Plug & Play Hot Tubs.

I have only seen two plug and play hot tubs. One had a 10mA RCD in the power cable. Apart from pressing the test button there were no accessible connections to test it properly.

I have not seen the wiring on the second, apart from the extension cable out of an adjacent window, but it is mounted on wooden decking so the risk would appear to be low. 

But as there do not appear to any reports of people receiving shocks from them are we worrying unduly about the risks. Especially when compared with the number of people dying from falls on stairs. ( over two per day)

kfh: 
 

I have only seen two plug and play hot tubs. One had a 10mA RCD in the power cable. Apart from pressing the test button there were no accessible connections to test it properly.

I have not seen the wiring on the second, apart from the extension cable out of an adjacent window, but it is mounted on wooden decking so the risk would appear to be low. 

But as there do not appear to any reports of people receiving shocks from them are we worrying unduly about the risks. Especially when compared with the number of people dying from falls on stairs. ( over two per day)

 

It is probably not a good idea to locate a hot tub at the top of stairs. Some users have been known to imbibe whilst using a hot tub. And don't adverts always seem to show wine glasses located on the sides of hot tubs?

It is that we thinking sparks do implement safe installations that low numbers of people suffer electrocution when using hot tubs. Still, P.M.E. earthed hot tubs may produce slight shocks due to step Voltages,  and that is not good. Water at above zero potential, earth at real Earth potential. In this case no legs good, two legs bad. Apologies to the bloke wot rote Animal Farm.

Z.

If the manufacturers (the ones who will likely get the blame / bad-publicity if people start getting tingles or shocks from a hot tub) are happy for it to be connected to a PME system by end-users, might we suspect that either there aren't any exposed-conductive-parts or they're so far behind plastic pipework that even given the resistance of the water the chances of a noticable shock must be minimal. 

   - Andy.

The N.I.C.E.I.C's view point.

“Hot Tubs and TN-C-S Supplies The NICEIC Technical Helpline is often asked whether a hot tub installed outdoors may be supplied from a circuit taken from an installation forming part of a TN-C-S system, often referred to as a PME Supply. Neither the Electricity Safety, Quality and Continuity Regulations nor the guidance given in Engineering Recommendation G12/4 – Requirements for the Application of Protective Multiple Earthing to Low Voltage Networks published by the Energy Networks Association places any restrictions in respect of the connection of a hot tub to a PME supply. G12/4 does offer several alternatives in respect of the connection of a swimming pool to a PME supply and it is sometimes suggested, erroneously, that hot tubs should be treated in the same manner as a swimming pool. However, it is clear that hot tubs fall outside of the scope of Section 702 of BS 7671 (see Regulation 702.11). So, unless, as stated previously in this article, a hot tub outdoors is installed within the zones of a swimming pool, only the general rules of that standard are applicable.”

Z.

AJJewsbury: 
 

If the manufacturers (the ones who will likely get the blame / bad-publicity if people start getting tingles or shocks from a hot tub) are happy for it to be connected to a PME system by end-users, might we suspect that either there aren't any exposed-conductive-parts or they're so far behind plastic pipework that even given the resistance of the water the chances of a noticable shock must be minimal. 

   - Andy.

The polluted water with many additions may be quite conductive. It will no doubt run past earthed metal sheathed water heating elements(s) where it could become live. The water will be electrically connected to the P.M.E. earth system in a T.N.C.S./P.M.E. supplied circuit. Certainly a risk outdoors.

I suggest a greater potential shock risk than P.M.E. supplied caravans, boats or catering units.

Z.

The polluted water with many additions may be quite conductive.

But how conductive? In the early experiments with plastic pipes it was noticed that central heating inhibitor produced a very noticeable reduction in water resistance - yet even with a double dose of inhibitor a few tens of cm of plastic pipe was still quite sufficient to keep any possible shock currents well below danger levels. Unless we're expecting the ‘pollution’ to consist of magnetised iron filings, how conductive is the water really likely to be?

   - Andy.

I have see those inline 10mA RCD with a 13A plug for a Japanese toilet seat. The whole thing was sealed with not enough cable between the RCD and plug. Clearly they had not thought about 3m rule for sockets in a room contrain a bath or shower. 

Partly the UK is pretty much unique in its 3m rule(*) - most 230v countries only exclude sockets in zone 1 and any places where splashing is expected. Ypu may think that if the loo really is that close the bath or shower and there is no screen in the way, then it's probably not in a great place anyway. We do seem very keen to ram showers and loos into very small spaces, especially in flats. It may be that not all of these are really suited to mains wired loo seats etc.

Mike.

(*) I did note in the previous draft for comment of BS7671, the 3m had magically become 2m, and that may help a few borderline cases.  but if that really passes into the final version of the 19th edition or whatever, we shall have to wait and see.

AJJewsbury: 
 

The polluted water with many additions may be quite conductive.

But how conductive? In the early experiments with plastic pipes it was noticed that central heating inhibitor produced a very noticeable reduction in water resistance - yet even with a double dose of inhibitor a few tens of cm of plastic pipe was still quite sufficient to keep any possible shock currents well below danger levels. Unless we're expecting the ‘pollution’ to consist of magnetised iron filings, how conductive is the water really likely to be?

   - Andy.

Salt.

I do not think that central heating inhibitor is used in hot tub water.

What are the risks to persons using a hot tub?

The risk of electric shock is increased when a person is wet due to the decreased body resistance which allows an increase in current through the body in the event of contact with live parts. This risk is further increased when a person is using a hot tub outdoors due to the possibility of contact with Earth. Which is exactly the same risk as for a person using a swimming pool.