Minimum earth size for 16mm T&E submain.

Discussion in 'Electricians' Talk' started by peter palmer, Apr 4, 2016.

  1. peter palmer

    peter palmer Super Member

    Just doing a periodic on some offices, and each office has a small mains unit fed with a piece of 16mm t&e, they are relying on the 6mm earth in the cable for the main earth. Now they are only a few sockets and lights in each office, no bonding needed or anything and if you do the aidiabatic equation the size is well in but I'm not 100% sure whether to code it on the report or not.

    There are individual isolators for each submain and these are fed with 25/16 earth tails so that covers the main earth cable size.

    This is the distibution area by the way, the real problem is the whole lot is fed from a single 100A supply, this wouldn't be too bad but there is a chip shop wired off it as well. Cut out too hot to touch pulling 75+ amps.

    dis area.jpg
     
  2. spinlondon

    spinlondon Screwfix Select

    Can't see anything wrong with the T&E earth.
    You say that the cut out is too hot to touch even though it is 100A and only pulling 75A.
    I would attempt to verify that it is a 100A supply.
     
    madhatter1uk likes this.
  3. peter palmer

    peter palmer Super Member

    Not the best picture.

    fuse.jpg

    Thought it was 3 phase at first glance, lead incoming cable with 100A fuse, the other two are unused but look like they are connected with a bus bar through them, I suppose the load could be split between them but you would still have a single neutral return and obviously the same load is still on the lead cable. Earth connection is **** as well.

    Meant to add, its probably my clamp meter that inaccurate, although the live is warmer than neutral so possibly bad connection.
     
  4. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    16mm Twin and skin will be sized accordingly to the adiabatic

    Tis all ok
     
  5. Risteard

    Risteard Well-Known Member

    It can't be as this varies based upon a number of factors which require calculation, so is different for every installation. T&E is essentially designed to be used with domestic installations only.

    That said, if we are being told that the cpc size does satisfy the adiabatic equation then I can't see why we are being asked if the cpc size is adequate. Surely he has answered his own question.
     
    leesparkykent and sparky Si-Fi like this.
  6. JP.

    JP. Screwfix Select

    Never relied on the 16mm t + e cpc when we did conversions. I always ran a separate 10mm green/yellow to each flats earth marshall from intake position.

    All labelled accordingly.
     
    sparky Si-Fi likes this.
  7. unphased

    unphased Screwfix Select

    If the cut-out is "too hot to touch" does that not raise any alarm bells? Like a potential fire? All that f lot on one cut out? I would say that far exceeds the concern over a bloody cpc wouldn't you?
     
    sparky Si-Fi likes this.
  8. peter palmer

    peter palmer Super Member

    Its a report not a fix it, I have to mention everything and I'm pretty sure I already know the answer to the hot fuse.
     
    Lectrician and Mr Me-e like this.
  9. JP.

    JP. Screwfix Select

    We had running pitch on a cutout - the fuse contacts were arcing, dno changed everything foc.
     
    Last edited: Apr 5, 2016
  10. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    I was referring to 16 mill Twin and skin on domestic, why would you use it on Industrial..??
     
  11. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    Good practice JP that all sparks should do
     
  12. Risteard

    Risteard Well-Known Member

    You shouldn't, but you see all kinds of crazy things these days. The OP did tell us that these were offices - not a domestic installation.

    But the adequacy of the cpc can only be confirmed by calculation, which the OP tells us he has done. So I don't understand why he thinks an observation would be justified on a report when he has confirmed that the cpc is of an adequate csa.
     
    sparky Si-Fi likes this.
  13. nffc

    nffc Active Member

    Where does anywhere state you should not use T&E on industrial work?
     
  14. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    I would not use Twin and skin on any Industrial install, see it loads of times tie wrapped to tray etc.
     
  15. Risteard

    Risteard Well-Known Member

    T&E is designed for domestic work only, so its use elsewhere is rough and should be discouraged.
     
  16. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    With you on that Risteard, I too have seen it lashed up on anything. .
     
    Risteard likes this.
  17. nffc

    nffc Active Member

    Now I never said I would use it. You have both made claims it is designed for domestic only. Can you back this up as I have never heard this before?
     
  18. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    Twin and skin sheath does not have the same mechanical protection as say SWA or conduit etc. so its not best suited to industrial works
     
  19. nffc

    nffc Active Member

    Ahhh but you never said that did you. You agreed with Risteard that it is 'not designed for industrial use'. If this statement is true then in the ops case cable is being used against manufacturers guidance which is a reg break and should be coded.

    Of course, however T&E is not specifically designed for any particular sector so that statement is rubbish.
     
  20. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    I did not mention the mech. protection as I thought you would know this being a spark.
     

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