Concentric wiring

[swifters]

Could someone please explain to me a bit about concentric wiring? If you can't utilise an RCD as TLC direct claim below then how do you meet requirements of 17th edition??? Are they just talking about a combined neutral and earth concentric wiring? I imagine you could still use a RCD with concentric wiring that has a line, neutral and external concentric copper conductor encasing both line and neutral?

"Earthed concentric wiring may only be used under very special conditions, which usually involve the use of a private transformer supply or a private generating plant. Since there is no separate path for earth currents, it follows that residual current devices (RCDs) will not be effective and therefore must not be used. The cross-sectional area of the sheath (neutral and earth conductor) of a cable used in such a system must never be less than 4 mm² copper, or 16 mm² aluminium or less than the inner core for a single core cable. All multicore copper mineral insulated cables comply with this requirement, even a I mm² two core cable having the necessary sheath cross-sectional area. However, only single core cables of 6 mm² and below may be used. The combined protective and neutral conductors (sheaths) of such cables must not serve more than one final circuit.
Wherever a joint becomes necessary in the PEN conductor, the contact through the normal sealing pot and gland is insufficient; an extra earth tail must be used as shown in {Fig 5.19}. If it becomes necessary to separate the neutral and protective conductors at any point in an installation, they must not be connected together again beyond that point."

 

[Knobhead]

Only ever had the chance to use it on one job. Six sub boards in an office block. After being used to nothing but SWA I fell in love with the stuff, so easy to work with.

 

[Guest55]

Are you suggesting that the insulation on the neutral conductor is not satisfactory?

Not at all , i find pvc split con great to work with , but it was originally developed for use with DNO supplies which work to different regulations , not domestic installations.
Therefore a bit of thought is needed before using it.
Plus the fact that it may need rcd protection whereas swa does not limits its uses somewhat.

 

[Engineer54]

Depending on the size of split concentric cables, i bet the majority of the final terminations look like a pig's ear of a job!! There is to my view, only one means of terminating these cables that will make them look anywhere near decent, and i doubt very much if that method is used in even 1% of this type cable terminations... lol!!

 

[Knobhead]

If you have any pride in your work then it needn’t look a “pigs ear”. I could take exception to your comment, but I won’t.

 

[Engineer54]

If you have any pride in your work then it needn't look a “pigs ear”. I could take exception to your comment, but I won’t.

Not sure why you would take exception to my comment, as you could probably do a more than decent job using amalgamating tape, as well as with a 3 leg heat shrink breakout.

But in all honesty, how many of these new electricians could?? Come to that how many would even try!! lol!!!

 

[Knobhead]

I used heat shrink tubing but couldn’t get the correct boots so used a larger tube to shrink over the crutch area.
It made a nice change to not be working to M&Q.

 

[chrislee765]

How do you terminate these split concentric sub-main cables??

Using a 3 way cable breakout. It slips over the end of the split concentric, separates the conductors and then heat shrinks down. It's got a glue inside that melts once heated and makes a very permanent termination.
It looks neat, but nowhere near as neat as an swa gland.

edit:
Hmm I was far too slow here, didn't notice there was a second page. Oops!

 

[SparkyJoe]

you can do a decent job with some small tie wraps, a lot of the new build housing i was working on was done with it for the sub mains.

 

[Spudnik]

Are you suggesting that the insulation on the neutral conductor is not satisfactory?

Like every wiring system, there are applications where specific cables can be used. I see no reason why split concentric cable cannot be used by non-DNO for sub mains installations. It is never suggested that it is an armoured cable and should not be treated as such.

I personally use it for the majority of domestic sub-main installations, where appropriate. The reason I do is because I find it much more flexible and therfore easier to work with than SWA.

100% agree and do exactly the same.

Brilliant stuff.

 

[mogga]

it was and might still be popular on street lighting installs where if doing 2 or 3 into an SMK cutout you have no opotion but to make your ends off as neat as possibl epersonaly id use pvc tape due to space and never getting heat shrink The training we got used loose fitting sleeving on the N E cores making for a pish looking job

 

[Engineer54]

you can do a decent job with some small tie wraps, a lot of the new build housing i was working on was done with it for the sub mains.

Honestly, ...tie wraps?? lol!! Oh Dear!!!!

 

[SparkyJoe]

Honestly, ...tie wraps?? lol!! Oh Dear!!!!

Yup. Nout wrong with little tie wraps :|

 

[Engineer54]

Yup. Nout wrong with little tie wraps :|

Maybe only in your world!!!....