All I can add to this is that the wiring regulations state that the manufacturer's instructions must be followed. So, if the manufacturer states that a TT install is required for their kit, then a TT supply you shall have.

All I can add to this is that the wiring regulations state that the manufacturer's instructions must be followed. So, if the manufacturer states that a TT install is required for their kit, then a TT supply you shall have.

whjohnson said:

All I can add to this is that the wiring regulations state that the manufacturer's instructions must be followed. So, if the manufacturer states that a TT install is required for their kit, then a TT supply you shall have.

But if you do that, note 411.3.1.1 contains a requirement for all systems where ADS is used: Simultaneously accessible exposed-conductive-parts shall be connected to the same earthing system individually, in groups or collectively.

So, there IS a conflict here that ought to be addressed?

Therein lies the dilemma as the electrician is saying potentially two accessible conductive parts, hot tub (TT) and separate air source heat pump (PME), could be in contact so this is against regulations. The hot tub supplier and electrician are in contact and both agree they are right from their perspective. From the electrician's side he has risk assessed the hot tub and heat pump feed and his conclusion is that an individual could be in contact with conductive parts that would be on different earthing systems. The hot tub supplier view is that all hot tubs should be on TT to avoid PEN risk. Unfortunately they both accept each others position but cannot agree so I am left in the middle. My simple objective is that I want an installation that complies to the regs and puts me and my family at least risk (note did not say no risk all electrical systems pose some some risk)

The issue with 411.3.1.1 is it's in direct conflict with BS 7671, and part of the basic set-up for prevention of electric shock. So not complying with it is really not an option. The only way to comply would be to use barriers or insulation (if possible) to prevent "simultaneous contact".

John Ford said:

Unfortunately they both accept each others position but cannot agree so I am left in the middle.

If you can't "barrier or insulate" the exposed-conductive-parts of your products connected to PME earth, it would seem, unless you can make the whole electrical installation TT (which in some cases is not possible, but would certainly incur additional costs), there appears to be no way to install this particular product from this supplier, and comply with requirements of BS 7671 for safety, in your  particular premises. The only options available, if the supplier cannot change their view, are:

1. Different hot tub (or supplier); or

2. No hot tub.

We are not simply talking about whether to selectively comply with parts of a standard, but potentially whether an insurer may refuse to pay out, or whether someone (the electrician or hot tub supplier) may be prosecuted in the event someone gets hurt.

I doubt anyone on this Forum would advise you not comply with 411.3.3, and I doubt anything anyone on this Forum might say would cause the supplier to change their view?

Thanks for the information. As I understand more the main issue in the electricians mind is that there is a possibility that an appliance, strimmer / lawn mower for example, could be plugged into the outside socket 2.7 metres away from the hot tub and the person be in standing water on the patio next to the hot tub. I did some more dimensional checking and there is 240v wall light 1.3 metres above the top of the hot tub (supplier says regs say must be 2.5 metres vertically, assume this comes from zonal regs) that needs to be removed. There is another wall light  and 2.7 metres away. Hot tub supplier is happy with plug and light 2.7 metres away but not happy with 240v light 1.3 metres away. Air source heat pump is around 1.3 metres from hot tub. It would seem to me that the most likely risk would be someone touching the air source heat pump while being in contact with the hot tub. Would an acceptable solution be to TT earth the air source heat pump so the closest poetntial conductors woould both be on the same earth type.

John Ford said:

Would an acceptable solution be to TT earth the air source heat pump so the closest poetntial conductors woould both be on the same earth type.

It's not possible to answer without seeing the installation ... depends on whether the heat pump connects to other services (water, heating) or the electrical installation (including controls), connected to the PME earthing arrangement. Quite simply:

• If the heat pump is connected to metal pipework bonded to PME, then it's in effect part of the PME system (and then if you connect to hot tub TT, the hot tub is directly connected to PME earth, so no point in separating in the first place); or
• If controls etc, you might move the "TT being simultaneously accessible with PME" from outdoors to indoors.

Strimmers lawnmowers etc will not be earthed, and are not fixed installation. I think that concern can be discounted.  The PME earth stops at the socket. If someone chucks an extension reel in the pool then a TT supply or not is no longer the main concern.

As an aside to Graham's comments, in my own house I happily do not comply with BS7671, and am very content  to sign it off as safe. Bits of it are to an equivalent German standard, and that was good enough for both building control, and insurance who wanted  the building control completion cert.. , but he is right, I would not advise anyone else to do that ;-)  But it is dangerous to make assumptions about what others would recommend...

The fastest for the simultaneous access question is to make the ASP either inaccessible (some plastic or wooden fence or trellis perhaps ?)  or to move the tub by half a metre so the 1,5m becomes 2,0  !

M. 

gkenyon said:

We are not simply talking about whether to selectively comply with parts of a standard, but potentially whether an insurer may refuse to pay out, or whether someone (the electrician or hot tub supplier) may be prosecuted in the event someone gets hurt.

Or the householder gets sued. Most domestic insurances would probably cover this, but perhaps not if the householder knowingly had the installation erected without complying with BS 7671 (or any other standard).

Not that anybody would want to injure a guest in any event.

OK there seems to have been a perception that I am in some way trying to work around standards or complicit in a installation not in line with regs. Nothing could be further from the truth and that is why I originally posted, I wanted advice on the bet way to comply with current regs.  It appears that the electrician's position in signing of the feed as PME and the hot tub suppliers position in wanting TT are both compliant with the regulations. It should be noted that the supplier is an agent of a US manufacturer albeit the agent is on trade bodies and hot tub standards groups. The electrican phoned the NICEIC technical helpline in my presence and they responded robustly that there is no requirement for TT on hot tubs at present. Hot tub supplier says they regs will change soon to require TT on hot tubs and adds that without TT he takes no liability if something goes wrong and the water becomes live. The idea to move the heat pump or to make the heat pump inaccessible is a good practical suggestion and one that is easy to implement. In fact a single piece of trellis between the hot tub and the heat pump will make it impossible to be in contact with hot tub conductive parts and the heat pump.

All plastic piping from hot tub to heat pump, no connection between hot tub and house plumbing or outside tap. For TT I guess the heat pump would be wired the same as the hot tub rotary switch, the PME earth would end at the fused connection unit for the heat pump and the earth rod would be connected to the earth of the heat pump through the FCU. That said the suggestion in another post to make the heat pump inaccessible or 2 metres distant from the hot tub is easily implemented if I can get the hot tub supplier and electrician to resolve their different views on the earth type.

If the electrician is happy with that, then I guess there is no impediment to the two earthing systems Of course, not seen the actual installation in question.

I do worry about the proliferation of multiple earthing systems in relatively small-curtilage premises, but if this can be handled properly over the life of the installation, then I guess there's no issue.

All it takes, though, is for a future change where the installer (or maintainer) involved doesn't appreciate what was done earlier, and the apple-cart might be upset.