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Hot tub earthing question

Discussion in 'Electrical Engineering' started by Smog, May 20, 2005.

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  1. Smog

    Smog Guest

    Hi. UK question.
    I have a bit of a dilemma about a job that I was sent out on today.
    It was to install a feed for a new hot tub that a customer was getting at
    the end of the month. The concrete base was already down just outside the
    bedroom double patio doors and the tub was to be fitted about 2 meters away
    from the doors. The CCU was located at the front of the house on completely
    the opposite side, Grrr. We ran a 6mm T&E cable (4mm earth core) from the
    CCU (32A breaker (I think)), connecting it into the RCB side of the CCU,
    through the loft space and out and down the wall (in 25mm conduit) into a
    suitable isolator. About a 13 meter run from the CCU to the isolator, then
    another 4 meters to the hot tub. We then run 3 core 6mm SWA from the
    isolator, down the edge of the concrete, and eventually into the hot tub
    (when it's fitted). We also ran a 2.5mm T&E from the CCU (16A breaker),
    again connected to the RCD side in the CCU, out and down the same wall to
    feed a waterproof MK Masterseal double socket (NON RCD). The socket and
    the isolator where either side of the double patio doors from the bedroom.
    The customer mentioned, while we where there, that she was having a wooden
    enclosed structure built over and around the hot tub, once fitted, with a
    see through corrugated, plastic roof. She wanted the sockets, fitted within
    the enclosed area, less than 2 meters from the hot tub, for lights, Tv,
    radio etc etc
    My questions are:- are the sockets legal where they are situated and with
    this being a PME supply to the house, should the hot tub have an earth stake
    I heard a report today that one of the hot tubs we fitted, in a similar
    situation, by a colleague of mine under the same employer, had a problem in
    that when the customer stood outside the hot tub and touched the water
    within it, they had encountered a mild electric shock. I can only put this
    down to a potential difference building between the true earth (the ground
    outside the tub) and the water within the tub, PME earth. Could this
    possibly be down to the 13 meter run of the feed cable, the potential
    difference between the Neutral and Earth of the PME system and the 4mm size
    of the T&E Earth ?

    Any help on this subject will be greatly received, thanks.
  2. Smog

    Smog Guest

    That should read 'the RCD side of the CCU' and not RCB !
  3. John C

    John C Guest


    some thoughts.....

    I presume that the earth checks out ok when tested and is within the
    statutory limits for a combined neutral earth sytem.

    My own hot tub / outside socket network is similar but I have made small
    alterations. All outside wiring run thro' an MK split board with a 30mA rcd.
    I laid an earth mat around the area of the decking and bonded this to the
    main earth treminal incoming. I have no concrete slab. This was 70mm bare
    copper with earth rods every 6'. tested value was 1ohm. This suplements the
    CNE service.

    The housing of the hot tub had a seperate earth conection and I was able to
    connect this to the main earth also via a 6mm Cu conductor.

    there is no potential difference ( I just tried with a fluke )

    Hope this helps????

    John C
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