Sub Board Problems - Advice Needed! -

[scorpiolight]

My first post as I always find what I want (up till now) Hope someone can help.
I have been asked to fit a 3P socket from a sub board that is fed from a 3P 24 way board 70 meters away. The main board is a PME (0.12) but the sub board is located on the wall of a steel container sitting on the ground and the main earth is 16mm looped from the terminal to the bolt that secures the sub board to the container wall and there is a sticker that says "TT <1667.(Its actually 0.76) I have quoted for running the cpc back to the MET but have met with the usual problems due to cost. I have never come across this before, I was amazed but I dont do a lot like this and cant find it in the Regs. Can anyone shed any light?, is this acceptable practice (in the yard of a heavy vehicle storage facility).

 

[Des 56]

A steel container remote from the supply could be likened to a caravan which doesn't permit pme
There is the potential of standing on ground and grabbing say a metal handle of that steel structure

What type of ground is this container standing on and what is the supply cable at present and is the shed main bonded with a core of the supply cable perhaps.Is there Rcd protection at the sub board
Is the container itself being used as an earth electrode to minimise any potential difference locally

 

[scorpiolight]

The container is on bare earth with a concrete slab at the entrance. The entire container, including the entrance handles are steel (ex shipping container). It also contains a SP lighting circuit and a 3P supply to compressor from the sub board.
The supply cable is 4mm 4 core SWA (3+N) , there is No RCD protection anywhere on the installation.

I see the principle of using the container as an earth electrode to minimise the potential but why do that in preference to PME it other than a cost saving?

I never thought of the caravan, interesting and a possibilty.

Thanks for your Interest.