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Discuss 16mm tails with 100A fuse ??? in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Job today to change out old fusebox and I'd noted the 16mm tails but on pulling the fuse this morning it was 100A which I wasn't expecting. Fairly recent new smart meter installed by XYZ who are also the DNO ... Shouldn't the fuse be limited to 60A in this case? Thoughts and advice appreciated :)
     
  2. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Could you not change them to 25.0
     
  3. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    As it's existing are you expecting that your total demand is going to be higher than the rated CCC of the tails ?
    16mm tails are good for 87amps clipped direct
     
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  4. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    What are they rated at once you enclose them in CU as they are no longer clipped direct and should be derated.
     
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  5. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    WEve had this argument before.
    Then by definition nothing can be classed as clipped direct as it ultimately terminates into an enclosure
     
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  6. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Between meters and service terminal blocks they are, as soon as you contain them they are no longer clipped direct throughout and that rating will not apply.
     
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  7. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    Rubbish!
     
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  8. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Is it, justify clipped direct when it is partially contained.
     
  9. Rpa07
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    Rpa07 2000 posts - only 46379 behind Telectrix! Electrician's Arms

    Location:
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    Ebenezer electrical
    Do you really think that Westy, really or is there some pedantry going on- you've brought it up in the past?
     
  10. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    Its all about how the cable is installed and it's ability to dissipate heat.
    Sorry but that's just another post meant quite frankly to annoy people
     
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  11. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Back on track - how difficult would it be to change the tails?

    What do you estimate the maximum load to be for the property? If its well under 87 amps you could reasonably leave the 16mm in place ....

    tin hat is on!
     
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  12. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Quite the opposite it is a reasoned argument using as you say, how the cable is installed and it's ability to dissipate heat whereby this ability is lowered once contained.
     
  13. Des 56
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    Des 56 Trusted Advisor

    Location:
    Gliese 581C
    If a cable passed directly through a insulation packed 4x2 stud partition so that those few inches were all that was not clipped direct,how many of you would de rate the cable?
    Getting rid of that heat is what the ccc are all about as Ian mentioned previously
     
  14. Rpa07
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    Rpa07 2000 posts - only 46379 behind Telectrix! Electrician's Arms

    Location:
    Bristol
    Business Name:
    Ebenezer electrical
    Maybe we shouldn't be IP rating the CUs then - let the wind flow free! Or fit a permanently running CPU fan!
     
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  15. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Well, I did try to move the tails but only got the 20cm I needed for the new CU and they won't budge any more, although there is slack at the meter. So changing the tails will be mission messy. Tails leave the external chest high meterbox in a cavity brick wall, go up and over the front door and drop down from the ceiling. CU mounted high up next to ceiling behind front door. New CU is in the location of the original fuse unit, at Customer's request. But somewhere in that lot the tails go through a beam I reckon and are jamming up. Nothing I can't sort if I rip into the plaster ceiling she's just had done :( .

    In terms of load, I am sure a 60A fuse would be fine. 2BR mid terrace, newish combi for CH and HW. Biggest drain will be an induction hob she's got on order.

    There's no insulation anywhere near the tails that I can see looking from both ends. The tails will be less than 3m long.
     
  16. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Pop a 60A fuse in .............. nobody will ever know

    Tin hat still on!
     
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  17. Ian1981
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    Ian1981 Electrician's Arms

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    As long as regulation 434.5.2 is met for protection of the tails for fault current and your total load profile taking into account diversity is not going to overload the CCC of the tails you will be fine.
     
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  18. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    Of course the DNO may stipulate a maximum CSA of bigger than 16mm tails if connecting directly into their equipment.
    Of course we all ring them all the time to enquire don't we?:)
     
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  19. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
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    Wilko Electrics
    Yes, what was the DNO thinking putting 100A fuse in and saying nothing to owner (she's lived there forever) about the 16mm tails... and the DNOs smart meter guy ...
     
  20. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Got the books out, calculator valves just warming up.
     
  21. anthonybragg
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    anthonybragg Electrician's Arms

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    NORTHAMPTON
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    CHARLTEC ELECTRICAL LTD
    Take the tin hat off if you've got the fuse out de-rate the fuse to 60A there are millions of houses with 60A fuses that have had additional loads installed .
     
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  22. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Precisely.

    Got a client near me, 5 bed house, separate annex, loads of external lighting, pool, tennis court, ..... 60A fuse

    People get so hung up about needing a 100A fuse ................... unless you are doing space heating, cooking and water heating and live in a big house you won't get anywhere near 100A.

    Just imagine the lecky bill if you were running these loads on a regular basis.............
     
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  23. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
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    Wilko Electrics
    Ok - with k=115, S=16 and Ze 0.19 measured today, I get ... wait for it ...
    Mine included ... that's why I'm pretty comfortable with 60A fuse :) .
    Question is, do it myself (at least it's done) or ask DNO who may do it, or may not?
     
  24. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
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    hmmm. tails inside the CU are basically in free air, but with a slight derating due to be in the enclosure, although with plenty of airspace around. IMHO methed C can be applied without losing any sleep over it. if i doubt, replace the cut-out fuse with 80A. 16mm only gets lukewarm @ 110A. BS7671 figures are more pessimistic than me giving up beer.
     
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  25. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Edited that for you.............
     
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  26. Wilko
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    Wilko Electrician's Arms

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    Wilko Electrics
    Using 230 x 0.95, I get 1,150A pssc and plugging that into 434.5.2, I get 2.56 seconds. The melting time for BS88-3 100A at 1050A is 0.4sec.

    So for short circuit situation this 100A fuse will not damage the 16mm tails, if I've done that correctly :)
     
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  27. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    my old man's house, built 1926 has a 30A rewireable DNO fuse. it blew in 1988, but only when we;d added a 12kW cooker, 8kW shower,washing machine, and tumble dryer. all were going when the fuse let go.
     
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  28. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Just fit correctly sized conductors.
     
  29. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    I guess you must C2 every domestic installation that has 16mm tails and a 100 amp fuse arrangement without consideration other than 'it's not the right size'
     
  30. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    K would be 143 as the earthing conductor is not incorporated as part of a cable
    S= I2t square root /k
    So I is 1210 amps
    t I'd have to look up a bs 1361 or is it bs 88?
    K is 143

    Edit for some reason I'm working out the earthing conductor size so ignore me
     
    Last edited: Aug 16, 2017
  31. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    This wasn't the argument, the argument was the rating of said cable and my proposition that being partially contained should reduce the ccc. You have yet to give a flaw to this argument.
     
  32. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    You've yet to confirm yours.
    Show me evidence that cables need derating and to what method?
    Then I'll come around.
    Don't recall bs 7671 requiring us to derate cables entering a consumer unit or an enclosure in the appendicies with the list of reference methods it gives.
     
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    Last edited: Aug 16, 2017
  33. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Just ordered a couple of 60A fatboy fuses. Not saying where one might go :rolleyes:

    Edit : ok, just stop right there, you lot are just hopeless
     
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  34. Dave OCD
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    Dave OCD Electrician's Arms

    Location:
    Cornwall
    Business Name:
    Hendry Electrical Services
    They must be around a fiver a go now ?
     
  35. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Yes Dave, £3.83 from Discount Electrical.
     
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  36. wirepuller
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    wirepuller Trusted Advisor

    Location:
    south uk
    As has already been stated if there was a requirement to de-rate a cable entering an enclosure for termination clipped direct and free air installation methods would not be possible and would not be in the BYB.
     
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  37. Dave OCD
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    Dave OCD Electrician's Arms

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    That's not too bad mate, worth it for peace of mind and not being criticised to death by W10. :)

    Edit -reply to Wilko's post.
     
  38. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Clipped direct would apply between service heads and meters etc. Once contained at its termination to a CU alternative ccc applies. Really quite simple.
     
  39. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
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    Telectrix
    so what factor would apply to the cable rating just because it's inside a box? where in BS7671 does it say that a rating factor needs applying.
     
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  40. Karin
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    Karin Trainee Trainee Access

    Location:
    Kent
    just for the craic, tne or other cables are usually stripped back to single insulated conductors inside an enclosure (so may closer reflect singles in trunking for that part), meter tails are usually sheathed right to the termination point. would this (how much?) affect the argument?
    i've had a couple, there's no BYB in sight, i just wanted to get involved.. !
     
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  41. Ian1981
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    Ian1981 Electrician's Arms

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    Then there's no point in clipped direct is there? , as the worst case de rating factor must be used for the cable /circuit therefore clipped direct could not be used as a cables ultimate reference method
    Jesus!
    Got to be a wind up this?
    I'm done
     
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  42. Gavin John Hyde
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    Gavin John Hyde the lights are on but nobody is home

    Location:
    Kingswood
    Business Name:
    Sulis Electrical Services
    The seal fairies will appreciate your sacrifice and offerings of new fuses and continue to keep you safe in your work!:smirk::blush:
     
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  43. Dave OCD
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    Dave OCD Electrician's Arms

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    I doubt very much that he'll have much to say about this Ian. :)
     
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  44. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
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    I have already stated clipped direct can be used between heads and meters etc..
     
  45. Dave OCD
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    Dave OCD Electrician's Arms

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    Hendry Electrical Services
    You've got the wrong end of the stick Westward, check my post again, I wasn't referring to you.:rolleyes:
     
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