4mm Ring, 2.5mm Spur?

Discussion in 'Electricians' Talk' started by Virtual Voodoo, Feb 19, 2007.

  1. Virtual Voodoo

    Virtual Voodoo New Member

    Gents.......

    32A 4mm T/E Ring main in an office, single socket spur required for a Water Cooler.


    Is it OK to spur off one of the existing double sockets in 2.5mm T/E?


    Cheers in advance.
  2. sparky Si-Fi

    sparky Si-Fi Well-Known Member

    Whats the water cooler rated at Voo..?

    4mm up to supply side of FCU then step down via 13A 1362 in the carrier in 2.5?1.5 for the Water Cooler mate.
  3. Virtual Voodoo

    Virtual Voodoo New Member

    Not fitting an FCU just a single socket outlet.

    Not sure what the coolers rated at, but assumed that as it's OK to spur in 2.5mm on a standard 32A 2.5mm Ring then why not a 4mm?

    Anyway I won't get 3 x 4mm conductors in a standard socket anyway so I guess it's got to be 2.5 anyway?
  4. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Not fitting an FCU just a single socket outlet.

    Not sure what the coolers rated at, but assumed that
    as it's OK to spur in 2.5mm on a standard 32A 2.5mm
    Ring then why not a 4mm?

    Anyway I won't get 3 x 4mm conductors in a standard
    socket anyway so I guess it's got to be 2.5 anyway?




    Even I don't see that as a reasonable design argument.

    Mr. HandyAndy - really
  5. sparky Si-Fi

    sparky Si-Fi Well-Known Member

    Not fitting an FCU just a single socket outlet.

    Got it soz!

    Not sure what the coolers rated at, but assumed that
    as it's OK to spur in 2.5mm on a standard 32A 2.5mm
    Ring then why not a 4mm?

    Yes Now I see your point yes mate no probs.(getting late and bureid in PIRs to complete)

    Anyway I won't get 3 x 4mm conductors in a standard
    socket anyway so I guess it's got to be 2.5 anyway?

    Yeah your right 4mm ring circuit could give you 50A + of rated current ! under best conditions so 32A breaker is well inside Current carrying capacity of that ring mate.
  6. Sherlock Ohms

    Sherlock Ohms New Member

    If it 4mm on a 32A MCB I bet it's a radial.
  7. X

    X New Member

    No problemo ... a spur from a 32a ring in 2.5mm is fine
  8. Virtual Voodoo

    Virtual Voodoo New Member

    If it 4mm on a 32A MCB I bet it's a radial.


    Me not stupid!


    It's a ring circuit alright, and quite common in bigger offices due to circuit length etc.


    Cheers everyone.
  9. SparkyJoey

    SparkyJoey New Member

    It is common not due to circuit length but more due to designers taking into account one leg of the ring becoming disconnected under fault conditions, therefore the 4mm being better equipped to handle the circuit load than 2.5mm
  10. spark&half

    spark&half New Member

    It is common not due to circuit length but more due
    to designers taking into account one leg of the ring
    becoming disconnected under fault conditions,
    therefore the 4mm being better equipped to handle the
    circuit load than 2.5mm

    I would say more due to the length still. not fault condition.
  11. SparkyJoey

    SparkyJoey New Member

    well that is one consideration, because I raised this question to an NICEIC inspector who took my 2381
  12. SparkyJoey

    SparkyJoey New Member

    also wot is the maximum floor area allowed to be covered by a 32A ring wired in 4mm T+E? I kno its 100m for 2.5. Is it greater for 4mm?
  13. sinewave

    sinewave Screwfix Select

    > It is common not due to circuit length but more due
    to designers taking into account one leg of the ring
    becoming disconnected under fault conditions,
    therefore the 4mm being better equipped to handle the
    circuit load than 2.5mm



    Sorry, Bollox that view!


    If we were to design circuits with the 'What if?' factor built in we'd be in a right mess with parallel 25mm SWA supplies all over the show! :O

    If anyone's gona fek about with their electrics it's gona be DIY Joe, not Professional Peter!

    ;)
  14. SparkyJoey

    SparkyJoey New Member

    yes I would Do it myself! However this was an opinion given to me by the NICEIC, so sorry it got ya back up dude! Anyways can u answer what floor area a 4mm ring can cover?
  15. sinewave

    sinewave Screwfix Select

    Me back aint up 'Dude', just sayin' like! ;)


    There isn't a tabulated floor area for 4mm T/E Rings cause it aint a 'Standard' circuit.


    You just have to design the owd fashioned way!
  16. Rob Roy

    Rob Roy New Member

    Agree completely with SparkeyJoey. Just spent a week-end in the hills with some sparkies and some electrical engineers. When they built their OWN houses, I wonder why they ALL used 4mm in their power rings.
    I repect the fact that others may have different views, but a few "what-ifs" are allowed in this world. That's why I took a shovel in the boot - in case it snowed.
    Did it - Yes! Did I need it - Yes!
  17. lightning bolt

    lightning bolt New Member

    yes its fine the 13 amp fuse will take care of the wire
  18. jumboscruit

    jumboscruit New Member

    Whilst it's normal practice to do a spur off a ring in 2.5 in domestic situations, I'm not so sure it's always OK in a commercial installation.

    Strictly speaking, you shouldn't drop down a cable size without fusing it, and any unfused spur should stay the same size as the circuit.

    Contrary to popular opinion, you can get three 4mm conductors into a standard socket outlet, you may have to keep all the strands straight though, to get them all in.
    I've done it lots of times.

    What you have to bear in mind, is not just will that 2.5 be enough for a water-cooler(Should be), but that circuit may be controlled by a type C MCB and PFC's in a commercial installation may be a lot higher than in a house. Mind you, the ecc in a 2.5 twin & e is the same size as in a 4mm tw & e.

    Not just that, but you have to allow for "functional earthing" now in a commercial installations, (high earth currents due to IT equipment), and the earthing should be run as a ring (high integrity earthing).

    JS
  19. jimmythemap

    jimmythemap New Member

    if there's a fuse at the load end protecting the 2.50 SQmm cable from overload then it's protected in the eyes of BS7671 albeit from the wromg end but still protected
  20. wklivesvtime

    wklivesvtime New Member

    christ there is alot of poo being spouted in this thread.
    With you sine all the way, lets wire everyting in micc.

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