Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 19 replies
  • Subscribers 32 subscribers
  • Views 4987 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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
Parents
  • 0
    I think you reading of the letter of the regs is correct, and two adjacent but isolated TT zones need to be out of reach of each other. (or two of any systems that are not linked for that matter)


    However, regs aside, if the terra -firma earth potential is dangerous,  short of levitation , I'm not sure how you get more than 2.5m off the ground.

    However,  if you accept the surface of the road/grass verge as safe to touch, then by extension you have to ask if  you then accept fence-posts and so on that are accidental TT electrode like structures, just with no wiring to them, and if you do,  is it any more dangerous than a deliberately TT earthed object ?

    In reality TT is different, but the rules as written do not handle it well, in the same way there is no regulatory distinction of solidly earthed (water main bonded to PME earth next door) and loosely earthed objects (that fence post in the garden), yet the dangers they pose are very different.

    I fear you cannot win.


Reply
  • 0
    I think you reading of the letter of the regs is correct, and two adjacent but isolated TT zones need to be out of reach of each other. (or two of any systems that are not linked for that matter)


    However, regs aside, if the terra -firma earth potential is dangerous,  short of levitation , I'm not sure how you get more than 2.5m off the ground.

    However,  if you accept the surface of the road/grass verge as safe to touch, then by extension you have to ask if  you then accept fence-posts and so on that are accidental TT electrode like structures, just with no wiring to them, and if you do,  is it any more dangerous than a deliberately TT earthed object ?

    In reality TT is different, but the rules as written do not handle it well, in the same way there is no regulatory distinction of solidly earthed (water main bonded to PME earth next door) and loosely earthed objects (that fence post in the garden), yet the dangers they pose are very different.

    I fear you cannot win.


Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines