Extending Wiring behind Plug Socket

Discussion in 'Electricians' Talk' started by reepers, Jul 20, 2015.

  1. FatHands

    FatHands Well-Known Member

    Sen / Spin,
    Can you clarify the current rating for the connectors?
    thanks, fats (likes learning from the wise owls)
     
  2. seneca

    seneca Screwfix Select

    That would be the case with the aluminium cables that were used for a while in the '70's but it's not a problem with copper Dave.
     
  3. seneca

    seneca Screwfix Select

    15/16 amps is sufficient for a ring circuit, each leg only carries half the load.
     
    FatHands likes this.
  4. reepers

    reepers New Member

    All fitted, used blocks and leccy taped em. Was fine in a 25mm box, works brill too. Thanks to everyone on this thread :)
     
  5. FatHands

    FatHands Well-Known Member

    hi sen,
    i had this back from wago some time ago when i asked them about their connectors on a ring which is why i questioned it mate:

    The section in the installation requirements (BS 7671) that deals with ring final circuit in BS7671 is 433.1.103 where the relevant text says: "Such circuits are deemed to meet the requirements 433.1.1 if the current carrying capacity of the cable is not less than 20A and if under the intended conditions of use the load current in any part of the circuit is unlikely to exceed for long periods the current carrying capacity of the cable."
     
    eric the fish likes this.
  6. Coloumb

    Coloumb Screwfix Select

    I've never really understood it either but I would prefere a good tight connection with a 15 block than a 30 a block. I don't think the rating of the block has a lot to do with anything anyway since the copper/brass used in the block looks to be much bigger csa than the cable.
     
  7. FatHands

    FatHands Well-Known Member

    Good point Col. i heard some sparks say not to use 20a dp isolators on rings for the same reason and know others who say its nonsense!
     
  8. seneca

    seneca Screwfix Select

    Agreed and also of course the cable will be quite a long length compared with the half an inch of brass in the connector!
     
  9. peter palmer

    peter palmer Screwfix Select

    seneca makes a good point, its all to do with length, look how thin a piece of 30A fuse wire is yet it sits there quite hapily because its only a couple of inches long, try to wire a ring with it and it would be a different story.
     
    FatHands and seneca like this.
  10. spinlondon

    spinlondon Screwfix Select

    Unfortunately such a situation where each leg carries half the load, only occurs when the load is connected at the mid point of the ring.
    Where the load is connected at any other point on the ring the load on each leg is proportional according to where on the ring the load is connected.
    A 20A load connected a quarter way round the ring would entail that the short leg carries 15A and the long leg 5A.
    Remember, V = I x R.
    The lower the resistance the greater the amperage.
    The higher the resistance, the lower the amperage.
    Generally, when constructing a ring, the equipment has a minimu current carrying capacity two thirds of that of the rating of the overcurrent protection.
     
  11. seneca

    seneca Screwfix Select

    Yes I agree with your theory explanation Spin but for all practical purposes we can assume that each leg will be carrying half the load current, in any case how many domestic rings will be running at full capacity. Text book theory is all very well but day to day in the real world we can't always do things quite "by the book"!
     
  12. Risteard

    Risteard Screwfix Select

    Technically however each leg must be capable of carrying 20A, as the load will not split evenly unless we had the load right at the midpoint of the ring without other loads present.
     
  13. Risteard

    Risteard Screwfix Select

    Oh, I see spinlondon got there first.
     
  14. Risteard

    Risteard Screwfix Select

    The cable only has to be able to carry 20A, so no reason to hold a switch to a greater standard.
     
    FatHands likes this.
  15. Risteard

    Risteard Screwfix Select

    It sits there because it is not covered with insulation etc. so can dissipate heat to a much greater extent. It isn't the length of it which causes it to work as a fuse.
     
    FatHands likes this.
  16. peter palmer

    peter palmer Screwfix Select

    You could put 6" of 1mm in a ring main and it would run at the full capacity of 32A all day long without ever getting warm. However if you wired the whole ring main out of 1mm then you would have problems. A short length of something that is underrated will not be a problem, it may not say so in the precious regs book but in the real world its fine.
     
  17. seneca

    seneca Screwfix Select

    No point in mentioning "the real world" Peter, some of them don't know it exists but others of us actually work in it!
     
  18. Risteard

    Risteard Screwfix Select

    It would get warm actually. The difference is that a fuse can dissipate heat far more readily.

    How do you claim that after a length of time 1mm^2 would not get hot with a constant 32A load regardless of its length?
     
  19. Rulland

    Rulland Screwfix Select

    Peter actually said there would be problems with a long length.
     
  20. Risteard

    Risteard Screwfix Select

    But a short length will still get warm. How does he believe that it wouldn't?
     

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