Need help choosing a mains supply cable

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  • Thys LOW Elektries
    Silver Member

    • Jan 2021
    • 269

    #1

    Need help choosing a mains supply cable

    Good day, I need to take the main supply cable from the main DB to a sub-DB The route is mostly on a cable tray in a ceiling void and through a service shaft.
    SWA cable is heavy, bend difficult and I don't need the armoring of the cable.
    I want to use something like Surfix but the Engineer disagree since the earth is too thin. He wants me to bring in an extra earth with the Surfix!?
    I can't get a 10mm 3c+e Surfix, if there was one it would have worked 100%

    I'm now thinking of using Airdac, can I?

    Greetings
  • GCE
    Platinum Member

    • Jun 2017
    • 1472

    #2
    Originally posted by Thys LOW Elektries
    Good day, I need to take the main supply cable from the main DB to a sub-DB The route is mostly on a cable tray in a ceiling void and through a service shaft.
    SWA cable is heavy, bend difficult and I don't need the armoring of the cable.
    I want to use something like Surfix but the Engineer disagree since the earth is too thin. He wants me to bring in an extra earth with the Surfix!?
    I can't get a 10mm 3c+e Surfix, if there was one it would have worked 100%

    I'm now thinking of using Airdac, can I?

    Greetings
    Is it single phase supply ?
    If so then you can use airdac but it must be concentric and split neutral
    Often the municipalities use the airdac that does not have a split neutral - that one you cannot use

    6.2.13 Single-phase concentric cables for aerial service connections
    6.2.13.1 Concentric and split concentric cables are single-phase XLPE
    insulated copper cables available in sizes 4 mm2, 10 mm2 and 16 mm2 and
    are designed for aerial application, but may also be used underground. These
    cables are primarily used for the provision of an electricity supply from a
    distribution main or aerial bundled conductor (ABC) system to individual
    houses. For current ratings, see table 6.20.
    6.2.13.2 Split concentric cables are provided with an integral earthing
    conductor and can be used in single-phase circuits in an electrical installation.

    6.2.13.3 Concentric cables only contain a phase and concentric conductor to
    be used in combined neutral earth systems which does not make it suitable
    for circuits in an electrical installation except where a separate earthing
    conductor is installed.



    I assume the consultant is against the surfix because the earth is not the same size as the phase conductor - Unfortunately they have not read and understood 6.12.1.1 b
    They manufacturers rate the earth wire based on the calculated allowed current in the phase wire as stipulated in there data sheets - Surface area etc comes into play which is why it is worded as such.
    Had a long argument with a consultant over ECC cable and the earth sizes - I just kept referring him back to the reg.


    6.12.1 Earth continuity conductors
    6.12.1.1 An earth continuity conductor shall
    a) consist of compatible conductors,
    b) if it forms part of a cable other than a flexible cable, comply with the relevant
    requirements of the standard for the cable,
    c) if it forms part of a flexible cable, be of the same material as, and have a
    nominal cross-sectional area at least equal to, that of the largest phase
    conductor,
    d) be able to carry the prospective fault current without excessive temperature
    rise of the conductor, within the disconnecting time,
    e) if it does not form part of a cable or flexible cable, have a nominal
    cross-sectional area in accordance with table 6.25 applied in conjunction
    with table 6.28(b) and the length to be determined in accordance with
    table 6.28(a) or 6.28(b) or calculated, as follows:

    Comment

    • Thys LOW Elektries
      Silver Member

      • Jan 2021
      • 269

      #3
      Thanks. Yes, it is single phase. Two major concerns with Airdac are the confusion about the two types and whether it will overheat or not in the ceiling.
      But I lean towards using Airdac or Surfix
      Never worked on a building of this magnitude and have to help engineer setting up a data pack for BOQ and quotations.
      Nice work though

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