Earthing system question please???

[bartkusal]

Hello, I wonder if there is anyone here to help me out. Thanks in advance for the help.
Ok. I am doing electrics on 6 metal containers in community fields( I know, I don’t like them metal boxes too), I got it all under control, but there is little thing what buggers me. I kind of finding trouble working out the earthing arrangements. I know, stupid me, forgot to take the pictures, but the picture in words is:
From the first view it seems like TN-S (it has the earth cable coming out from the sheathing of the incoming supply cable, but on closer look I found that it has another earthing cable coming to MET, and when traced,I found it attached to the rod, so maybe TT then.
Measured Ze from the sheath only, it came up as 0.25 ohms (lovely),measured from electrode only, it came as 525 ohms ( up’s), measured them both together, it came as 0.27 ohms. Lookslike rod is worsening the Ze for me. I thought just to get away with the rod,but something not right here, because I Have the 30 mA RCD before the whole installation too, which is strange too.(100 mA would be sufficient and then down to 30 mA on the final circuits)

So my questions are:
· What earthing arrangement I have:
· TN-S (earthing from sheath)?
· TN-C-S( some sort of converted and because is so low reading)
· TT ( as per earth rod and RCD )

Thanks again for your input guys, and I need it sort of ASAP, started today and planning to finish on Friday, so realy need to work this out.

 

[bartkusal]

Well the only DNO cable i know where the earth comes directly off the sheath, is the older PILC cable. These days the DNO's's will use Split concentric cables in there legs up to the TN-S service heads. I doubt these pillars have been in place since the time of PILC's, so i'm a little confused now. Shame you can't post a photo or two. A picture can explain many questions... lol!!

thanks for reply, i dont think it is PILC, there is no lead sheath, probably it is more like split concentric as you say becouse of the fine copper strands visible on the sheath, I promise to do pics tomorrow.