When I had my own electricity supply added to my workshop about 35 years ago, the LEB told me where to dig a hole on my side of the wall facing the street and they dropped me round a big metal spike. My mate who worked for the LEB at the time told me to hammer it into the ground for the earth. I did that and he checked it and said it wasn’t great so he gave me another one that screwed on to the original and I hammered that in too. Must have gone down at least 6 feet. Still wasn’t great but he said 'that will do'!
When you think about it, you've put in less than 2m of a relatively small rod - so not much contact area. That's why I'm thinking that utilising the trench would give me significantly larger contact and dispersal area.
This is what was done where I worked at the Point of Aye gas terminal, there was a large physical size resistor about the size of a small van between the TN-C-S supplied earth and the site earth, to limit the current in the earth cable should there be a loss of PEN, and this is the problem, with a simple earth rod, between 2 and 6 at 1.2 meters were required to get 8Ω and 230/8 = 28.75 amps which is not really a problem for a 6 mm² cable, but with an earth mat you could get 0.8Ω so 287.5 amp, and this would melt the cable under fault conditions.
I have a family member who works for a DNO. He once gave dad and myself a tour of the local 132/33/11kV substation. He did mention that they use a large earth grid across most of the site - which I suspect will be in part to avoid the potential (no pun intended) to have dangerous voltage gradients where people might be working. And yes, a big neutral earthing resistor between a transformer star point and the earth grid.
He also mentioned that they have had problems with the earth grid being ripped out by thieves - along with various other metal thefts.
IF you have a trench, then look into the condudisc - Flameport can tell you more about how good they are.
I've heard of those before. I suspect
Conducrete would be a better fit for this project. I do find myself wondering if it's one of those "if you have to ask the price, you can't afford it" kind of things.
You could always use the house earth.
It was really a case of - I'm digging a trench, so apart from the cost of materials there's almost no effort in adding a significant earth electrode. A couple of things make me think of this :
* That there was at one point an expectation that it would become a required thing for BS7671 - so putting one in now would avoid needing to try and drive a rod later.
* Discussions regarding lost PENs. SWMBO keeps an eye on someone's cottage while they are away - and one day they had no power. I didn't have any tools/meters with me, but following the overhead wires back, I'm fairly certain it was the PEN that was broken at the top of the pole - 3 poles along and after at least one other property was connected. We have underground services, but still scope for it.
* At some point I guess we'll end up with an EV of some sort - and hence a charge point.
* And I did have in mind that (depending what I put in) it could also serve as the CPC to the shed supply, giving me more options in terms of what cable I pull through the duct later - does anyone make concentric with the outer layer all blue insulated ? I can't think of any reg that would prohibit that.