Hot tub installation

The concern folk have is the possibility of an offset voltage between the terra-firma earth (wet feet) and the PME earth (the suppliers) . This is similar to the car charger problem, with the additional complexity of a wet and lightly clad victim,  and as per the previous reply, the ideal solution is the same, a TT island well away from the rest of the electrical system. 

How serious this really is depends on a number of things, not least if the user can credibly make good contact to both at once.  There will be situations, arguably most,  (hot tub on raised decking or other insulating surface come to mind) where the PME earth would be fine - and remember there are loads of PME earthed lamp-posts, bus stops etc that folk touch with impunity, as shoes and paint conspire to ensure any contact is not a dangerously low resistance.

A badly done TT where the zones are not properly separated or the ADS is not right, (pre RCD live in a metal container relying on the TT earth for example) is probably worse than using the  PME, if it actually increases the risk of shock in fault or of somebody bridging two earthing zones by bringing them close  TT earthing of a metal box on the wall beside some outside light or other thing supplied by the PME earth for example.

I suspect that a great many domestic hot tubs do in fact use the house earth, without incident.

Mike.

PS I also disagree with the advice in the PE article above that implies an earth rod of 20ohms or so in parallel the suppliers earth  is going to have any significant effect on all but the weediest of PME supplies in the event of a lost PEN.

More likely the rod, and a carrot shape of earth around it gets pulled up to the fault voltage increasing the step-voltage shock risk if the top of the rod is accessible.

The concern folk have is the possibility of an offset voltage between the terra-firma earth (wet feet) and the PME earth (the suppliers) . This is similar to the car charger problem, with the additional complexity of a wet and lightly clad victim,  and as per the previous reply, the ideal solution is the same, a TT island well away from the rest of the electrical system. 

How serious this really is depends on a number of things, not least if the user can credibly make good contact to both at once.  There will be situations, arguably most,  (hot tub on raised decking or other insulating surface come to mind) where the PME earth would be fine - and remember there are loads of PME earthed lamp-posts, bus stops etc that folk touch with impunity, as shoes and paint conspire to ensure any contact is not a dangerously low resistance.

A badly done TT where the zones are not properly separated or the ADS is not right, (pre RCD live in a metal container relying on the TT earth for example) is probably worse than using the  PME, if it actually increases the risk of shock in fault or of somebody bridging two earthing zones by bringing them close  TT earthing of a metal box on the wall beside some outside light or other thing supplied by the PME earth for example.

I suspect that a great many domestic hot tubs do in fact use the house earth, without incident.

Mike.

PS I also disagree with the advice in the PE article above that implies an earth rod of 20ohms or so in parallel the suppliers earth  is going to have any significant effect on all but the weediest of PME supplies in the event of a lost PEN.

More likely the rod, and a carrot shape of earth around it gets pulled up to the fault voltage increasing the step-voltage shock risk if the top of the rod is accessible.