Thanks, I've actually found what I think must have been the earth source (See new picture below) .... but it's been cut off? I'll replace this with a new earth (Earth rod or maybe use the metal water piping as I know we have a long run "of over 200' uninterrupted" and no nearby neighbours to cause feedback issues?)
All "extraneous conductive parts" should be bonded to your earth anyway, this means metallic service pipes or steelworks that are in contact with the true Earth. This applies to
any supply system as you want to avoid finding an appliance with metalwork on one CPC system being at a different voltage to something else you can touch on another.
In the UK at least you are not allowed to
rely on a water pipe as a means of earthing, basically because it can be changed at any time by a plumber or the water supply company and it will likely be replaced by plastic (or plastic joint) so it may become un usable and by folks who know little of, and have no requirement to, deal with electrical aspects.
So while you might have a fantastic earth due to a long length of private metal pipe, you probably should add a dedicated rod and that would be the basis for
designing your system if
TT. Basically on a TT system you measure the rod Ra, if that is low enough to be stable (UK regs below 200 ohms) that can then be used to select means of fault disconnection. almost always a RCD (or RBCO) as you are very, VERY unlikely to have a rod able to trip a 32A MCB or whatever.
So it looks like I have a TT supply but with TN-C internal wiring?
No, if the CPC is linked to the supply neutral by a wire it is TN.
If those wires are separate at source it is TN-S, if there is only one wire (N & CPC) then it is TN-C
It is only if your CPC system is
only linked to the supply
through the Earth itself by means of a rod, buried foundations, etc, that you have a TT system.
I've bought a typical UK type populated CU over from the UK, which I'll fit in the next few days. But; I'll split it to connect the TNC wiring on one side through MCB's with co-joined earth / neutrals, and on the other TT + Earth (still co-joined to incoming N) but with RCD protection as I slowly swap over the wiring from two core (L + NE) to three core (L+N+E).
Does that sound a sensible plan?
I'm not sure I quite understand what you are proposing. More worryingly, I'm not sure you understand it either!
Trying to have a mixed earthing system seems to me to be a recipe for disaster if something goes wrong on the supply side, then TN-C objects go live and you could be touching that along with a true Earthed TT object from another circuit.
If it were me (who knows a bit about what I am doing) I would try to make it a bit like a UK TN-C-S arrangement where you treat the supply meter box as TN-C, then you split for TN-S (as the DNO does here) along with additional earthing and bonding of water pipes on the CPC from that point. Within your CU I would put existing TN-C circuits NE on N bar & L from MCBs, and migrate as many as you can, as quickly as practical, to 3-wire TN-S using L & N off RCBOs and the CPC to the E bar.
Yes, I should get a professional in I know, but over here, it's the wild west! Many "electricians" are very dodgy and considering what I've seen so far, I'd prefer to trust myself until I can get it checked by someone I'd trust, which I'll do as soon as I can.
I'll post pictures as I go, so that you can either shoot me down in flames or give me more excellent critical appraisal / advice .... Thanks
On this forum we cannot condone attempting work beyond your capabilities as this appears to be. Replacing a CU really is a job for a professional electrician, none of us want to hear of a fatal accident as a result.
However from what you currently have, and if that is representative of "professional" work in many cases, I can see you are between a rock and a hard place. In your situation it might be worth looking at attending a courses to learn a bit more and get some advice, or trying to find local help if they are better than whoever did this. At the very least you need to have some test tools to check stuff before you switch it, and to check it really is dead before you try to work on anything (i.e. safe isolation). A proper voltage tester / continuity tester is a critical thing to have for safe isolation. Also some half-decent socket tester, etc.