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.

 

[westward10]

It is a concentric cable.

 

[1Justin]

I was tempted to call it "concentric". I'm only previously familiar with domestic 1 Ph supply TN-S which splits N & E on the outer.

 

[westward10]

If your cable has all bare outer cores then it is concentric where these cores form a PEN conductor. If some of the cores are sleeved blue or black then it is split concentric. Concentric is commonly used for TN-C-S supplies with split concentric used for SN-E supplies or in old money TN-S.

 

[1Justin]

Definitely concentric. Not split. I'd hesitate to call it P"M"E because there is definitely no opportunity for any multiple earths this side of the substation.

 

[westward10]

It isn't PME. Don't forget TN-C-S doesn't necessarily mean PME as you say is is not protective multiple earthed so it is either TN-C-S or PNB.

 

[R-fur]

You said it comes a private substation? You have to get home office permission to have a TNC system the electricity ccompanies have blanket permissions but belive it has to be more specific for private installations. Does this instalation have permission? You said the cable was DNO installed why were they working on private network? If they were working as a contractor the installation should have been done to the current regs.

 

[westward10]

I agree I have overlooked the "private" part. Most private transformers use a separate neutral and earthing conductor often bonded together at the installation or left separate.

 

[Simon47]

Just on a matter of semantics and words ...
Cold "private" really mean "DNO owned but only serving this customer" ? At a previous employer we had this - "our own" substation feeding just our site, but it was DNO owned and things only became ours when the cables came through the trench under the wall and into our switchboard.
So I assume to many it would be a "private" substation - but in reality it's just another DNO owned substation that happens to be on the customers site, in a building the customer built, and serving only that customer.

 

[westward10]

@R-fur is more versed in these matters than me but I would say the DNOs involvement stops at the transformers primary.