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3/036 t and e on domestic ring final

hertzal123

On conducting a condition report the rf was found to be wired in 3/036 on a b16 mcb.

Have calculated the csa of the live conductors to be about 1.9mm2.Subject to circuit

length,could I convert to 2 radials and use the OSG table for 1.5mm cable on a 16A

mcb?The circuit serves a small lounge and bedroom.Otherwise,suspect this would attract

a C2 code.

Thanks for any advice,Hz

Parents
  • 0

    what sort of fuse/breaker or rcbo is it on, and does the cable show signs of thermal distress?

    a modern rcbo will speed disconnection to a point that will to a  degree mitigate the risk of insulation damage in an earth fault. If overload is the concern, then derate the breaker in the  ratio of the expected cross-section to what you have, so perhaps 1.9/2.5 changes 32A to 25A or less.

    Unless  you need to break the ring for other reasons I'd agree with Graham, retain the ring, it is more flexible in terms of load distribution  and safer with the redundant earth paths, and saves you a breaker position at the board.

    Mike

Reply
  • 0

    what sort of fuse/breaker or rcbo is it on, and does the cable show signs of thermal distress?

    a modern rcbo will speed disconnection to a point that will to a  degree mitigate the risk of insulation damage in an earth fault. If overload is the concern, then derate the breaker in the  ratio of the expected cross-section to what you have, so perhaps 1.9/2.5 changes 32A to 25A or less.

    Unless  you need to break the ring for other reasons I'd agree with Graham, retain the ring, it is more flexible in terms of load distribution  and safer with the redundant earth paths, and saves you a breaker position at the board.

    Mike

Children
  • 0 in reply to mapj1

    Thanks for the replies so far.The circuit is on a dual rcd board.So if no sign of overloading,the circuit could attract a C3 or no code at all?

                         Hz

  • 0 in reply to hertzal123

    Quite possibly. You might make take a more stringent view if it's rented property, or change of use (tenant may not know or care about the possibility of overload, or new owner/occupier may not be aware), but if it's an owner-occupied property, and the owner is aware of the situation, it's far less likely to be accidentally overloaded if serving a number of rooms.

  • 0 in reply to gkenyon

    Apparently 3/.036 was commonly used for immersion heater circuits. Did we every find a damaged earthing continuity conductor?

    https://www.diynot.com/diy/threads/imperial-cable.214429/#:~:text=As%20per%20the%20table%2C%203%2F.036%20had%20a%201%2F.044,inbuilt%20core%20must%20be%20very%20rare%20Not%20especially.

    Don't be shy chaps - pros will know...

    3/0.029" x 1/0.044" (cpc 0.98mm²)
    3/0.036" x 1/0.044" (cpc 0.98mm²)

    7/0.029" x 3/0.036" (cpc 1.97mm²)

    7/0.036" x 7/0.029" (cpc 2.98mm²)

    7/0.044" x 7/0.036" (cpc 4.59mm²)

    7/0.052" x 7/0.044" (cpc 6.86mm²)

    7/0.064" x 7/0.052" (cpc 9.59mm²)

    Apart from final two, have measured real cable with trusty Moore & Wright.
    -0-

    Z.

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