EICR. Cu "armoured" 3Ph supply cable. Is this a thing?

[1Justin]

I've come across a DNO installed (SSEN) 3 Ph 3 core PNE supply cable from a private substation to a large Lucy domestic head. Cable 3 Ph is copper "armoured" (or is there a better name for it?). Entirely underground, entirely within a domestic single owner property. No obvious practical or visible locations for any intermediate earthing, it's a PNE supply, earth breakout in the head. It dates from ~ 1989.
I was not aware before this that copper "armoured" (or might it be called concentric since it's not armour) was a thing? Cable is Pirelli. Marked 6-60 with 3 cores and about (my my careful measurement) about 60mm^2 of CU in the outer NE conductor.

 

[R-fur]

I'm confused by this, but it likely I'm misunderstanding you. Most of our privately owned transformers have four cables coming of the secondary side, 3 phases and neutral. The earth neutral link is introduced in the LV distribution panel down stream.

DNO substations normaly have a fuse cabinate mounted on the transformer the N/E is in there. What you describe is normal for private networks and is still classed as TNS. People get confused by this as most text books show the starpoint of the transformer being earthed, this is rarly done.