25mm t&e???

[brs73]

hello there
i've been squabbling with my pal about two supplies we have to put in for somebody.
edf are putting in new meters and we have to supply 2x 2 bed flats
i reckon you have to run 2x 25mm swa cables to each flat. (very difficult route)
my mate reckons you can run a 25mm t&e to each one but i thought it had to be swa.
if you was to run t&e with a 63a rccb protecting it would it be acceptable.
the flats have recently been split into two and renovated but they only want to sort out the metering problem now.
the cable will be running through floor joists and ceilings and hopefully boxed in in places
any advice would be greatly appreciated
also could anybody direct me to the relevent regulation/guidance that clarifies this
thanks all
good luck

 

[sparks1234]

Why would you run 2 x SWA,

are the cables running through communal areas? do they need mechanical protection?

 

[brs73]

i was under the impression all sub mains needed to be swa.
i never thought t&e was permitted
the cables would be leaving an intake cupboard in a communal area ,they'd be boxed in until they rise up to the ceiling void.i'd say they they need either mechanical or rcd protection.

 

[beaver74]

i was under the impression all sub mains needed to be swa.
i never thought t&e was permitted
the cables would be leaving an intake cupboard in a communal area ,they'd be boxed in until they rise up to the ceiling void.i'd say they they need either mechanical or rcd protection.

did'nt think you could get 25mm T/E

 

[brs73]

neither did i beaver
i've seen it but only in red/black what someone had in their garage and i asked me if i wanted it
handy if you're too tight to buy grommett strip!!

 

[Darkwood]

Treat the 25mm like any cable as in 'you way up the route' if it is prone to damage etc then consider swa, if not i see no reason why not as long as all the cable calcs ok.
Just remember because the earth in a t&e is been used by multiple circuits then you are required to run an additional earth with each t&e to bring the cpc csa equal or greater than the phase conductor.

 

[Spudnik]

25mm split concentric FTW

 

[barx]

I'd probably use split con too.

 

[brs73]

just looked into split con,
i havent used it before
think i'll use that with an rccb protecting the cable
i've tried looking at pics but they're not very clear
is a 16mm earth incorporated inside the cable?

 

[Spudnik]

yes it is.

However you must treat it like T&E with regards to RCD protection etc

 

[ohmeelectrical]

Is the requirement for rcd protection for the cable or protection from fault (direct) contact?. If it is the latter then you could never achieve discrimination with the cu rcds. I have seen posts from cable manus stating that split conc will not comply with the 17th ed, I can only imagine this is the reason.
I copied this statement from Prysmian cables from the Voltimum forum:Subcategory - 4. Standards Relating to Cables - Voltimum UK - Electrical Installation Products and Contracting

"Split Concentric

Previous editions of the Wiring reguations have allowed the use of split concentric cables in concealed walls.

We would however refer you to the current 17th edition of the Wiring Regulations, specifically section 522.6.5 - 522.6.8, with regard to running cables in buildings. It should be noted that split concentric cable does not comply with the requirements of these clauses."

If it is ok then what is the best way to terminate the neutral and earths?

 

[Spudnik]

As i stated before, split concentric must be treated the same as T&E and RCD protection used where required.

 

[mark_the_spark]

I would use a split con cable like barx recommended however id run it either 50mm in the floor joists and protect it with 4mm ss plate if you have to run it in the walls (earthed) as if you put a 30ma RCCB at source protecting it you will not be able to meet 17th requirements with regards to segrating RCD protected circuits.

Hope it helps

Mark

We would however refer you to the current 17th edition of the Wiring Regulations, specifically section 522.6.5 - 522.6.8, with regard to running cables in buildings. It should be noted that split concentric cable does not comply with the requirements of these clauses.

didnt know that....

 

[mazdaman]

Installing an RCD on a sub-main would not comply with 17th regs because if the RCD did trip caused by a lamp blowing etc, the whole flat would loose supply. You need to install 2 RCD's in the flat as per 17th so you only loose part supply. This leaves you little choice but to install SWA which is NOT protected by RCD. You can use split con but it will need to be installed on the surface but again withoout RCD protection.

 

[NoSparks]

I'm sorry but this thread seems to be a storm in a tea cup. The regs are quite clear. 522.6.5 for floors and 522.6.6 for partitions state that cables must be protected against damage by normal use of the building, or by the like of screws and nails. One approach being to bury the cable more than 50mm from the surface, the others to provide mechanical protection. SWA cable (complying with BS5467, BS6346, BS6724, BS7846, BS EN 60702-1 or BS8436) satisfies the requiremets for mechanical protection. (Though personall I find this quite incredable)

So SWA is acceptable without additional protection. All other cables must be protected by one of the methods prescribed in these regs.

Reg 522.6.6 (v) is an escape clause for cables burried in "safe zones" less than 50mm deep and not having mechanical protection. In this case the cable is REQUIRED to be protected by an RCD. (Reg 522.6.7)

The regs do not prohibit the conncetion of two RCDs in series, however reg 531.2.9 provides for discrimination between them. (I assume "slow blow" RCDs are still available).

I cannot find the reg specifying or implying that 2 RCDs must be used , although I recall the text that "due consideratiobn shall be given to the relative loading", maybe somebody can give me the reference.