Split con cable for sub main?

[prospark]

Hi folks,

interested in opinions for the use of split concentric cable BS7870 for use as sub main to garage or loft conversion within a domestic property.
Also were can i find a guide to current ratings as they dont appear in the regs tables or my basic cable calc

many thanks

steve

 

[mechelec]

Fine to use, smaller than equivilent SWA but may need RCD/mechanical protection depending upon installation method. You would be best using compression glands when terminating into the CU.

 

[mogga]

possibly better to use a bit of 4x2 trunking as a "spreader" terminating into a smaller consumer unit with not much space And as already said RCD,Mechanical protection will be required

 

[Engineer54]

Basically a supply company cable, who have a different set of rules to comply with than you.
You will need to provide some form of mechanical protection if your intending to run this type of cable underground, such as providing a duct etc....

As for a loft conversion?? Not someone else that's going to install a CU for a bedroom!!!

These concentric cables can be a pig to terminate, without it looking like a pig's ear of a job. The best way i know is to use a 3 spout heatshrink breakout, to hide the separation or the concentric strands into cores....

 

[Spudnik]

AS above.

It can be a pain to terminate, but nowhere near as a pain as the equivalent SWA!

You MUST treat the cable as if it were T&E and RCD protect where required.

 

[Knobhead]

It’s nice stuff in the right environment. But as E54 pointed out with out the heat shrink termination it can look rough, it can be made to look good without, but it’s time consuming.

 

[Engineer54]

And how good you are with the amalgamating tape! lol!!

 

[mogga]

Basically a supply company cable, who have a different set of rules to comply with than you.
You will need to provide some form of mechanical protection if your intending to run this type of cable underground, such as providing a duct etc....

As for a loft conversion?? Not someone else that's going to install a CU for a bedroom!!!

These concentric cables can be a pig to terminate, without it looking like a pig's ear of a job. The best way i know is to use a 3 spout heatshrink breakout, to hide the separation or the concentric strands into cores....[/Qa lot od L.As use it on street lighting as its cheaper than swa and if ducted correctly it is replaceable
BUT making it look good in an SMK cut out isnt the easies thing to do

 

[Knobhead]

And how good you are with the amalgamating tape! lol!!

I’ve not done many of them but never used tape. Just dressed and laid each of the neutral / earth cores to perfection.

I’ve dressed 200 pair cables without a single bit of tape or a tie anywhere (on show). I’d dread to do one now, I haven’t the patience any more.
OK I’m a grumpy old sod!

 

[Engineer54]

I’ve not done many of them but never used tape. Just dressed and laid each of the neutral / earth cores to perfection.

I’ve dressed 200 pair cables without a single bit of tape or a tie anywhere (on show). I’d dread to do one now, I haven’t the patience any more.
OK I’m a grumpy old sod!

No Not grumpy, ...i wouldn't have even tried doing that, on the few occassions i've dealt with these concentric cables, i've always used a 3 spout break-out and heatshrink sleeved the two bound concentric cores into conventional cores. It's about the neatest way i can think of terminating this type of cable, you can make it look a pretty decent job too!!! lol!!!

 

[prospark]

thanks for the comments,but me thinks i will stick with swa or T & E, sounds like too much hassle, and no i wasn't going to install a consumer unit for a bedroom.

 

[duffsparky]

Uhhh why does it need to be ducted if installed underground? I don't believe BS7671 (any version) calls for it. However, if it's a single phase cable e.g. single core with spiral neutral outer then there is no cpc cover which 7671 calls for, unless that is you work for the lecky companies.

 

[Engineer54]

Uhhh why does it need to be ducted if installed underground? I don't believe BS7671 (any version) calls for it. However, if it's a single phase cable e.g. single core with spiral neutral outer then there is no cpc cover which 7671 calls for, unless that is you work for the lecky companies.

So where is the Mechanical protection to allow it to be installed in a ''direct buried'' manner??
The DNO do not follow BS7671 for it's local network distribution, they have there own rules to follow, ...You however need to follow BS7671, It doesn't matter a jot if it is single phase three phase, with a neutral, with, or without a CPC, it will need installing in a duct of one sort or another, when routed underground!!

 

[duffsparky]

So where is the Mechanical protection to allow it to be installed in a ''direct buried'' manner?? The DNO do not follow BS7671 for it's local network distribution, they have there own rules to follow, ...You however need to follow BS7671, It doesn't matter a jot if it is single phase three phase, with a neutral, with, or without a CPC, it will need installing in a duct of one sort or another, when routed underground!!

As far as I remember, one only has to consider the ground type and depth the cable is installed in relation to the use of the ground ie if it's shallow then mechanical protection is advisable. Plastic ducts do not really provide mechanical protection except from the immediate ground makeup ie sharp stones. A pick axe or JCB will go through a plastic duct very easily; interlocking paviors would provide better mech protection. The duct, unless required for protection against immediate ground make up, is there more for ease of installing cables after the duct has been laid and the trench back filled. I have laid thousands of metres of cable in the ground, quite often laid in a bed of soft sand, without a duct in sight, however, given the choice I would always install one. I'd be interested to know which BS7671 regs states a duct must always be used where cables are burried in the ground??? My reference to single phase splitcon cable is perhaps badly worded, it has to do with the absence of an earthed shield; assuming that is it's an not armoured type. If using a multi-core splitcon cable where the outer conductor is not required for neutral then this outer core can be earthed to comply with the regs requirements.

 

[Engineer54]

As far as I remember, one only has to consider the ground type and depth the cable is installed in relation to the use of the ground ie if it's shallow then mechanical protection is advisable. Plastic ducts do not really provide mechanical protection except from the immediate ground makeup ie sharp stones. A pick axe or JCB will go through a plastic duct very easily; interlocking paviors would provide better mech protection. The duct, unless required for protection against immediate ground make up, is there more for ease of installing cables after the duct has been laid and the trench back filled. I have laid thousands of metres of cable in the ground, quite often laid in a bed of soft sand, without a duct in sight, however, given the choice I would always install one. I'd be interested to know which BS7671 regs states a duct must always be used where cables are burried in the ground??? My reference to single phase splitcon cable is perhaps badly worded, it has to do with the absence of an earthed shield; assuming that is it's an not armoured type. If using a multi-core splitcon cable where the outer conductor is not required for neutral then this outer core can be earthed to comply with the regs requirements.

I've seen SWA penetrated far too many times by sharp stones and other debris to even consider laying a non armoured cable in the ground at any depth, with or without sand bed and blanket. At least with an armoured cable if the sheath gets damaged during or after cable laying it's only going to be subject to corrosion problems, as bad as that is, it's not as bad as when penetrating the neutral or phase conductor!!

All our cable trenches, be they for ducts or direct buried cable will have cable tile and marker protection. Like yourself i am no stranger to burying cables, we are at the moment in the process of laying more than a good few thousand metres of MV and LV main and sub-main supply cables. Most of the LV being paralleled cable runs too. The MV cables for the most part, are installed in a ducted distribution system.


I don't have anything with me at home, but i'm sure there is some reference in the Reg's to mechanical protection for direct buried cables... As has been said, you can consider concentric cables as little more than T&E when it comes to direct burying them...