Split concentric submains

[kevben]

I am currently on a big flat development project (old high school being converted to 50 flats, plus a 3 phase landlord supply). I had planned on installing 25mm 3core SWA for all flat submains as the Flats are all Electric with no Gas.
However, i am now considering installing 25mm or 35mm split concentric cable as the installation method would not require RCD protection.
It seems to me to be an easier option when it comes to termination at both: the supply Main Fuse (installed via trunking at the Bemco Cupboard) & at the Flat Consumer Unit.
The area that has been designated for the Bemco Cupboard (for all 50 x Flats etc) is extremely small, hence the potential option of installing split concentric cable versus SWA.
I have come across this method of submain installation on many occasions but have i never personally installed it.

I would appreciate any advice regarding using split concentric cable & also the current capacity of such cable (some flats will be approximately 120m cable lengths).

Thanks - KevBen

 

[Guest55]

Apart from the obvious one of the live being itself 'protected' by N & E, I can't see how that really stacks up? You've a 7 stranded core covered in one layer of insulation, and a N of 7 x singles (or small stranded) all individually wrapped to produce the same csa - so on aggregate that's far more PVC covering the N than the L!

because the insulation covering the neutral strands is a quarter of the thickness of the live core and can be stripped off with a nothing more than a fingernail - ie , its very thin & weak in comparison.

get a piece and strip it as youve never terminated the stuff. ;-)

 

[Rockingit]

because the insulation covering the neutral strands is a quarter of the thickness of the live core and can be stripped off with a nothing more than a fingernail - ie , its very thin & weak in comparison.

get a piece and strip it as youve never terminated the stuff. ;-)

OK, I will! If someone would like to give written instructions on how it should be done, I'll happily get the bits in to do it, give it a first go with pics, and you can all peer review!! See.....got big ones, me.

 

[Guest55]

its a doddle.....


strip back outer pvc and inner clear selophane wrapping to reveal thus.........



twist together neutrals into 1 bundle & sleeving over earth strands
heat shrink pvc boot can be inserted over the base of cores if youre feeling flash
and cable entry is nothing more extravagant than an IP stuffing gland & shroud.

;-)

 

[Rockingit]

its a doddle.....


strip back outer pvc and inner clear selophane wrapping to reveal thus.........

View attachment 21198

twist together neutrals into 1 bundle & sleeving over earth strands
heat shrink pvc boot can be inserted over the base of cores if youre feeling flash
and cable entry is nothing more extravagant than an IP stuffing gland & shroud.

;-)

LOL - and here was me thinking I'd be needing to get the spanners out!! In which case, I think I got it covered. :cowboy:

 

[Guest55]

i'd have finished and gone home while you went for the spanners

 

[netblindpaul]

OK, I am too busy to try to find the reference, & thus I will give in, and apologise & say that I can't find the reference to limit the use of split con, but I thought it had come in recently with the last red or green books.
SORRY, it looks like I was wrong, as my memory has failed me, again.

I only have the latest book in electronic format to run a search on, but, if it came in on the red it should still be there.

So, I'll say I was wrong to say it CAN'T be used, but, I will not back down on it being treated as flex, as it does not have an earthed outer, thus it cannot be used in the same manner as SWA.

SO, if you are going to use it in an area where an earthed outer is required to negate RCD protection for example, then you can't, as the N cores are wrapped around under the sheath and are still classed as live conductors, so you can't bury it in walls for example and say that you don't need an RCD in the same way you can with conventional SWA.
The N cores do not have an earthed outer to protect them.

IF I can find the reference(s) I was hoping to, IF I ever have time, I will try, to remember to post it/them.

Sorry.

 

[Knobhead]

its a doddle.....


strip back outer pvc and inner clear selophane wrapping to reveal thus.........

View attachment 21198

twist together neutrals into 1 bundle & sleeving over earth strands
heat shrink pvc boot can be inserted over the base of cores if youre feeling flash
and cable entry is nothing more extravagant than an IP stuffing gland & shroud.

;-)

Personally I would have put a heat shrink on the both the CPC and neutrals, then tightly bind the crutch with amalgamating tape.

To tape the crutch properly the CPC and neutral have to first be layed at 90° to the line conductor. Each set of conductors twisted to the natural lay of the cable and then heat shrink applied. It’s a good idea to also heat shrink the line. Tape up using ½ lap to form a tight seal.
Looks mint and is a dammed site smaller than a heat shrink boot.

 

[Engineer54]

its a doddle.....


strip back outer pvc and inner clear selophane wrapping to reveal thus.........

View attachment 21198

twist together neutrals into 1 bundle & sleeving over earth strands
heat shrink pvc boot can be inserted over the base of cores if youre feeling flash
and cable entry is nothing more extravagant than an IP stuffing gland & shroud.

;-)

All looks so easy and simple to terminate when shown like this... In reality, in tight locations, and it can be anything but easy and simple. As i say, most of the final terminations to this type of cable that i've seen, have been a real pig's ear!!

Oh and personally i'd never even contemplate using any unarmoured concentric cable in a direct burial installation, only when ducted!!

 

[Silly Sausage]

As i say, most of the final terminations to this type of cable that i've seen, have been a real pig's ear!!

You've got to stop working with amateurs Eng! :smilielol5:

 

[Knobhead]

All looks so easy and simple to terminate when shown like this... In reality, in tight locations, and it can be anything but easy and simple. As i say, most of the final terminations to this type of cable that i've seen, have been a real pig's ear!!

Oh and personally i'd never even contemplate using any unarmoured concentric cable in a direct burial installation, only when ducted!!

Where did direct burial come from?

As far as a remember we are talking of internal wiring with sufficient depth to negate RCD protection.

Regarding making off in a restricted space, it’s no worse than SWA.

Going back to DNO concentric, I’d pit it against a SWA when attacked with a pick and shovel.

 

[guest119]

Pick, shovel, 2lb hammer?
What are you like Tony? :86:

Boydy

 

[Knobhead]

An animal.

Comes as natural in my former walk of life.

I’m not bad with explosives and a thermic lance.

 

[Engineer54]

Where did direct burial come from? Your post 29 (suppliers cable description!!)

As far as a remember we are talking of internal wiring with sufficient depth to negate RCD protection.

Regarding making off in a restricted space, it’s no worse than SWA. Give me a SWA cable over a Concentric cable in a tight space every time!!

Going back to DNO concentric, I'd pit it against a SWA when attacked with a pick and shovel.
Now you're taking the ****!! lol!!!

So what's different about DNO concentric cable, to those that are available to all?? As far as i can see there is only two BS standards covering concentric cables. Pretty sure they don't produce a concentric cable purely for the DNO's, that would cost the DNO's an arm and a leg for special cable....

 

[Knobhead]

From the same web site.

Application: Split concentric cables are largely used by Distribution Network Operators (DNO) for providing final service connection to customer properties. Other applications include sub main connections within high rise buildings and street light systems. The cables are designed for direct burial and the polymeric covering of the Neutral conductor ensures greater corrosion resistance.

On a submain it is perfectly acceptable practice to use this cable.

For a buried non DNO submain it must be protected by some mechanical means. IE ducting.

DNO's don't work to BS7671. Split concentric conforms to their requirements as well as BASEC.

I'm fed up with this argument, it's going round in circles. I'll bow out now, I can't/won't argue futher.

 

[Engineer54]

From the same web site.

Application: Split concentric cables are largely used by Distribution Network Operators (DNO) for providing final service connection to customer properties. Other applications include sub main connections within high rise buildings and street light systems. The cables are designed for direct burial and the polymeric covering of the Neutral conductor ensures greater corrosion resistance.

On a submain it is perfectly acceptable practice to use this cable.

I didn't say it wasn't, but i wouldn't use any unarmoured cable in a direct burial situation, this cable is far better installed in a Duct...