Supply to Consumer Unit via 10mm SWA!! What to replace with?

[mattg1985]

Hi, im new to the board.

I live in a 1st floor flat and my consumer unit is in my hallway. The meter and isolator are located on the ground floor in a utility room. It is a 106 year old building converted to flats and im guessing the installation is 30+ years old.

Currently the supply from the meter to my consumer unit is via 12m of 2 core 10mm steel wired armour cable feeding a re-wirable wylex board. The cable goes up through the utility room roof (which is below the stairs), clipped to the communal staircase wall and disappears through the wall into my floor space where it reappears and goes up the wall to my CU.

I am re-wiring the entire flat and will be fitting a 17th edition board. Im up to date with 17th edition and have 2391 but just not with a trade organization (hope to use this for entry).

What should i use for the 'tails' as it were? Is SWA acceptable between the meter and CU and at that length? I haven't come across an instalation like this before so would apprieciate some advice.

Thanks for you time!

Matt

 

[RF Lighting]

At the meter end, is there a switchfuse between the meter and the SWA?

 

[mattg1985]

Yes there is a 60A switch/fuse.

The SWA looks like 10mm but not 100% sure. It may be 16mm but doesn't appear to be that big!

 

[ColJack]

do you need a switchfuse?
I mean of course as it's 10mm and the main fuse isn't going to be small enough to protect it, but if he replaces it with 25mm or something capable of taking the FLC of the main fuse, it's protected isn't it?

 

[RF Lighting]

Assuming there are no derating factors to take into account, and it is clipped direct, 10.0mm² 2 core SWA is good for 67A

 

[RF Lighting]

do you need a switchfuse?
I mean of course as it's 10mm and the main fuse isn't going to be small enough to protect it, but if he replaces it with 25mm or something capable of taking the FLC of the main fuse, it's protected isn't it?

You need your own fuse to protect your installation. You must not rely on the suppliers fuse for this.

 

[mattg1985]

I would uprate the switch/fuse to match the current carrying capacity of the cable and main fuse in consumer unit. Therefore protecting the cable and potential fire risks.

It may well be 16mm at the moment but as i have nothing to compare it with at hand i can't really be sure!

What would be the best bet for replacement of the supply cable?

Three core 25mm SWA so i can use the third core as an earth or just two core and use the protective conductor for earth. I assume the 25mm rule still applies to this situation?

Ant recommendation where i can get 25mm SWA cable from? Don't seem to have it in my electrical suppliers... lol

 

[mattg1985]

I also need to replace tails between meter and switch fuse as they are not double insulated and also there are two different lots of cable connected with a terminal block and wrapped in insulation tape!!

Looking at it now, the tails downstairs supplying switch fuse are 16mm and my SWA cores are definately 10mm!

 

[ColJack]

do you need a switchfuse?
I mean of course as it's 10mm and the main fuse isn't going to be small enough to protect it, but if he replaces it with 25mm or something capable of taking the FLC of the main fuse, it's protected isn't it?

You need your own fuse to protect your installation. You must not rely on the suppliers fuse for this.

fair enough, specifically which reg, and what about the 25mm DI from cutout to meter to board? what protects that then?

 

[RF Lighting]

I don't know if it's the same everywhere, but many DNO's will only allow tails to be connected directly to their supply, and they are limited to a maximum of three meters.

 

[oharaf]

Interesting one this one. Looked at a similar job in Harrogate a couple of months back.

I intended to uprate the switch fuse 2 100A and use 25mm 2 core SWA.

SWA came in at around £250. As the owner had no idea of what he really intended to put in I treated it as a house, 25mm supply, 16mm MEB and 10mm Services bonding.

 

[ColJack]

I don't know if it's the same everywhere, but many DNO's will only allow tails to be connected directly to their supply, and they are limited to a maximum of three meters.

that would be the same regs that securespark and I are / were discussing on the "calling all sparks" thread... 432, 433 and 434 off the top of my head... ( Position, and omission of devices for protection against overload, and position of devices for protection against fault current.. )

 

[mattg1985]

It looks like i will have to use three core 25mm SWA then unless i can use the armour as the earth like is currently being done? I am guessing that this is not satisfactory?

Is there any issue with the third core being used for the earth or does it need to be run seperately?

 

[ColJack]

that would depend on the results of the adiabatic equation you'd need to do..

you could always use split-con..

as for the inevitable question "what's split-con".. it's similar to SWA, but there is only 1 central core which is the live, and it's surrounded with strands which are the neutral and sometimes also earth.

 

[mattg1985]

Thanks for the reply, i will look into split con.

Just curious as to what you mean by the adiabatic equation in terms of the supply as thats what i used to do in my thermodynamic lessons at college... but that was relating to fluids.

Unless you mean current carrying capacity of the cable through the environment its running?