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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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  • 0

    mapj1:

    I am not aware of any equivalent distance rules for caravans and boats, that prevent say a cold water supply pipe in  a marina, from being bonded to the PME supply in the building where it originates, but that is also PME earthed metal.  If you had a distribution pillar and meters in a boat yard,  if it is the end of the PME service, there will be an electrode on it, even if all the loads are wired as TT.




    As per earlier post in the thread, see BS 7430, and GN 7 (Section 7.5.6 and Figure 7.3) ... these are not new for the 18th Edition updates either.



    In terms of is it a real problem, actually the current regs require all properties to bond cold water pipes if they are metal, and no insulation section, and I am aware of a few round here, where one house is PME and the one next door is TT. Many such earthing systems are already linked, like it or not  - that is why we do see quite large diverted currents on the pipework sometimes, but it all works OK.





    Does this satisfy the DNO's requirements for separation of TT systems from the Global Earthing System? If so, in those cases, perhaps OK and I'd agree what's the difference. But this may not be the case in every installation.



    As I said above, the rules are written such that in  small space you really cannot win.

    Which probably means the rules need a rethink for this case.



    Don't disagree ... especially where EV charging is considered.

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  • 0

    mapj1:

    I am not aware of any equivalent distance rules for caravans and boats, that prevent say a cold water supply pipe in  a marina, from being bonded to the PME supply in the building where it originates, but that is also PME earthed metal.  If you had a distribution pillar and meters in a boat yard,  if it is the end of the PME service, there will be an electrode on it, even if all the loads are wired as TT.




    As per earlier post in the thread, see BS 7430, and GN 7 (Section 7.5.6 and Figure 7.3) ... these are not new for the 18th Edition updates either.



    In terms of is it a real problem, actually the current regs require all properties to bond cold water pipes if they are metal, and no insulation section, and I am aware of a few round here, where one house is PME and the one next door is TT. Many such earthing systems are already linked, like it or not  - that is why we do see quite large diverted currents on the pipework sometimes, but it all works OK.





    Does this satisfy the DNO's requirements for separation of TT systems from the Global Earthing System? If so, in those cases, perhaps OK and I'd agree what's the difference. But this may not be the case in every installation.



    As I said above, the rules are written such that in  small space you really cannot win.

    Which probably means the rules need a rethink for this case.



    Don't disagree ... especially where EV charging is considered.

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