Insulated tails used to supply flats

It may just about be OK, if the cables are on view, or so deeply buried as to be not likely to be disturbed, 50mm deep or more from the surface is normally considered OK.

Another issue to ponder is that T and E normally has a reduced earth core compared to L and N, and may not be enough cross section to serve as the main earth in the flat, depending  if things like water pipes main bonding is at the flat end or done centrally at the building incomer.

Steel wire armoured cable or in earthed metal trunking of some kind would be much preferred. An RCD at the origin is not very convenient if the flat and the RCD are separated by any distance even less so if the RCD is in a locked meter cupboard.

Also SWA or similar 'hard to access the live conductors' arrangements are usually preferred when the meters are at the consumer's end - simply to discourage 'abstraction' - if the meters are at the intake end it's less of an issue.

  - Andy.

Thanks both, was there not an amendment in 2015 requiring all cables in the building fabric to be protected by armour or RCD, I’m sure I saw it somewhere, the 50mm rule has been in since the 17th I think?

This is what I read.

https://electrical.theiet.org/wiring-matters/years/2015/54-special-edition-2015/rcds-protection-of-cables-concealed-in-walls-or-partitions/

Yup - note the "concealed in walls or partitions" in the title.


Actually I think the basic requirement has been there since 2008 (start of the 17th) - the amendment just took away the option to omit RCD protection on sites that were under supervision of skilled or instructed persons (a change which hit a lot of commercial premises).


Surface cables (whether soft sheathed or in insulating conduit etc) still don't have an RCD requirement .... which is pretty handy given that most meter tails are PVC/PVC.


  - Andy.

The way I explained this to our electrical supervisor was that the supply cable entering the flats distribution board would have to be metal conduit protected if its flush fitted, if the board is fitted to a wall the supply cable will be in the wall...

Is that me being pedantic or is this why all our new sites use armoured cables for supplies?

The last consumer unit I replaced in a block of flats was in Cardiff, the flats were built in the 1990’s and the supply from the intake to the flat is 16 mm twin and earth with a full size insulated earth conductor, don’t assume all 16 mm twin and earth has a reduced size CPC without having a look at it.


 Andy Betteridge

The way I explained this to our electrical supervisor was that the supply cable entering the flats distribution board would have to be metal conduit protected if its flush fitted, if the board is fitted to a wall the supply cable will be in the wall...

Is that me being pedantic or is this why all our new sites use armoured cables for supplies?

In general yes, but the details might catch you out. If the CUs are flush and the cable route hidden then there might be some earth steel conduit for the little part of the run to the floor or ceiling - presumably it's not easy to tell now. There's no need for the rest of the run (on the surface, under floors, above ceilings or deep in walls) to have the same treatment. There again if the CU is flushed into a decent sized void then the cable might be more than 50mm from the surface - so again side-stepping the need for RCD protection. Commonly CUs are surface mounted of course - so surface mounting the supply cable (usually in a bit of PVC trunking to make it look a bit less ugly) is quite popular, especially where it's hidden away in a cupboard.  Without seeing it, it's hard to tell - for sure the cables might be shallow and the RCD requirement overlooked, but there again it might not.


Certainly specifying SWA makes life an awful lot easier - the cable can then be run (almost) anywhere you like and conformity is just about guaranteed - and won't be called into question if things 'on site' don't go exactly to plan or if an inspector can't see everything - but that doesn't mean that the older methods are necessarily wrong.


   - Andy.

Dosent the 2015 amendment mean the 50mm protection is no longer relevant?

Not really, see the article you linked to further up this very thread.

As it says in so many words, soft skin cables that are shallower than 50mm, need RCD protection and to be in the zones.

Cables deeper than 50mm, or at any depth protected by earthed armour, or trunking, or whose routes are not concealed, can be routed anywhere, and  do not need RCD.