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 24 replies
  • Subscribers 32 subscribers
  • Views 4562 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

Metal - clad buildings and the confused forum member.

UKPN
One of the members has queried ESQCR bonding/earthing PME requirements for the above. So its worth spending a little time putting across the companies requirements. Where metal-clad buildings incorporate a steel-frame that utilises steel vertical beams that are within the foundations, the steel frame will provide a good connection with the earth which will effectively limit the earth potential rise.

A PME service may be provided to a metal-clad building provided the following criteria are satisfied:


1. The metal cladding is bonded to the steel-frame.

2. The supply is either three-phase with less than 40% unbalance or the supply is single - phase and the frame to earth impedance is les than 20ohms.

Regards, UKPN?

Parents
  • 0
    The importance of this relates to Regulation 442.2.1 (in this case, if you are one of the TT consumers, you are having to rely on an additional earth electrode in someone else's installation - so how can the designer ensure BS 7671 is complied with)

    As I see it, if it was a pure TT system there wouldn't be an issue (Uf would be zero). The problem comes from the influence of the PME earthing system supplying another unit - but that PME earth itself presumably satisfies the requirements of 442.2.1 (presumably by some approximation to a 'global earthing system') - so I'm thinking that if the PME earth in the other unit is deemed safe, then it's influence in our TT unit can't be any more dangerous.

     
    the effectiveness of the chosen method of connection of surge protection

    Being our unit is TT, SPD would either be connected CT2 before the first tier of RCDs (CT1 not permitted in that position for TT) or CT1 or CT2 afterwards. As I understand it both CT1 and CT2 are acceptable on TN installations in both positions - so if our TT installation behaves more like a TN one, I don't see a problem. (Although I can see a potential problem the other way around - if we had CT1 connections pre-RCD and the installation somehow behaved more like TT one.)

     
    potentially the insulation coordination of switchgear etc

    Again the worst case would seem to be for the TT installation (voltage between live parts and exposed-conductive-parts reaching RE x IE + U0 as the local rod holds exposed-conductive-parts close to true Earth while N and line conductors are raised by the HV earth fault) so switchgear designed for a TT installation should if anything have an easier life if the installation behaves more like a TN one.


       - Andy.
Reply
  • 0
    The importance of this relates to Regulation 442.2.1 (in this case, if you are one of the TT consumers, you are having to rely on an additional earth electrode in someone else's installation - so how can the designer ensure BS 7671 is complied with)

    As I see it, if it was a pure TT system there wouldn't be an issue (Uf would be zero). The problem comes from the influence of the PME earthing system supplying another unit - but that PME earth itself presumably satisfies the requirements of 442.2.1 (presumably by some approximation to a 'global earthing system') - so I'm thinking that if the PME earth in the other unit is deemed safe, then it's influence in our TT unit can't be any more dangerous.

     
    the effectiveness of the chosen method of connection of surge protection

    Being our unit is TT, SPD would either be connected CT2 before the first tier of RCDs (CT1 not permitted in that position for TT) or CT1 or CT2 afterwards. As I understand it both CT1 and CT2 are acceptable on TN installations in both positions - so if our TT installation behaves more like a TN one, I don't see a problem. (Although I can see a potential problem the other way around - if we had CT1 connections pre-RCD and the installation somehow behaved more like TT one.)

     
    potentially the insulation coordination of switchgear etc

    Again the worst case would seem to be for the TT installation (voltage between live parts and exposed-conductive-parts reaching RE x IE + U0 as the local rod holds exposed-conductive-parts close to true Earth while N and line conductors are raised by the HV earth fault) so switchgear designed for a TT installation should if anything have an easier life if the installation behaves more like a TN one.


       - Andy.
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