What sort of approval / sign off are you looking for?

Any electrician can install a couple of bits of green & yellow stripey wire, and an earth rod if you don't already have one.  You could even buy the bits and do it yourself if you know what you're doing.

Anne Otis said:

Arrangement is similar to UPS systems 

Not really, a UPS would typically have a "bypass" to grid mains, and conform to specific standards that also relate to the specification for reliability, power quality, backup means and backup time.

Anne Otis said:

I cant find one ?? Can anyone put me in touch with such a person locally ?  Or is there a directory ?  I am in south london close to Morden Northern Line tube

Have you tried the following:

• https://search.napit.org.uk/
• https://niceic.com/find-a-tradesperson/?gad_source=1&gclid=Cj0KCQjwudexBhDKARIsAI-GWYV7WjCE7bK-x3hwD2ZWZHGeSE0ZzOmE0a63JIwcSHn-VTgNT9sMMfQaApG0EALw_wcB

See attached schematic 

Pedantically, the rod will effectively be an extraneous-conductive-part as far as the grid supply is concerned - to which it's almost certain PME conditions will apply - thus 6mm² will be too small - the minimum will be 10mm² (possibly more under some conditions). Physically the soil resistance around the rod will limit the current the bonding conductor can carry, so the 6mm²  will be perfectly adequate in practice, but BS 7671 (and associated PME requirement) don't recognise such subtlety, so if you want someone to certify it as complying with BS 7671 and/or building regs, that might have to increase a bit.

final approval / sign off 

Note that BS 7671 certification isn't a final exam kind of thing - more like continuous assessment - as the designer and installer have to sign as well as the inspector/tester. Some may be happy to 'oversee' you doing some of the work, but typically will need to be involved at each stage to do that.

   - Andy.

AJJewsbury said:

Pedantically, the rod will effectively be an extraneous-conductive-part as far as the grid supply is concerned

I disagree. Perhaps, even more pedantically, it can't be an extraneous-conductive-part by definition, as it's part of the electrical installation. From Part 2:

Extraneous-conductive-part. A conductive part liable to introduce a potential, generally Earth potential, and not forming part of the electrical installation.

It's relationship to the TN grid supply is effectively a supplementary earth electrode as discussed in Regulation 411.4.2.

AJJewsbury said:

PME conditions will apply - thus 6mm² will be too small - the minimum will be 10mm² (possibly more under some conditions).

I do, however, fully agree with your view on sizing the conductor connecting it to the installation ... it will see the same currents as an extraneous-conductive-part even though it's not one, and therefore where PME conditions apply, the minimum cross-sectional area ought to be according to Table 54.8 of BS 7671 in relation to the grid supply

I disagree. Perhaps, even more pedantically, it can't be an extraneous-conductive-part by definition, as it's part of the electrical installation.

Fair point. Another example of where the definition doesn't exactly help with what the physics tells us we need to achieve. (Similarly with c.p.c.s to class 1 equipment outdoors that's in contact (directly or indirectly) with the general mass of the Earth).

   - Andy.

AJJewsbury said:

(Similarly with c.p.c.s to class 1 equipment outdoors that's in contact (directly or indirectly) with the general mass of the Earth).

I'm not with you 100 % on that ... surely the issue with the physics here is making sure the diverted neutral current goes where you want it to, because larger currents will take the path of least resistance (hopefully extraneous-conductive-parts), and therefore helping keep touch-voltages that might result at the outdoor equipment to a minimum by providing some local earthing within the installation via extraneous-conductive-parts? We'd definitely prefer the current to exit via good earthing offered by real extraneous-conductive-parts, than a cpc to an item of Class I equipment.

There is a gap, though ... what if there are no extraneous-conductive-parts in the installation (plastic water pipes, no gas, no metal structural parts in contact with the ground?

The recommended supplementary earth electrode in Regulation 411.4.2 would help to address that gap, but only if the protective conductor connecting it were sized in the same way as a main protective bonding conductor. (Although I don't want to give the impression here that the electrode is recommended solely for the reason of back-filling for the job that water and gas pipes, and PILC or hessian covered distribution cables, once did - as prosumer's electrical installations become more common, a supplementary earth electrode will become a necessity.

Maybe simon , even some suggested that since it is not connected to grid just do it and ignore regs ( like in Devon lol)  

But no I am not qualified to todays standards

 I seek assurance that what is proposed  is in fact safe If in doubt I wont do it

The assurance of sign off by registered qualified

My local guy just "dont know"  None of his colleagues either 

Might add This solution is clear of all the greenwash around.  If its a sunny day put your washing on the line Plug our kettle in.

Ciao Ms O

thankyou I will try that : Fascinated by the arguments  though too fat our of date to appreciate them. 

To reiterate  I have no intention of installing this myself  I want assurance the proposal is in fact safe. Cannot start without that  If there is is doubt I wont do it . Do think the concept has merit. If possible 

The solution was proposed previously on here but I need to be sure. Is there any mileage in comparing  to new EV charging rules that have NO earth rod 

( Diagrams of current flow under fault would be instructive to my learning but hey .  Thank you again.  

I'm not with you 100 % on that ... surely the issue with the physics here is making sure the diverted neutral current goes where you want it to, because larger currents will take the path of least resistance (hopefully extraneous-conductive-parts),

I'm thinking of of class 1 items (say a luminaire) attached to some very substantial metalwork outdoors (say steel perimeter fence, or a bridge) or even something that has a connection with another installation's earthing system (the "Downing St" issue - where outside lights are mounted on a wrought iron fence that's common to adjacent buildings). BS 7671 no longer requires main bonding to extraneous-conductive-parts outdoors, so we're potentially left with a simple c.p.c. trying to handle the currents (diverted PEN or otherwise) that normally would be shunted by a main bonding conductor).

  - Andy.