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Discuss Paralleling swa 4 core to increase CCC in the Looking for Commercial Electricians? area at ElectrciansForums.co.uk.

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  1. Foxie1
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    Foxie1 New EF Member

    Location:
    Liverpool
    Business Name:
    FWF property services
    Hello fellow sparks, I have a 400 metre drum of swa xlpe 4 core x 6mm cable I need to install 8 x 230 volt x 45 amp supplies to storage units distance from DB of 40 metres down to 35 metres. I propose to pair up the cores within each cable giving me 8 x runs of 2 core 12mm cable colour sleeved at each end (Blue / Brown) and using the armouring as the earth (CPC). Are there any adverse issues or departures from BS7671 with this procedure. It is purely a minge bag trick to save me buying the correct cable And also utilizing the spare 6mm x 4 core cable Also does anybody know how to calculate the Volt drop No table for 12mm! ( calc for 10mm maybe?) Cheers Foxie1
     
  2. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    cheshire/staffordshire
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    calculate VD for 6mm then halve the result.then do a calc. for 10mm. the values should be close with the 10mm being slightly higher. use the worst. any extraneous parts in the units? what's the earthing system?and what are the units constructed from (wood,steel,concrete, etc.)? and do you really need 45A. would 40 do it?
     
  3. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

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    Northamptonshire
    Armour is inadequate for any TN system bonding purposes.
     
  4. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    that's why i asked about extraneous.
     
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  5. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    Why?
    If it's steel - copper equivalent is that of the required size from the tables of bs7671 for a copper conductor then why not?
     
  6. davesparks
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    davesparks Trusted Advisor

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    guildford
    Because the armour of a 6mm 4core won't be big enough,
     
  7. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    In this example then yes but to say it can't be used ever in a TN installation I don't understand
     
  8. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    the armour may be OK as cpc, but not as a bonding conductor
     
  9. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    If the SWA is used as a main equipotential conductor other than on a PME system it must have a copper equivalent CSA, for CSAs over 25mm², of not less than half the cross sectional area of the associated earthing conductor and not less than
    6mm² to comply with 544.1.1. If the installation is PME then the copper equivalent CSA of the SWA must comply with table 54.8.
    If the SWA is to be used as a combined CPC and main bonding conductor it must meet the requirements of both 544.1.1 and 543.1.1
    Regulation 521.5.1 permits the use of a separate protective conductor to be run in parallel with an SWA cable.
     
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  10. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Well the chances are pretty slim of the armour ever being suitable. If the copper bonding conductor required is 10mm then the steel equivalent would need to be 85mm, which would mean a 70mm three core xlpe swa.
    But then any circuit which requires a 70mm cable will almost certainly be in an installation which requires a larger bonding conductor than 10mm.
     
  11. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    Agreed Dave I'm just saying that nowhere does it say in bs7671 that armour can't be used as a bonding conductor.
    If it can be used as a cpc then it can be used as a bonding conductor. CSA of the copper equivalent needed of course. 8.5 is the figure given in gn8 for copper to steel ratio
    1.68 for aluminium
     
  12. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Take a pill I was referring to the ops cable csa.
     
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  13. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    Ouch!
     
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  14. Foxie1
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    Foxie1 New EF Member

    Location:
    Liverpool
    Business Name:
    FWF property services
    Thanks a lot for your knowledgeable input!
    The Units are of GRP construction with no extraneous parts the earthing system will be TNC, and I think the FLC is probably closer to 50 than 40 amps I would probably fit a 50 amp type C, MCB in the D/B and to be sure I would run a singles 10mm2 green and yellow cable to each unit. A couple of these feeds will need to be buried will the 10mm earth need protecting i.e. Ducted in 20mm egatube or similar to comply? The others are on surface cable tray!
     
  15. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    They won't need a separate 10.0.
     
  16. spinlondon
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    spinlondon Trusted Advisor

    Location:
    Harlow Essex
    BS7671 doesn't state what isn't allowed (the list would be endless), it states what is allowed or required.
    One of the requirements is for bonding conductors to have the equivalent conductance of a copper conductor.
     
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  17. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
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    Wilko Electrics
    Let's hope these garages don't need bonding ...
     
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