DNO connection

Not a great deal of confidence in this earth connection. Below a footpath about to be back filled with quarry dust

I've seen few line that (both LV and HV) - seems to be standard practice and I can understand not wanting to hammering it deeper when there could be all sort of other cables & pipes below.


It's likely "only" an additional electrode anyway - so probably not catastrophic if it's a few 10s of Ohms (or even a few 100s of Ohms) higher than ideal. (Even a say 20Ω rod isn't going to make a significant difference to a broken PEN situation unless the cable is only feeding a very small load, such as a solitary street light)


    - Andy.

on its own it mite not be up to much but I bet in parallel with a few others its a respectably low value

It makes me wonder why the DNOs do not put in an earth rod (or tape or mat) every time that they make a junction. It would not cost much.


I believe that it has been WPD's policy for about 5 years now and they have a standard length of solid copper wire about 1.5 m long that looks as if it has been Thermit welded to a rod. It is made off in the joint and as Lyle's image shows, laid horizontally in all the joint jobs I've seen.


Regards


BOD

It may well be a hundred ohms or so of N-E 'electrode' On its own you might just about keep the lights on in a bus stop, in a PEN fault. But the idea of the electrodes is not really to provide a solid return path for normal load currents, like some low voltage version of a single wire earth return supply. Rather it is just to keep neutral near terra-firma potential when all is well,  and provide some back up  if the is a failure of what would otherwise be the one and only earth connection at the substation.

The other advantage of a horizontal electrode is that there is not such a sharp step voltage gradient on the surface during faults, (voltage contours being more ecliptical than point like) Under a footpath that is moot, but I guess if the rule book says do this, they do it every time.


M.

That was my thought - isn't the idea of PME that loads of electrodes help to keep N at E potential?

Given the resistances involved, I rather suspect it's more effective at keeping a small portion of the ground at N potential, rather than having any significant effect on the voltage on the N itself.

   - Andy.

Here is a radical idea. What about use of 4 core cables with a black neutral core, and red, yellow, and blue cores for the three phases. covered with PVC or similar insulating materials.

Provide an outer sheathing of galvanised steel wires. This would serve three purposes. Firstly the robust wires would protect the insulated cores from damage. Secondly the steel wires would provide a metallic earth path back to the transformer. And finally, these metal wires would be in contact with the general mass of earth, thereby providing a very low resistance to earth.

broadgage not very easy to work on the cable live though is it.

Provide an outer sheathing of galvanised steel wires. This would serve three purposes. Firstly the robust wires would protect the insulated cores from damage. Secondly the steel wires would provide a metallic earth path back to the transformer. And finally, these metal wires would be in contact with the general mass of earth, thereby providing a very low resistance to earth.


How long would the bare metal in contact with earth last before corrosion, even if galvanised? Most "galvanised" products you see these days is barely zinc plated, yet alone hot dipped............


Regards


BOD