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Hot tubs and PME

Hi, 

I am planning a hot tub install, and we circle back to the question of earthing arrangements! 
 

I am thinking of 3 different approaches to this as follows: 

 

  • PME to the isolator next to the tub, gland off and convert the output to TT creating an island.

 

Q: by doing this, how far away from the tub does the rod need to go? 

 

  • PME to the tub, and install a rod that is then supplementary to the PME.

 

Q: can this rod be next to the consumer unit or cut out, or does it need to go next to the tub? 

I understand the issue of touch/step voltages, but if a rod is installed next to the consumer unit and the tub is perhaps 10 metres away, would this be sufficient? 
 

  • PME to the tub, with a local rod as described in point 2 above, but with a Matt:e device that also protects for open PEN faults.

 

It isn’t possible to install an earth mat or grid, and the tub is likely going to be installed directly onto a concrete base, possibly with wooden decking surrounding the edges but not confirmed. 

I know this is a subject that is debated frequently but this is my first and I wanted to get some feedback. 

The TT solution would likely resolve many of the issues however the suppliers earth is better and isn’t dependent on weather and the soil! 
 

Thanks. 

 

Parents
  • vantech: 
    Thanks. 

    So here the ideal (well only) solution would be to TT the hot tub entirely? 
     

    How does this impact touch/step voltages? 

    To be honest, this is partly outside the scope of BS 7671.

    Some of the issues are to do with the supply conditions, the nature of extraneous-conductive-parts (and, if they are service cables or pipes, where they run).

    There is also the situation that BS 7671 requires that simultaneously accessible exposed-conductive-parts are connected to the same earthing system (Regulation 411.3.1.1) - so yo must be very careful if there are two earthing systems in the same installation.

    So, it's all down to the designer's assessment.

Reply
  • vantech: 
    Thanks. 

    So here the ideal (well only) solution would be to TT the hot tub entirely? 
     

    How does this impact touch/step voltages? 

    To be honest, this is partly outside the scope of BS 7671.

    Some of the issues are to do with the supply conditions, the nature of extraneous-conductive-parts (and, if they are service cables or pipes, where they run).

    There is also the situation that BS 7671 requires that simultaneously accessible exposed-conductive-parts are connected to the same earthing system (Regulation 411.3.1.1) - so yo must be very careful if there are two earthing systems in the same installation.

    So, it's all down to the designer's assessment.

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