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 9 replies
  • Subscribers 38 subscribers
  • Views 685 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Probably a stupid question...

tonydon

Right...

We are on a site with 2 onsite substations providing our supplys.

Upon inspection the supply comes from the substation transformer room, into our switch room, as a TP&N feed to our section boards.

We cant see any earth other than the armour of the supply cable which is obviously attached to the section board.

A colleague and I have been debating whether this is a TNS or TNCS supply.???

Given that the transformer is just the other side of the wall in our switch room, and that the earth and neutral must be bonded at the star point of the transformer secondary.

Are we right in thinking the supply is TNS??? 

Parents
  • 0

    if not then probably PNB.

    There are several forms of PNB (depending on which way around the earthing of the N and the N-PE split are arranged) - so still quite likely to be TN-S.

    TN-C-S can be with or without multiple earths - PME or PNB,

    PNB can be with a section of combined neutral & earth conductor (TN-C-S) or separate all the way (TN-S).

    (It gets more confusing when DNOs get involved as they often deem that "PME conditions" apply to what are actually PNB supplies, just so they can keep their options open for later conversion to TN-C-S /PME at a later date (e.g. when new consumers are added to an existing transformer)).

       - Andy.

Reply
  • 0

    if not then probably PNB.

    There are several forms of PNB (depending on which way around the earthing of the N and the N-PE split are arranged) - so still quite likely to be TN-S.

    TN-C-S can be with or without multiple earths - PME or PNB,

    PNB can be with a section of combined neutral & earth conductor (TN-C-S) or separate all the way (TN-S).

    (It gets more confusing when DNOs get involved as they often deem that "PME conditions" apply to what are actually PNB supplies, just so they can keep their options open for later conversion to TN-C-S /PME at a later date (e.g. when new consumers are added to an existing transformer)).

       - Andy.

Children
  • 0 in reply to AJJewsbury
    AJJewsbury said:

    There are several forms of PNB (depending on which way around the earthing of the N and the N-PE split are arranged) - so still quite likely to be TN-S.

    TN-C-S can be with or without multiple earths - PME or PNB,

    PNB can be with a section of combined neutral & earth conductor (TN-C-S) or separate all the way (TN-S).

    (It gets more confusing when DNOs get involved as they often deem that "PME conditions" apply to what are actually PNB supplies, just so they can keep their options open for later conversion to TN-C-S /PME at a later date (e.g. when new consumers are added to an existing transformer)).

    Just to clarify 100 % ... PME exists only in distribution systems for supply to the public, and nowhere else. The arrangements for which PME conditions apply are described in ENA Engineering Recommendation G12/4 and the ESQCR. They are TN-C-S and PNB arrangements in the public distribution network, and have to meet some specific criteria.

    If you are a private LV network with TN-C-S earthing arrangement, it is not PME. In practice, though, most (but not all) private LV networks will have separate N and PE, except upstream of the primary switchboard, if the neutral is earthed at the primary switchboard, and upstream of the main switchboard being TN-C only effectively at the transformers or generators. GN8 refers to this as a PNB arrangement.

Community Rules & Guidelines