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CONSUMERS TAILS IN THE OSG

John Peckham
I have just been having a scan read of the latest edition of the OSG. On page 20 it says in respect of consumers tails, " Polarity should be indicated by the colour of the insulation and the minimum cable size should be 25mm".


Alongside this statement is a reference to 514.3.1. I am OK with the requirement in 514.3.1 for the colour of the insulation but where  does the requirement come from for the CSA to be 25mm?


I do know some DNOs representatives may require a minimum CSA of 25mm but I suspect that this is a personal preference. My thinking is this is one of the myths and legends of electrical installation work that has been repeated so often that it has become fact. My view is the tails need to be sized to take the maximum load and they also need to be co-coordinated with the supply fuse. In addition some older consumer unit terminals will not take a 25mm tail.


Can anyone direct me to a reference source that requires the minimum CSA of meter tails to be 25mm?


  • 0
    Doing some back of a fag packet sums I reckon that a metre length of 16.0mm2 copper meter tail carrying 100 Amps will create about 12 Watts per meter of heat. O.k. in free air I suppose. Ignoring Volt drop on this occasion.


    Z.
  • 0
    per metre of meter tail.


    ?


  • 0
    To err is human, to forgive divine.


    Z.
  • 0
    This is probably more dangerous that undersized meter tails.......

    https://www.youtube.com/watch?v=ij3jDdGKbfg


    Z.
  • 0
    As the ancient bard sayeth, "Meter tails, meter tails how comely though art."

    https://www.youtube.com/watch?v=edO3qb0RtiU



    Z.
  • 0
    It is not an ideal world. For a 100amp main switch we would expect  cable sizes of 25mm2. However, if the main fuse is 60amp and the meter is less than 100amp 16mm2 is acceptable.  A 60 amp main switch could also have 25mm2 tails, but 16mm2 are more common. Most meter guys these days changing a meter and finding existing 16mm2 consumers tails will fit Henly blocks and tail into the meter with 25mm2. We must also remember some cut-outs wont take 25mm2 so cut out to meter is 16mm2.at the end of the day it all comes down size of fuse at the origin. As regards G Kenyons query, we wont change 60 to 100 cut outs on demand because the supply may be limited. 


    Regards, UKPN
  • 0
    I have witnessed , on a few occasions, the supplier putting in 16mm tails if a 80A cutout fuse or less and being happy to connect it to my 25mm . They even change the cutout from 100A to 80A to accommodate their sixteen tail syndrome 'cos "it's all we carry"
  • 0
    Three weeks ago I took sole responsibility for connecting the tails of the new installation that I had installed into the new suppliers meter, neither metering services or the DNO would have done it for me or taken responsibility if there had been a big flash and a bang.


    Had I chosen to install 16 mm tails rather than 25 mm tails, as far as I know no one would have stopped me from connecting them.


    Sometimes I think I’m in a parallel universe that looks the same, but where the rules of life are different.  


    Andy B.
  • 0

    Sparkingchip:

    Three weeks ago I took sole responsibility for connecting the tails of the new installation that I had installed into the new suppliers meter, neither metering services or the DNO would have done it for me or taken responsibility if there had been a big flash and a bang.


    Had I chosen to install 16 mm tails rather than 25 mm tails, as far as I know no one would have stopped me from connecting them.


    Sometimes I think I’m in a parallel universe that looks the same, but where the rules of life are different.  


    Andy B.




    Probably a parallel universe created by Douglas Adams?


    Z.

  • 0
    A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.


    Douglas Adams

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