Block of flats, supplies to flats.

[TaranCole]

Hi Guys,

We are undertaking a large development and just want to get some ideas on how others would supply each unit. There will be a rising main, with potentially a rhyfield unit on each floor in each 'zone'. We have in past projects used SWA to supply each unit, with the rhyfield unit supplying the redhead fuse, then supplying the meter, then supplying a switch fuse with the SWA Glanded in supplying the DB board in the flat.

With this project being slightly larger, we want to try and avoid using SWA and wondered if split concentric cable would be able to be used in this instance / how other people have supplied flats on larger scale projects.

Thanks.

 

[pc1966]

Split concentric is commonly used for this job but it has to be protected against penetration damage: either by being in an obvious place (surface mounted or in trunking) where nobody could be expected to accidentally nail it, or is has to be greater than 50mm from any surface likely to be nailed.

SWA has the advantage of not needing 30mA "additional protection" RCD wherever it is routed (that would be unacceptable for the supply to a whole flat) subject to the usual aspect of armour being earthed and able to disconnect on faults under 5s, etc. But you have the issue of proper cable glands for that armour-earthing, stiffer cable, and slightly poorer bend radius from generally being thicker.

As a rule-of-thumb minimum cable bend radius is often 8 * cable diameter, but you should check the manufacturer's data sheet before depending on that sort of value.

 

[buzzlightyear]

Rising main swa would be better has pc1966, if on tray through out the building not trunking.

 

[mainline]

As @pc1966 said
Split concentric should be treated like standard Twin & Earth type cable.

 

[timhoward]

Genuine question - is splitcon actually cheaper these days? About a year ago I considered it for a job and I seem to recall it costing about twice the price per meter as equivalent 3 core SWA.
A quick glance on CEF seems to confirm this is still the case, £9.35/m ex vat for 10mm split con, £4.80/m for SWA.
Or are there other sources where it is actually cheaper, as it logically should be?

 

[pc1966]

Good question about the cable cost, you would expect it to be cheaper than the same 3C SWA as same copper but no armour so less manufacturing and shipping costs.

But I have never seen it as saving anything on the usual web sites. I can see how it is easier to work with and on the DNO side with TN-C (not split) even more of an advantage.

 

[MJPD29]

Did a huge amount of street lighting installs where 16mm split con was specced om nearly every job for about 4 years until 2016. Absolute pain to get 2 and sometimes 3 into a cutout inside the door, hated it since then. Swa every time, even if it was double the price

 

[davesparks]

Good question about the cable cost, you would expect it to be cheaper than the same 3C SWA as same copper but no armour so less manufacturing and shipping costs.

But far more 3c SWA is used by the average electrician than splitcon, so your usual wholesalers will be buying far more SWA so will get far better prices on it.

It's economies of scale in action.