Hot tubs export TNCS or TT?

Discussion in 'Electricians' Talk' started by 14th edition, Nov 17, 2020.

  1. unphased

    unphased Screwfix Select

    Please expand on how a socket being used for the tub would introduce earth potential at the tub different to the supply earth.
     
  2. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    TN. . Sub main out from non-RCD side in SWA protected by 32A breaker

    TT As above but via RCBO

    Tub end. . .Small CU with RCD for TN. . .Main switch and breaker for TT to IP rated rotary isolator

    Sod rodding down, unless you have arms like Mr Tickle, difference in potential is not going to happen, all these electrocution chambers are nasty cihnk plastic anyway so no risk to anyone

    Make it visibly apparent its down to the consumer to test their residual current device, but none bother
     
  3. Bob Rathbone

    Bob Rathbone Screwfix Select

    We all recognise that the tub may be double insulated, the issue is not that a potential could be introduced at the tub, but rather into the area of the tub by any other class 1 appliance that may be plugged in at the same time and brought into the area adjacent or even close to the tub. The tub is to be fed by a socket outlet, probably a 2 gang outdoor type, anything that the user decides can be plugged into that spare socket, we have zero control over this, but we have a duty of care to be aware of it.
     
  4. unphased

    unphased Screwfix Select

    Sorry Bob I don't follow your explanation.
     
  5. 14th edition

    14th edition Well-Known Member

    Its not a plug and play and needs to be hard wired due to load, 3KW and two pumps , 1.5HP and I think 0.75 HP. For the life of me I can't see where or how you can put another consumer unit unless its indoors near the proposed hot tub. The tub suppliers can't even tell me whether its class 1 or 2 and I am simply not happy or confident enough to do this, particularly with such a wide range of views. I respect those views but have decided to bail out of this job, to iffy for me and I dont want to risk getting it wrong. Thanks for all the input!
     
  6. unphased

    unphased Screwfix Select

    I recently did a hot tub. I just put a two-way CU in the garage and fed it from tails directly from the meter box outside. 30mA 63A main switch, 32A mcb, 6mm2 3-core SWA, 40A rotary isolator wired as a dp, left 6mm2 tail for tub installers to connect. Its PME earth.
     
  7. Bob Rathbone

    Bob Rathbone Screwfix Select

    It appears that the tub is now fixed equipment and has no socket outlet for connection, assuming it is class 2 construction and assuming that the rotary switch for local control is in a non conducting case, exporting the earth, as it id not being used at the tub end, is not such an issue. But I still would not do it. This whole episode is a prime example of the Dunning Kruger effect in action, Google it, basically it explains that we must all know and recognise our limitations, but without that knowledge, how can we.
     
  8. sinewave

    sinewave Screwfix Select

    Darwins natural selection will apply to Hot Tub owners at some point!

    Carry on.............:D
     
  9. unphased

    unphased Screwfix Select

    How can an earth fault, around the tub, possibly find its way in to the tub or in to the electrcal connections? I don't know if any of those remarks are directed at me but nobody has yet explained why it is necessary to TT the tub? It appears to me that exporting PME is not understood. Get GN8 out.
     
  10. Bob Rathbone

    Bob Rathbone Screwfix Select

    Unphased, the 'remarks' or observations are general to this site and not directed at any individual. We all have our strengths and weaknesses, holes in our knowledge, call it what you like. I am retired and have the luxury of not having to make decisions driven by commercial need, this allows concentration on the facts alone and to be able to come to a conclusion not driven by customer need. Your question "How can an earth fault, around the tub, possibly find its way in to the tub or in to the electrical connections? " indicates that you may have overlooked the difference between true earth and the earth provided by the REC. It has nothing at all to do with any Live conductor (P or N) but with the CPC. The risk posed by an exported earth would be present even without the tub installed, just the supply being available, even if P&N were not connected, just the CPC (SWA). It is the presence of a CPC that may be at a non earth potential during a fault on the system, that is the issue in hand. I hope I have explained the issue effectively.
     
  11. a.refurb

    a.refurb New Member

    cheers
     
  12. Bazza-spark

    Bazza-spark Screwfix Select

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