Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 36 replies
  • Subscribers 32 subscribers
  • Views 3020 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

HOT TUBS ANY VIEWS OR ISSUES?

John Peckham
I have been chatting to a mate of mine who is a very experienced sparks who does 10-15 hot tub installs a year. He TTs his supplies to hot tubs which are on PME supplies which is the majority of supplies in Essex other than the odd TT supply in country areas.


He does get called back to hot tubs that he has not carried out electrical installations because people climbing in and out of the hot tub where people have experienced "tingles" ie minor electric shocks. Sure enough these shocks are due to the hot tub being directly connected to the PME earth.


Currently (excuse the pun) BS 7671 701 and 702 do not cover hot tubs only the general rules in Parts 1-6.


Does anyone on the forum carry out hot tub installations and if so how do you do it? Has anyone been called to investigate "tingles"? Does anyone know of any more serious shocks or injuries relating to hot tubs or any other equipment connected to a a PME supply?


Thanks in anticipation.


JP


  • 0
    John Peckham:


    Has anyone been called to investigate "tingles"? Does anyone know of any more serious shocks or injuries relating to hot tubs or any other equipment connected to a a PME supply?



     




    Going back to the original post, the question was about “tingles”under normal operating conditions rather than life threatening “jolts” under fault conditions.


    So we need to prevent the tingles whilst being able to clear the faults, that seems to lead most of us to us TT earthing and to rely on a 30 mA RCD.


  • 0

    Which sort of leads me in a rambling manner to just how effective is a plastic insert in a metal water pipe?


    The complexity with with  water is that the conductivity is a strong function of what is dissolved in it.

    Pure, really pure, distilled and then de-ionised water at room temperature is many megohms-cm. That is to say if made a cubic cm tank and metallised two opposing surfaces and made the rest of perfect insulator,  the resistance would be perhaps 10 megohms.

    But dip your slightly sweaty  finger in it, even for a second, and the resistance falls to  a few hundred k.

    Add a small pinch of salt and you  get change out of a hundred ohms.

    Water on the ground , even rain water, has enough dissolved solids to be a respectable conductor at the level of low tens to hundred kohm-cm depending on the air pollution level of the day.


    Actually the simple water purity/ hardness meters that report 'dissolved solids %' or "TDS" are really just a controlled resistance measurement scaled by some assumption that relates resistance to concentration of some test solutions. (look up table here)


    Tap water, in the UK at least, meets or exceeds a minimum purity standard  link - the levels are in Schedule 1 to the act that indirectly sets a limit to conductivity equivalent to the worst case level of contamination, of about 0.2 grams of salt per litre perhaps  TDS a of a few hundred Parts Per Million,  and a resistivity over that test cubic cm of a few thousand ohms.

    In practice a 10cm length of cm of  15mm dia plastic pipe will add at least some ten  K ohms, to mains water and in most parts of the country rather more.


    That is not however  going to work for water in  closed loop heating system that is not drinking quality, nor for recirculating  ponds or fish tanks, nor I suspect water in hot tubs or paddling pools once someone is in it.

    M.


    (Note that sea water is 30-40 grams per litre so perhaps 150 to 200 times more conductive - I'd expect the hot tub not to be that bad.

    (Unless some one adds Tingly bath salts,)   " A special mix of Epsom salts, eucalyptus, peppermint, spearmint, Spices, Chicory root, roselip and liquorice perfect for a minty tingly bath. All ingredients and tools are cleansed and charged before creation " !!

  • 0
    Zoom


    I meant this one. https://issuu.com/hamervillemediagroup/docs/iet_virtual_showcase?fr=sOGExYjM1MTc1OTA


    Andy. Thanks for the You Tube link which is worth a view as it demonstrates the hazard around safe isolation of PME supplies.
  • 0
    I once measured the resistance between two radiators connected by a pair of approx 3m plastic pipes - it was 300 KOhm
  • 0
    wallywombat:

    I once measured the resistance between two radiators connected by a pair of approx 3m plastic pipes - it was 300 KOhm


    May be that was due to the Fernox in the pipes.


    I think that we can all agree that water in pipes is not a complete insulator (does such a thing exist?), but I'd settle for 23,000 Ω.


  • 0
    John Peckham:

    Zoom


    I meant this one. https://issuu.com/hamervillemediagroup/docs/iet_virtual_showcase?fr=sOGExYjM1MTc1OTA


    Andy. Thanks for the You Tube link which is worth a view as it demonstrates the hazard around safe isolation of PME supplies.


    Hello John. Yes thanks I did view that video about P.M.E. I found it very useful and most interesting.


    Z.


Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines