Posting a message to the forum will remove the above advertisement
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  2. angel While you're here, would you mind checking out our Electrician's Insurance section to see if we could save you a few quid? - Specifically our Van Insurance Deals and Public Liability Insurance Deals. Thanks for supporting the forum! angel

    5% Discount from Electrical2Go.co.uk for ALL members! - Click Here

Discuss TT Distribution Best Practice in the Electrical Wiring, Theories and Regulations area at ElectrciansForums.co.uk.

Thread Status:
Not open for further replies.
Please make sure you checkout our forum sponsors, many do discounts for members and, they keep the forum free to use.
  1. owenskinner
    Offline

    owenskinner Active EF Member

    Hi all.

    New to this place and have a question about TT distribution.

    New 80A TT Supply being put in.
    Have to send it 45m to a new Barn Conversion but am unsure best practice.
    I am going to put a time delayed 100mA RCD by the Main fuse and then get a consumer unit with 30mA standard type RCD at the Barn Conversion.

    Is there any need to protect it for overload and short circuit? As I understand it anything more than 3 Metres from the DNO fuse then it needs to be fused. If so is a High current (80A) MCB sufficient or should an HRC be used?

    I was thinking of using a double pole 80A 100mA RCBO, but no one seems to make them (RCBO) with a higher current rating than 40A (Or do they????).

    This led me down the path of Wylex 4 Way Metal Clad Panel (Compare Wylex ESM8 Wylex Enclosure Kent Products), 100A 100mA time delayed RCD and then Doube Pole 80A MCB (High Current MCB Double Pole 80A - High Current MCB Double Pole 80 Amp - High Current MCBs Double Pole - High Current MCBs 63 Amp To 125 Amp - Expert Electrical).

    Am I being belt and braces or is this the best way to go?

    Any neater, solutions more than welcome.
     
  2. telectrix
    Offline

    telectrix Scouser and Proud of It Trusted Advisor

    Top Poster Of Month

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    the cable to the barn needs OCPD . 80A switch fuse is the norm, but nothing wrong with an 80A MCB.
     
  3. owenskinner
    Offline

    owenskinner Active EF Member

    Thanks Telectrix. Is 'OCPD' Over Current Protective Device? Not used to the abbreviations..
     
  4. NMc
    Offline

    NMc Electrician's Arms

    You are doing a barn conversion 45m from an existing supply and taking 80A off that supply. Are you sure that the existing will take the additional load?
     
  5. High Tower
    Offline

    High Tower Trusted Advisor

    Location:
    Birmingham
    If you fit a 100mA rcd then you will also need to rcd near enough all of the circuits so you may as well just forget that and install a standard dual 30mA rcd board
     
  6. owenskinner
    Offline

    owenskinner Active EF Member

    It is a new supply for the Barn Conversion so has no other load. I did recommend to the client to have the new supply put in straight to the Barn but he didn't want his driveway (mud and a few cobble stones) dug up! I have done the cable calcs and it came up with 35mm so I am putting in 2 Core 35mm SWA buried 600mm down.
     
  7. owenskinner
    Offline

    owenskinner Active EF Member

    Surely the distribution SWA cable needs RCD protection also. 100mA time delayed RCD at the beginning for discrimination, 30mA at the Barn end also.
     
  8. High Tower
    Offline

    High Tower Trusted Advisor

    Location:
    Birmingham
    Why would you need to rcd a earthed SWA??? And what would you need the 100mA for if the circuits have 30mA protection as per regs
     
  9. owenskinner
    Offline

    owenskinner Active EF Member

    In case someone puts a shovel through the distribution cable I presume?
     
  10. NMc
    Offline

    NMc Electrician's Arms

    I thought under the ElectricitySafety, Quality and Continuity Regulations (ESQCR) 2002 all new supplies had to have an earth provided?
     
  11. Heisenberg
    Offline

    Heisenberg Regular EF Member

    Location:
    London
    No, the DNO is only obliged to maintain the upkeep of an existing earth, they are not required to provide one if one does not already exist.

    EDIT: Obviously if they are supplying a PME then that's a different matter.
     
    Last edited: Feb 23, 2012
  12. NMc
    Offline

    NMc Electrician's Arms

    I agree with the fact that if the supply does not have an existing earth provided then it is up to the used of the supply. But somewhere along the line I have picked up that new supplies are different that is why DNO are putting PME in
     
  13. Jimmyb
    Offline

    Jimmyb Electrician's Arms

    Location:
    East Yorkshire
    do you really have to rcd the swa ?
     
  14. MarkRibbands
    Offline

    MarkRibbands Regular EF Member

    Location:
    Malaysia and UK
    Yes, I'm puzzled too. Surely there's no need to RCD protect a 35mm SWA distribution circuit properly buried 600mm under the ground?

    Just a normal switchfuse will do the job. Personally I'd try to get one with a big box to make directly terminating that 35mm easier! Is it single phase only?

    BTW, is there no chance of getting PME?
     
    Last edited: Feb 24, 2012
  15. spinlondon
    Offline

    spinlondon Trusted Advisor

    Location:
    Harlow Essex
    No it doesn't require RCD protection, if the Ra of the earth electrode is sufficiently low enough to allow the OCPD to operate.
    However, as that is probably not going to be the case, then an RCD is the only option to achieve the required disconnection times (1s for TT distribution circuits).
     
    • Like Like x 4
Loading...
Similar Threads - Distribution Best Practice Forum Date
Are there any TT LV wooden pole monkey power distribution sparks on this forum ? Electrical Forum Saturday at 1:11 AM
TV distribution for block of flats FreeSat, Sky, VirginMedia Forum Jun 1, 2018
Thread Status:
Not open for further replies.

Share This Page

Electricians Directory Post a Domestic Job Post a Commercial Job