UK 32a supply for a hot tub of a PME supply.

[Scottishlad123]

Hi there,

I have been asked to install a 32a supply for a hot tub for a client. I haven’t installed a supply for a hot tub before and having done a bit of research I am getting mixed answers about doing this on a PME system. I have a DB under the stairs with plenty of spare ways so I would be planning to take a 6mm armour from here outside to a rotary isolator. what I am unsure about is the earthing scenario, I have seen a lot of people saying this will require an earth rod. There is also the possibility of taking tails directly of the Henley blocks into a small garage unit and feeding the hot tub of its own DB. Any help is greatly appreciated thanks in advance.

 

[Mark.fardon]

Great thanks for that. So purely for the potential danger under lost PEN. In the case of an older house/neighbourhood then it’s likely that gas and water services will be metal and many will be bonded to their respective ETs so I suspect under the DNO fault scenario these would pull the extraneous voltages down very low especially as would be acting in parallel ? I guess all the above applies to EV charging issue also

 

[pc1966]

Great thanks for that. So purely for the potential danger under lost PEN. In the case of an older house/neighbourhood then it’s likely that gas and water services will be metal and many will be bonded to their respective ETs so I suspect under the DNO fault scenario these would pull the extraneous voltages down very low especially as would be acting in parallel ?

Certainly many houses will be bonded with low impedance together in older setups with metal pipes for gas & water, there you might see sub-1 ohm Ra but equally you would have many parallel bonding paths to the shared service pipes (assuming properly wired homes).

But it can't be depended upon and most gas and water mains these days are plastic, so over time that route for voltage equalisation will go as leaky/corroded mains pipes are replaced.

 

[davesparks]

ps I'm still unsure the logic/reason for seperating the PME earth from a "TT"'d installation for eaxample to an outbuilding when you could equipotentially bond it back or via a marshalling terminal to the PME earth ? (providing you have the correct size bonding conductor)

Don't forget that regulations cover all installations, not just little domestic ones.

The point is that sometimes running a main bond back to the MET is not possible.
For example you are installing a supply to a portakabin type classroom at a school which requires main bonding to an extraneous part.
There's a suitable DB to supply it from around 20 mtrs away and you calculate that you need a 10mm 4 core SWA, however the size of the incoming supply dictates that the main bonding needs to be 50mm and the DB you are coming from doesn't have a 50mm connection back to the MET.

So you are faced with a choice of running a 50mm bond 120m long back to the MET, or setting up a seperate TT system for the portakabin.

Hopefully it is obvious that it's simply not economically viable to run that main bond, it woukd probably quadruple the price of the job.

These are the kind of situations where setting up a seperate TT system is the only realistic option.

Scaling it back to domestic installations where main bonds are usually 10mm it is often possible to run that main bond, but people choose not to for various reasons. Sadly the reason is often a lack of knowledge or understanding.

 

[Mark.fardon]

Great post really good point

 

[Midwest]

I’ve been reading threads like this with some personal interest. I’m thinking of buying one of those inflatable hot tubs, primarily as a glorified paddling pool for my grandson.

I was quite happy to plug into my outdoor socket on my decking (pme supply), but I keep reading these sorts of threads Another Hot Tub Thread which makes me re think.

A 10mm supply cable might be difficult to get to the back of my place, but I might be able to get an earth rod in at the front.

The manufacture recommends ‘connecting the spa pump to an equipotential bonding terminal with a solid 2.5mm copper conductor’.

Your thoughts, or am I over thinking this?