contact, which is simply not sensible.




    People are worrying about potentials which do exist ... although it's not "within the same electrical installation" or even the same means of earthing.


    Exposed-conductive-parts of a TT system are at the potential of the TT system main earth terminal (which is hopefully the potential of the earth electrode).


    The separation we were talking about is to prevent the "import" of earth potential rise from a PME installation, and has nothing to do with automatic disconnection within the TT installation. It's no good having requirements to prevent PME touch voltages, and returning them by inadequate (or, alternatively as I've pointed out, inappropriate) separation of the TT system from the PME system.



    TT does not work unless there is a potential and earth path sufficient to trip the RCD! My reading of multiple earth systems is a TN-S and a TT one, not two TT systems, because they are inherently protected from danger by the RCDs. TT islands do not work for car charging unless you trust the RCD.





    As above, probably nothing to do with the RCD - the issue is outwith the installation, although I do agree, even separation may not be the answer to this.



    Clearly some do not, and the "what if" question immediately makes all this unworkable, particularly when the H&S police have had a go too! The answer is simple and can be fixed immediately by a simple bit of legislation; "Electric vehicles must be class 2, otherwise they may not be sold in the UK". All those not complying may be sent abroad when sold, and the owners suffer a loss like my diesel car, government about turns included! Fair enough and the proper way to sort the problem, which should never have happened in the first place if those responsible had been paying suitable attention!





    Agreed, to a point - there may be other options than Class II, but Class II would have solved the problem ... unless of course there's an issue with static electricity and hybrids??

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