who downrates 32a mcb to 20a for ring mains when cables under more than 100mm of loft insulation ?

Discussion in 'Electricians' Talk' started by ram, Dec 4, 2017.

  1. ram

    ram Member

    who downrates 32a mcb to 20a for ring mains when cables under more than 100mm of loft insulation ?
     
  2. Dr Bodgit

    Dr Bodgit Well-Known Member

    I doubt anyone would as the current going through such cables is almost never going to be towards the upper limit, it may peak for a short period of time.
     
  3. ram

    ram Member

    nic tech helpline just said it has to be down rated... so many different opinions on this stuff
     
  4. Dr Bodgit

    Dr Bodgit Well-Known Member

    Technically yes, but apply some common sense to the situation.
     
  5. JP.

    JP. Screwfix Select

    Is that your missus in your profile pic Doc?
     
  6. Dr Bodgit

    Dr Bodgit Well-Known Member

  7. JP.

    JP. Screwfix Select

    Right - nice one Doc
     
  8. unphased

    unphased Screwfix Select

    The ring circuit is a standard circuit so design derating factors are already taken in to consideration. If the NICEIC are insisting on you doing it, get it in writing. I'll bet a pound to a penny they wont do that. Madness, absolute madness.
     
  9. Sparkielev

    Sparkielev Well-Known Member

    Nic think they own the electrical world, bunch of bumbling buffoons
     
  10. nigel willson

    nigel willson Well-Known Member

    Try this one! What’s a RING MAIN???
     
  11. Bazza-spark

    Bazza-spark Well-Known Member

    OMG ring circuit not ring final. HORROR !!!!! :D:D:D;););) lol
     
  12. leesparkykent

    leesparkykent Well-Known Member

    A ring final circuit wired in 2.5mm T&E meets the requirements of reg 433.1.1 if the current carrying capacity of the cable is not less than 20A. If the cable is installed reference method 101 then iirc the CCC is about 17A. A standard ring final circuit is based on a design current of 26A...20A at its furthest point and the remainder up to the rating of the over current protective device evenly distributed. The standard circuit design of the ring final circuit does not take installation method in to account. You have to take the installation method into account when designing the circuit.

    The NICEIC were correct that if the cables CCC was not capable of handling a current of 20A when installation method has been taken into account then the OCPD should be changed.
     
    Last edited: Dec 4, 2017
  13. leesparkykent

    leesparkykent Well-Known Member

    It's a design of circuit used in HV distribution.
     
  14. Bazza-spark

    Bazza-spark Well-Known Member

    What a load of rubbish!

    The IET change the rules to suit themselves.

    Circuts installed in the 70's and 80's complied with the Regs at the time. The fact people have thrown 3 tons of insulation over the cables doesn't alter the fact the circuits are working and the insulators never told the occupants "you will need to have your place rewired with huge cables" didn't come into it.

    The cables are still capable and the circuits are still fine.
     
    Dr Bodgit likes this.
  15. leesparkykent

    leesparkykent Well-Known Member

    No it's not rubbish....Its in black and white for you to read. Regulation 433.1.1 is satisfied if the cable has a current carrying capacity of not less than 20A. If installed reference method 101 the current carrying capacity of the 2.5 T&E is less than 20A. You may think it's a load of rubbish but it doesn't change the fact that the cable has a current carrying capacity of less than 20A which does not satisfy the regulations based on a Ring final circuit protected by a 30A or 32A over current protective device.
     
  16. Bazza-spark

    Bazza-spark Well-Known Member

    So when you are carrying out what was known as a periodic inspection, but is now an electrical conditon report, do you condemn installations that have had loft insulation thrown over the cables?
     
  17. leesparkykent

    leesparkykent Well-Known Member

    I would code it appropriately.
     
  18. leesparkykent

    leesparkykent Well-Known Member

    And BTW, you still carry out periodic inspection and testing you just produce/issue an electrical installation condition report.
     
    Risteard likes this.
  19. Bazza-spark

    Bazza-spark Well-Known Member

    :rolleyes:
     
  20. Bazza-spark

    Bazza-spark Well-Known Member

    Just wanted you to understand the difference in terms because I'm not sure you understand the difference in regulation requirements/
     

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