Radial circuit and cable thickness

Discussion in 'Electricians' Talk' started by nigelf, Nov 16, 2009.

  1. nigelf

    nigelf New Member


    I have been reading a little, which is probably my first mistake, and I have picked up on the fact that a radial circuit with 20A breaker can have 2.5mm2 cable, but a 32A radial circuit needs 4.0mm2, while a 32A ring maing only requires 2.5mm2.

    Can anyone explain this in plain english?

    I want to run a tumble drier, plinth heater, Dishwasher and washing machine off this radial circuit, which is governed currently by a 16A MCB and presumably 2.5mm2 cable
  2. seneca2

    seneca2 New Member

    while a 32A ring maing only requires 2.5mm2.

    Can anyone explain this in plain english?
    That's because a ring circuit is effectively two 2.5mm cables in parallel.
  3. JP.

    JP. Screwfix Select

    Must say the 16 Amp is a tad limiting.
  4. JP.

    JP. Screwfix Select

    Just goes to prove that the (post war designed due to copper shortage) Ring Finals will never be beaten.

  5. nigelf

    nigelf New Member

    Yes it is - I was hoping to upgrade it to a 32A mcb, but I think, given another response, that the cable will be the limiting factor and will not be safe running the 4 items. It may be worth routing a proper sized cable to where I need it....

    Thanks for your input.
  6. nigelf

    nigelf New Member

    Thanks seneca2, that was plain enough!
  7. JP.

    JP. Screwfix Select

    Well at the end of the day if that radial in the kitchen is 2.5mm then subject to tests and stuff you could whip in a 20 Amp MCB. I mean has it got RCD protection and stuff Nige?

    Whats the loop reading on the last socket?
  8. JP.

    JP. Screwfix Select

    Will it trip?

    Answer..now and then, but probably not much..not good design really.
  9. bluevelvet

    bluevelvet New Member

    Nige- what they haven`t explained is: the reason for a 20A MCB on a 2.5mm radial is because the 2.5mm cable in the best situation is only rated at 27A
  10. sparky308

    sparky308 New Member

    You can keep your ring finals. I'm doing all new kitchens with two 4mm radials on 32A breakers now. For a full rewire, I put the other rooms each on a 2.5mm, 20A radial. Much quicker to test and easier in the consumer unit too. Rings are just a waste of time, literally so when you have to fault-find.
  11. yorkie09

    yorkie09 New Member

    To Sparky308,
    do U put radial in each bedroom, tv room on their own 2.5mm 20 Amp radial? I have just done a rewire with ring mains for downstairs, kitchen and upstairs but that was the way I was taught! I am seriously considering radial for my next rewire?!
  12. Accaman

    Accaman New Member

    Depends on size of house but i have a 4mm radial upstairs,4mm down,and a 4mm kitchen radial.But i did get a job lot of 4mm T & E the other day...;)
  13. the sparks

    the sparks New Member

    Ring circuits had some major advantages after the war, as they saved copper and installation time and other materials, by reducing the typical domestic installation from multiple radial circuits to only 3 circuits in total (generally, one cooker cct, one ring and one ltg circuit).

    nowadays, things have changed and we generally use at least three rings per house now, plus radials and multiple lighting circuits so the copper advantage isn't really there anymore.

    In my opinion, rings lead themselves to potential problems...mistakes are easy to make (although an experienced sparky shouldn't make them), testing takes longer, a lack of design can lead to poor load distribution, faults are common and are generally not noticed without testing. In comparison to a broken ring circuit, which presents a danger, a broken radial will not necessarily be dangerous and it will also be spotted because something wont work.

    Ok, rings do have some advantages, they can be used effectively to reduce voltage drop on large circuits (such as external car park lighting and cleaner's ring circuits...), used in the right application they can reduce cable usage and fewer protective devices, plus they are useful in fulfilling high integrity earthing requirements...but I do think rings have had their place in the domestic environment, where there is a higher possibility of un-skilled alterations.

    Possibly with the exception of kitchens, I would say that 2.5mm 20A radials would be more than adequate for a house.
  14. lamps

    lamps New Member

    acca some geezer julius needs your expertise
  15. Jumpingjack232

    Jumpingjack232 New Member

    Radials are the way forward, think european!! Only grief is terminating the 4mm if you go down the 32a route.
  16. Accaman

    Accaman New Member

  17. cliffy brown

    cliffy brown New Member

    its alright steve, i've put him right
  18. seneca2

    seneca2 New Member

    Radials are the way forward, think european!!
    We've got enough **** and grief from Europe here already without adopting their wiring systems as well!
  19. the sparks

    the sparks New Member

    well they're unlikely to adopt the ring circuit!
  20. seneca2

    seneca2 New Member

    Admin are on the ball tonight, they edited my 'carp' immediately!

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