Current ratings for 7.035?

Discussion in 'Electricians' Talk' started by 14th edition, Dec 29, 2009.

  1. 14th edition

    14th edition Well-Known Member

    Hi,
    Hoping to extend a radial circuit wired in [I think!] 7.036 t/e but wasn't sure what the rating of it was. I think its broadly the same as 4mm.
    It looks like this 70's house was wired in radials and at some point someone had stuffed three 7.036's into one 32a mcb to create a little space. No spare ways, got to provide for 2KW underfloor heating!

    Cheers,

    14th
     
  2. lamps

    lamps New Member

    whats the cpc size
     
  3. 14th edition

    14th edition Well-Known Member

    Not sure on cpc size!
     
  4. lamps

    lamps New Member

    be carefull here you might need to downgrade breaker due to inadequate cpc. then you could have nuisance tripping have you laid flooring?
     
  5. 14th edition

    14th edition Well-Known Member

    Nope, made the mistake of taking socket off adjacent to new conservatory, seeing two pairs and assuming ring main!!Tested for continuity and sweet FA on anything.Asuming radials at present, testing am tommorrow.
    Whats the issue with CPC size? I can replace with a 16a breaker no probs, kitchen and extension are on separate rings[much more recent stuff].

    Cheers

    14th
     
  6. lamps

    lamps New Member

    7.036 can have a breaker up to 31a so as soon as you alter that ctt your responsible well liable
    no spare ways little options here maybe an add on?
     
  7. 14th edition

    14th edition Well-Known Member

    Hi Lamps,
    Cheers for help, may move another cicuit at DB to create one extra for 7035 and derate to 16a.

    Cheers,
    14th
     
  8. lamps

    lamps New Member

    dont touch ctt m8. if it starts tripping your phone will start ringing, advise them and price it up the freebies always get you
     
  9. 14th edition

    14th edition Well-Known Member

    Why should it start tripping?

    14th
     
  10. lamps

    lamps New Member

    well if its 32a now you downgrade to a 16 its liable to trip due to loading
     
  11. pcelectrics

    pcelectrics New Member

    7/.029 has a csa of 3.0mm and an individual strand diameter of 0.74mm (measure with a vernier caliper to confirm size). It is rated at 31A on an MCB or cartridge fuse.

    7/.036 has a csa of 4.6mm and an individual strand diameter of 0.91mm (measure with a vernier caliper to confirm size). It is rated at 41A on an MCB or cartridge fuse.

    CPCs could be either 1/.044 =1.0mm csa & 1.12mm strand diameter, 3/.029 =1.3mm csa or 3/.036 =2.0mm csa. Do the adiabatic to confirm cpc size adequacy for MCB ratings once you know the cpc size. Without performing the calcs myself just now, IIRC these 3 strand cpcs are good for 32 and 40A MCBs respectively.

    This info comes from a scan I have of the relevant ratings table from the 1966 issue of the wiring regs (14th edition I think).
     
  12. 14th edition

    14th edition Well-Known Member

    Ah, sorry thought you meant RCD! New heating will be 1.8kw, say 8-9 amps. No other real load on same circuits.

    14th
     
  13. lamps

    lamps New Member

    so if you go to a 20a your fine
     
  14. 14th edition

    14th edition Well-Known Member

    PCelectrics,
    Must be 1044 as it is single strand, unless it is 7029...But it looks too chunky for that. I don't possess a vernier!

    14th
     
  15. pcelectrics

    pcelectrics New Member

  16. dont know much

    dont know much New Member

    14th Edition 7/036" did have a cpc of 3/029" same size as 7/029" 1/044 was only used as the cpc in 3/029" my
    source of reference is the 14th edition light blue cover dated 1966 was ammended to 14th edition metric cables in 1970 orange cover
     

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