One for the sparks

Discussion in 'Electricians' Talk' started by spen123, Jan 20, 2023.

  1. spen123

    spen123 Screwfix Select

    Evening all

    So I'm currently helping out my brother on a garage build
    Remote location but supply to house is 3 phase pme.
    No issues here.

    The garage is around 30 meters away and is of timber construction
    Plastic water feed
    No heating source.

    I'm going to export the pme to this but is does have me thinking on a few things,

    The current install has no spd so I'm thinking of installing this at the origin to cover installation
    Transformer fairly local.

    My real question comes Down to when people put systems on a tt.

    I appreciate ill be exporting the equipotential zone but don't see this as an issue unless it is?
    If someone puts a system on a tt how do they overcome the potential risk of a transient voltage?

    In remote locations that are at risk of lighting then surely a strike has the potential to to induce a transient voltage into the installation should the strike be close enough?

    Also if the cable run is long then in theory the cable acts as one large capacitor.
    No issue when the install is on but when it gets de energised you'd have the transient voltage still present and that large release of voltage could cause issues?

    I'm not sure a pme supply would counteract this but have been informed it can help to minimise this.

    Any input appreciated.
    Or being told I'm off my rocker is also appreciated haha
     
    Last edited: Jan 20, 2023
  2. Ind spark

    Ind spark Screwfix Select

    I don't see a reason to TT, no extraneous parts.
     
    spen123 likes this.
  3. spen123

    spen123 Screwfix Select

    No and even if I did i think it would be a failed one as metal electric gates are about 5 meters away so unless I could get a rid far away id just be in the pme zone
     
  4. Ind spark

    Ind spark Screwfix Select

    I done an amendment 2 ECA course the other day, they said you need to ask the DNO about the likelyhood of a PEN fault.

    They said in Wales it's more likely than in say the Midlands so each job needs to be separately assessed.
     
    spen123 likes this.
  5. spen123

    spen123 Screwfix Select

    That makes sense and will.save hopefully the installation of false tt systems
     
  6. Ind spark

    Ind spark Screwfix Select

    Always a lot to think about with TT and I don't like thinking much :D

    I'm sure the happy builder will be along soon he loves earth rod talk lol.
     
    spen123 likes this.
  7. spen123

    spen123 Screwfix Select

    Hahaha I look forward to happys input
     
  8. The Happy Builder

    The Happy Builder Screwfix Select

    What is the likelihood of this garage have PV panels on the roof, storage batteries bolted to a wall, one or two EV chargers, lots of LED lighting and a workshop with a lots of fancy kit including a flat screen TV and computers accessing social media and other things on the Internet?
     
  9. spen123

    spen123 Screwfix Select

    It will have
    Ev charging
    Tv
    Office space with computer
    Small kitchenett
    Led decorative lighting strip 20 meters
    Led workshop lighting
    Air-conditioning unit
    Welding equipment
     
  10. The Happy Builder

    The Happy Builder Screwfix Select

    I guess the SPD manufacturers will tell you to fit a Type 1 & 2 SPD at the main distribution board in the house, another Type 1 & 2 SPD in the sub distribution board in the garage and additional Type 3 SPDs within five metres of vulnerable equipment.

    https://kingsmillindustries.com/product-guide/selection-of-spds/

    I don’t know how welding equipment influences the choice and location of SPDs, if it does, but guess with the three layers of SPD protection it may not be a significant issue, I would contact a SPD manufacturer for advice.

    Regards earthing, I can’t see any particular pro’s or con’s for either choice, TT would make the EV charging installation a bit cheaper as open-PEN protection would not be required saving a few quid buying a charge point, but a three phase RCD would be required in the sub distribution board along with the rod/s.
     
  11. Bob Rathbone

    Bob Rathbone Screwfix Select

    Surely the RCD would be at the garage end, not in the supply DB. The SWA on the supply cable would be terminated at the supply end and left disconnected at the garage end, SWA would be earthed by the PME supply system.
     
  12. Bob Rathbone

    Bob Rathbone Screwfix Select

    Without a shadow of a doubt, I would not export the PME earth to the garage, it may be difficult to drive an earth rod in some places but a mat or strip could be used instead. Make the garage a TT system with the RCD in the garage, so when it trips it's easy to reset quickly.
     
  13. spen123

    spen123 Screwfix Select

    The trouble is I don't know what services are beneath me or around me.
    They have electric metal gates that are sunk into ground and from what I can see these posts are earthed.
    So if I drive in a rod I will be in the pme zone.
    The house was built about 2 years ago with a new cable so the chances of it failing are slim.
     
  14. Ind spark

    Ind spark Screwfix Select

    Why though wheres the risk?
    Wooden structure
    No extraneous parts
     
  15. Ind spark

    Ind spark Screwfix Select

    You could use a Matt e device if your really worried but the 3 phase one is expensive, just had a look £1000 at CEF
     
  16. Bob Rathbone

    Bob Rathbone Screwfix Select

    When you install an earth rod the regulations require that the resistance area of the new rod should not overlap with others, including other services. You use an earth electrode tester with the potential difference method to establish a suitable site for the new electrode. Hello Ind Spark, I agree that at the moment their is little evidence of a risk, but we are working on the information given by Spen, which may be incomplete. As installers we have a duty to our clients, to the regulations and to HSE to look a little further and consider the possibilities of future actions of the client, how the installation may evolve and the effects of time on our installation. Making the system TT is another small step for Electrician kind, but a great leap in the quest for improved safety (sorry Niel).
     
    Ind spark likes this.
  17. Ind spark

    Ind spark Screwfix Select

    I get ya Bob, if things change in the future its already TT so no worries.

    If we put a TT system in on the moon would it be a moon rod? (Sorry to early for this):p
     
  18. spen123

    spen123 Screwfix Select

    For me to install a matt would cost a fortune as its concrete pads outside.
    Trying to get a rod to the opposite side of possible local services would also be impossible.
    Finished polished floor.
    Open glue lam ceiling
    Services room in middle of garage.
    Pre ducted for cable ways
     
  19. spen123

    spen123 Screwfix Select

    I'm not sure I could sell that to them
     
  20. Ind spark

    Ind spark Screwfix Select

    No.... but in my opinion you dont need to but these chaps know more than me.
     
    spen123 likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice