AJJewsbury said:

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).

I do see that - I'm thinking in my head about the fact that if we have low-impedance connection with Earth from extraneous-conductive-parts, plus low impedance connections (10 sq mm or greater, short-distance main protective bonding), this presents overall lower resistance path to Earth than  a longer run of larger cpc + connection to Earth of exposed-conductive-parts (with cpc's already connected back to MET).

plus low impedance connections (10 sq mm or greater, short-distance main protective bonding),

Which is fine if the bond is there. The trouble for me is that BS 7671 seems to be saying it's no longer required (as the part is outside of a building).

   - Andy.

But BS 7671 has been updated to recommend that a supplementary earth electrode is provided for TN systems (Reg 411.4.2) so there ought to always be at least something connected to MET acting in this capacity - we have already agreed how the protective conductor connecting the electrode to MET ought to be sized ?

hello GK hello AJ   Thanks for hanging in there . Not sure I understand all the dialogue 

Im rather stuck here :  Take on board  belt and braces 10mm2 for the earth link met to rod. That done.

Can I hope for some kind of indication the earth proposal is in fact SAFE   Given all other parts equal and installed by qualified.

Answer to that is stopping everything.  

I still have a number of questions about the solar package   Is there a solar forum on this net ?

Solar installers seem to just have menus.. Certainly cant negotiate this.

ciao MsO  

But BS 7671 has been updated to recommend that a supplementary earth electrode is provided for TN systems

We might be at cross purposes here... a supplementary electrode - with no particular requirement for resistance - so let's say 200Ω - vs either a km long perimeter fence with steel uprights in the ground every 2.5m - let's say <1Ω overall to the general mass of the Earth- or a outside light on wrought iron railings that are continuous to next door's similar light which is similarly connected to their MET by a thin c.p.c. - say 1Ω or 2Ω to the supply PE - seems to me the bulk of the current is going to prefer the little c.p.c.s ....

   - Andy.

Can I hope for some kind of indication the earth proposal is in fact SAFE 

It certainly look sensible in principle to me. At this distance I can't guarantee it's SAFE (there could be all sort of minor looking details that could get in the way that I can't see - such as arrangements for ADS) but I can see nothing in the earthing arrangements per se to object to so far.

... on second look at the diagram I notice it seems to be proposed to locate the battery storage system in the loft .... there have been some very recent discussions about that .. and a new standard published (PAS 63100 I think) which might have potentially moved the goal posts a bit on that score. (Who said cutting edge technology wasn't exciting (or even infuriating)?)

  - Andy.

It's amazing how complicated a bunch of electricians can make a bit of bonding (I'm not actually an electrician, but a member of the IET).

Outside the IET, you migh want to look at the "Green and Ethical Moneysaving" section of the Money Saving Expert forums.  https://forums.moneysavingexpert.com/categories/green-ethical-moneysaving,  You won't get expert electrical advice, but you may get information from solar experts.

thankyou AJ OK then I have confidence to proceed >  Be assured I am not holding anyone here for a verdict   Will leave that to my electrician sign off  when I finally contact : 

So many obstacles : Yes Volatile  lithium batteries Batteries in the house has been a concern would prefer in garage alas at end of garden . some 20m.  Apparently there is a no  to sending 200V dc or so underground  No shock protection against DC?  

Contacted my home insurance company : Disnt care about fire risk : I made sure they understood issue was about batteries in house not roof solar panels 

Is there a practical solution :  Do please let me know  Solar suppliers seem just menus take it or leave it . In the Loft.

ciao Ms O 

So many obstacles : Yes Volatile  lithium batteries Batteries in the house has been a concern would prefer in garage alas at end of garden . some 20m.  Apparently there is a no  to sending 200V dc or so underground  No shock protection against DC?

Indeed - hence the more usual design solution of using a.c. between the house and garage in that situation (PV inverter in the house to convert d.c. from the panels to AC then the battery system converts a.c. to d.c. to charge the batteries and inverts back again to a.c. when supplying loads). With a conventional grid-tied solution is comes out in the wash.

In the Loft.

Unusually for BSI, PAS 63100 is available as a free download so you can see for yourself - https://knowledge.bsigroup.com/products/electrical-installations-protection-against-fire-of-battery-energy-storage-systems-for-use-in-dwellings-specification?version=standard

  - Andy.

Hello Andy  "conventional grid-tied solution it comes out in the wash." I know you guys dont get this but as a punter if you contact solar suppliers . The glossies just look like greenwash to me.  

Love some simple answers ...  

 To begin  to size: no of panels / and number of sunlight hours I need in my area to boil  my ketlle ?  To run my washing machine for one hour . ?  ( No battery) thats the starting point. 

Can I switch a battery bank in and out  ( myself) according to time of year ? 

etc  ciao  Ms O