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

 

[murray2707]

I feel an armour is easier to make a tidy job of termination and looks neater inside a board. Split concentric is a fair bit cheaper per m though?

 

[Engineer54]

Most of the concentric installations that i've seen, the terminations have all been a total mess!!
If you're going to go down that route always use heat shrink breakouts and sleeving on the cables head and tails. You can use amalgamated tape on the head, but unless you have plenty of room, that too can look a pigs ear of a job too!!


At least with SWA cables, they will be protected against accidental damage along the runs of cable from the intake room to the individual apartments...

 

[spark 68]

Why would you need RCD protection if you used armoured cables ?

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.

 

[Knobhead]

So long as you don’t need RCD protection go for the split concentric.

Terminated correctly they look the dogs danglies. (Sorry E54, you don’t like the stuff, I do). It’s so much easier to handle than SWA. The sheath is as tough as old boots.

Please take care with the terminations, it’s all too easy to damage the neutral insulation.

 

[kevben]

So long as you don’t need RCD protection go for the split concentric.

Terminated correctly they look the dogs danglies. (Sorry E54, you don’t like the stuff, I do). It’s so much easier to handle than SWA. The sheath is as tough as old boots.

Please take care with the terminations, it’s all too easy to damage the neutral insulation.

what csa is the neutral & earth? In comparison to the Live?

 

[Knobhead]

The only concentric I’ve had dealing with were 35mm² solid aluminum line and equivalent hard drawn copper neutral.
Have a look on Doncaster cables web site for the CPC size.

The only time I’ve used split concentric was an office block. We normally worked to M&Q but we had exemption for this job. Due to the high loading from SMPS’s a separate CPC was run from the earth nest via the MET to each board. The incoming feed cables to the main switchboard were 4 core rather than the 3½ core we would normally have used. It was a bit of an odd bod job for me.

Working with concentric is great, you just have to be tidy in the way you break out the cable. The heat shrink boots and tubing make a great job of it.
The ones I did I used resin impregnated tape for the cable crutch. (It was a very long time ago :cyclist I don’t think you could get the HS break out boots then, if you could the company was as tight as a ducks bum and wouldn’t shell out for them.

 

[Engineer54]

So long as you don’t need RCD protection go for the split concentric.

Terminated correctly they look the dogs danglies. (Sorry E54, you don’t like the stuff, I do). It’s so much easier to handle than SWA. The sheath is as tough as old boots.

Please take care with the terminations, it’s all too easy to damage the neutral insulation.

I wouldn't go as far as saying i don't like Concentric cables, it's just that making the terminations can be a real ball's ache in tight spaces, and never look as neat as a well made off SWA.

 

[netblindpaul]

Split con is not acceptable under BS7671.
There is no more to say.

 

[Guest55]

Split con is not acceptable under BS7671.
There is no more to say.

although a great cable to work with , i've thought that for some time for no other reason than the neutral insulation being paper thin.

 

[Rockingit]

Split con is not acceptable under BS7671.
There is no more to say.

Justification for that assertion is...?

 

[Guest55]

Justification for that assertion is...?

i've a couple of ideas but i'll wait for paul to back up his own bold statement ;-)

 

[LeeH]

Maybe because there is no data to verify the design calcs?

But on the flip side of the coin the reg states use manufactures data?

 

[netblindpaul]

OK, I'll back track a little, & appoloigise, you cannot use Split Con as SWA, you have to treat it as FLEX.
Look at the make up of the cable and the requirements for an SWA.

I still don't believe it is acceptable under BS7671, but, it will take time to cross reference & I have a PLC to finish programming tonight, or at least try, before I am due to go out for dinner with the family.
Keep the thread alive & I will post the reasons later, though IIRC I have before.

 

[Andy78]

i've a couple of ideas but i'll wait for paul to back up his own bold statement ;-)

If you're thinking that he's thinking what I think you're thinking he's thinking, then I may be thinking similar things to what I think you think he's thinking. I think.

 

[guest119]

OP, where is the metering for each flat to be located?
Makes a difference to ownership of the laterals and therefor whether they come under bs 7671 or S & D regs.

Boydy

 

[Phoenix]

I have never used this (and I am never likely to) and I read this thread purely out of interest, but I seem to recall someone posting a while back (may have been Engineer 54) that split concentric should only be used in transmission work by DNO's. Have I mis-read that?

 

[Knobhead]

I’m waiting with baited breath for Paul’s answer.












You’ll probably find me in ward 4G of Nottingham’s QMC.

 

[Knobhead]

I have never used this (and I am never likely to) and I read this thread purely out of interest, but I seem to recall someone posting a while back (may have been Engineer 54) that split concentric should only be used in transmission work by DNO's. Have I mis-read that?

DNO’s use concentric cable N+E combined, PME. For large supplies they use 3 core wavecon concentric. That is a sod to work with.

Split concentric the N&E are separate by virtue of the neutral conductors each having an insulating layer.

Installed and terminated correctly split concentric is fine. If it wasn’t it wouldn’t get BASEC approval.

 

[netblindpaul]

Ok, for a start:

543.4.7 No means of isolation or switching shall be inserted in the outer conductor of a concentric cable.

So you can't isolate the N, & there are requirements where ALL live conductors must be isolated.

There are others, I'm a bit busy @ the moment so not much time to reply, sorry

 

[Silly Sausage]

543.4 refers to PEN conductors, split con is under discussion here.


addition:

543.4.7 because Earth would be disconnected.

 

[Guest55]

hmm , getting warmer with this debate now ;-)

following on from tonys post ,

pvc concentric cable was indeed developed for use by the dno's as it is lighter and cheaper than swa , flexible in the cold , and can be worked on live fairly easily as you know the live core is in the centre of the cable , making stripping it back alot safer with the power on.

which all means its great for the dnos.

the issues i have with its general use in buildings wiring is that the neutral conductors are not afforded the same level of insulation and protection as the live.
and as the earth conductors are bare anyway , it wouldnt take much in the way of abuse before you start getting crappy ins. res. readings between N & E.

all things considered though , its good stuff but its applications must be selected carefully.

 

[Knobhead]

Biff, nail on head!

Split concentric is for post DNO termination, concentric pre termination.

Handled and terminated right, its excellent cable. I’d much rather work with a 25mm S/C than the equivalent SWA.

I took a piece of DNO concentric and put a 1KV test on it. It took seven good clouts with a 2Lb hammer for it to even start breaking down. Not very scientific I know, normal test methods for me.

 

[Andy78]

Biff, nail on head!

Split concentric is for post DNO termination, concentric pre termination.

Handled and terminated right, its excellent cable. I’d much rather work with a 25mm S/C than the equivalent SWA.

I took a piece of DNO concentric and put a 1KV test on it. It took seven good clouts with a 2Lb hammer for it to even start breaking down. Not very scientific I know, normal test methods for me.

That'll do for me.
I first saw the durability of MI shown to me in this way. A live piece of 2L1.5 with a lamp attached and lit was pounded with a lump hammer on an anvil. Was flattened to about an inch wide before the cable failed.

 

[tbs1983]

we use split con in my job on street lighting. we get a lot of neutral-earth faults with it. mostly dead shorts. Tend to use SWA as much as possible now on new installs & rewires as we find it a lot more reliable.

 

[Knobhead]

we use split con in my job on street lighting. we get a lot of neutral-earth faults with it. mostly dead shorts. Tend to use SWA as much as possible now on new installs & rewires as we find it a lot more reliable.

Faults are mainly due to incorrect termination, I’ll guarantee it.

 

[Rockingit]

Never having terminated split-con or that I can recall, ever having seen it demonstrated, what is the correct/preferred method?

 

[Rockingit]

the issues i have with its general use in buildings wiring is that the neutral conductors are not afforded the same level of insulation and protection as the live.

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!

 

[Knobhead]

Split Concentric Cable to BS 4553-1 and BS 7870-3.20 | Eland

 

[Silly Sausage]

From the previous link, note...
"Other applications include sub main connections within high rise buildings"