Strange SWA cable

[oldsparky99]

I've just moved into a 1960's house and when checking the supply to the detatched garage I came across a strange cable type that I at first thought was SWA. It's 10mm diameter with a black plastic sheath. There is one core of 7 strands with red pvc insulation, 7 strands individually insulated with black pvc and 7 bare strands. The 7 individually insulated strands have all been connected together and used as the neutral. There is no armouring and all conductors are copper. Anyone seen this type of cable before ?

 

[Pete999]

I've just moved into a 1960's house and when checking the supply to the detatched garage I came across a strange cable type that I at first thought was SWA. It's 10mm diameter with a black plastic sheath. There is one core of 7 strands with red pvc insulation, 7 strands individually insulated with black pvc and 7 bare strands. The 7 individually insulated strands have all been connected together and used as the neutral. There is no armouring and all conductors are copper. Anyone seen this type of cable before ?

Concentric cable maybe?

 

[westward10]

Concentric cable maybe?

Split concentric.

 

[Leesparkykent]

Yeah as above split concentric.

 

[westward10]

It isn't a common cable to be used on a supply to a dist board but you do come across it. The other type is concentric where the neutral and cpc are combined in one conductor (PEN) and is used by supply companies for TN-C-S supplies, this should not be used in the situation you have.

 

[freddo]

Split con is awesome cable as it is light and easy to install, unfortunately it is not permitted for many applications.

 

[westward10]

Split con is awesome cable as it is light and easy to install, unfortunately it is not permitted for many applications.

Why not?

 

[oldsparky99]

Thanks for your help guys. It's 4mm split concentric. Looks like it was run through a pvc pipe for the buried section between the house and garage and overall seens to be a good job, unlike some other finds in the house like wall light fed with bell wire direct from the back of sockets!

 

[Leesparkykent]

Why not?

Probably because cant be buried in a wall at a depth of less than 50mm with out mechanical/earthed mechanical protection or metal partition walls if 30mA RCD protection wants to be omitted.

 

[freddo]

As above, which is a shame as it's great for use as a submain cable, with such a small OD compared to other cables.

 

[westward10]

Probably because cant be buried in a wall at a depth of less than 50mm with out mechanical/earthed mechanical protection or metal partition walls if 30mA RCD protection wants to be omitted.[

Yes I suspected this as the answer, I could be wrong but under the 16th Ed this type of cable could be used without additional protection, come the 17th it was omitted from the list.

 

[freddo]

Bloody stupid 17th edition.

 

[Leesparkykent]

Yes I suspected this as the answer, I could be wrong but under the 16th Ed this type of cable could be used without additional protection, come the 17th it was omitted from the list.

Yeah same as all the 16mm T&E used to supply thousands of flats across the country which is a bit hard to use now without additional protection or a lot of extra effort to make it comply for the same application. DNO use split con still though buried direct in the ground IIRC

 

[DPG]

I can still never work out why the DNO are allowed to bury a split-con from the road to your house when it has no armouring and no RCD protection. I know they don't work to 7671 regs but surely it's quite a hazard. A spade easily goes through it.
Daz

 

[freddo]

Shhh! Or we will end up with the supply transformers being fitted with 30mA RCDs on their output! The outer earth or earth and neutral surrounding the live core or cores makes it more than safe enough, as you will hit the 0V conductors first.