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.

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.

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.

Thanks very much for your help and for all the comments, they have helped me get to a solution to propose to the hot tub supplier and electrician. Seems like TT earth for hot tub is sensible and meets suppliers requirement and to satisfy regs make sure all fixed sockets, wall lights are at least 2 metres away or moved/removed. Final piece of jigsaw would be to have a physical barrier between hot tub and heat pump to meet the requirements of 411 3.1.1z