Routing 16sqmm SWA externally - recommendations?

[Sidewinder]

I was planning on using 3 core in case the sparky needs to use one for earth. Not planning to do the termination myself, just the routing...

The 90deg bend suggestion will work perfectly with the installation I have. Cheers

You don't need an internal cpc (earth core) most times with SWA correctly installed & terminated.

 

[Blue Duck]

Just playing Devil's advocate here...

I asked my local wholesaler what he sells more of 2 core or 3 core SWA and he said they stopped stocking 2 core over 10 years ago as nobody ever asked for it.

opcorn

 

[Simon1013]

Sparky says 3 core so I guess that's the stuff...

 

[Sidewinder]

Just playing Devil's advocate here...

I asked my local wholesaler what he sells more of 2 core or 3 core SWA and he said they stopped stocking 2 core over 10 years ago as nobody ever asked for it.

opcorn

Why devils advocate?

I was told by one guy at a wholesaler that 2 core was illegal!

Twat.

The SWA is a valid cpc & bonding conductor, as long as it is adequately & correctly sized & terminated.

The issues are that there are too many idiots that think the SWA is unsuitable as a cpc, & can't terminate an SWA gland correctly to provide an adequate earth path.

I saved a client £x,000's specifying 2 core 2.5mm SWA over 3 core.

The SWA has to be correctly connected to earth anyway, so why have a 3rd core that is unnecessary?

We did order 10km of the stuff mind!

 

[apprentice87]

Exactly as sidewinder says....

You will have to do the "two level" method to get it round the corners though. The minimum bending radius will be about 5" so like bending it round a basketball... You would have to chisel right through the outer skin of you house brickwork into the cavity... As Tony said, not a smart move..

There are rules as to the clipping of the stuff, but i have not got the book here, [In the OSG i think???]

How long is the run?? what is it for?? earthing type??

john..

 

[Blue Duck]

Spoke to the guy that runs the place, it's a local place for local people and not a big corporation that employs muppets because they are cheap.

Don't think that using the armour as the earth is a problem as long as you can do the calculations to back it up

Was just wondering what is considered the best way as I have always used 3 core, maybe I'm just lazy but I don't do miles of the stuff.

I once read an EICR from a large firm that stated that none of the circuits had a CPC and it was dangerous and put warning stickers all over the fuse box.

He obviously hadn't seen MICC before!

:coat

 

[Rob_the_rich]

Exactly as sidewinder says....

You will have to do the "two level" method to get it round the corners though. The minimum bending radius will be about 5" so like bending it round a basketball... You would have to chisel right through the outer skin of you house brickwork into the cavity... As Tony said, not a smart move..

There are rules as to the clipping of the stuff, but i have not got the book here, [In the OSG i think???]

How long is the run?? what is it for?? earthing type??

john..

bending internal radius is 6x overall diameter of cable for armoured stranded conductors

supports; armoured cable diameter 9<d<=15 horizontal 350mm vertical 450

15<d<=20 h 400 v 550

20<d<=40 h 450 v 600

from osg

 

[Rob_the_rich]

Why devils advocate?

I was told by one guy at a wholesaler that 2 core was illegal!

Twat.

The SWA is a valid cpc & bonding conductor, as long as it is adequately & correctly sized & terminated.

The issues are that there are too many idiots that think the SWA is unsuitable as a cpc, & can't terminate an SWA gland correctly to provide an adequate earth path.

I saved a client £x,000's specifying 2 core 2.5mm SWA over 3 core.

The SWA has to be correctly connected to earth anyway, so why have a 3rd core that is unnecessary?

We did order 10km of the stuff mind!

playing devils advocate here myself. The wording of 521.5.1 does state that the appropriate cpc are contained within the enclosure, and that at the entry, the conductors (including the cpc) are only collectively surrounded by ferromagnetic material, such as the sheath. Seems to suggest that a separate cpc in the cable is required.

 

[Sidewinder]

Radishes Rob, you are now talking ****, so please don't continue.

Look at 543.2.

Reproduced here for you:

543.2 Types of protective conductor

543.2.1 A protective conductor may consist of one or more of the following:

(i) A single-core cable

(ii) A conductor in a cable

(iii) An insulated or bare conductor in a common enclosure with insulated live conductors

(iv) A fixed bare or insulated conductor

(v) A metal covering, for example, the sheath, screen or armouring of a cable

(vi) A metal conduit, metallic cable management system or other enclosure or electrically continuous support system for conductors

(vii) an extraneous-conductive-part complying with Regulation 543.2.6.

 

[Rob_the_rich]

Not saying it can't be used as a cpc, just saying that the regs seem at odds with the practicalities of terminating onto a ferrous enclosure.

Did I mention I was playing devils advocate? My last on this subject.

 

[Sidewinder]

Not saying it can't be used as a cpc, just saying that the regs seem at odds with the practicalities of terminating onto a ferrous enclosure.

Did I mention I was playing devils advocate? My last on this subject.

Rob,

I'm not saying this to draw you back to post, but, that ain't even devils advocate mate sorry.

 

[Phoenix]

Not sure if its the same everywhere, but round here there is a trend to use 3core for SP+N and 4core of TP+N not sure why the very slight change in armour CSA (between 2c and 4c) suddendy chances peoples mind about whether to use it as a CPC.
 Its so mush so that you cant get 2c off shelf.. special order only and by the time you have paid for delivery and lost time waiting for it, you could have saved money by using 3core, its a self fullfilling situation!

The think to watch out though, is on PME if the cpc of a submain is having to be a bonding conductor as well, then SWA is unlikely to be suitable, generally need to provide a copper cpc

 

[Sidewinder]

Not sure if its the same everywhere, but round here there is a trend to use 3core for SP+N and 4core of TP+N not sure why the very slight change in armour CSA (between 2c and 4c) suddendy chances peoples mind about whether to use it as a CPC.
 Its so mush so that you cant get 2c off shelf.. special order only and by the time you have paid for delivery and lost time waiting for it, you could have saved money by using 3core, its a self fullfilling situation!

The think to watch out though, is on PME if the cpc of a submain is having to be a bonding conductor as well, then SWA is unlikely to be suitable, generally need to provide a copper cpc

Not always, have you looked at Johns paper?

 

[Phoenix]

I have read it, it was a few years ago now mind.

If I remember the crux of the matter is that table 54.8 / 54G gives mimimum sizes for bonding conductors in copper, other materials may be used if the size chosen results a *conductance* equal or better to the tabulated size of copper, and the ratio between copper/steel conductance being approx 8.9. So if you take a 100A TPN supply, TNCS with required bonding of 10mm copper. That is 8.9x10 = 89mm of steel required if its to be bonding conductor as well. With XLPE 4 core that means a cable of 50mm² (90mm of steel) or above. While if its a longish run the 100A supply might be in 50mm. *Generally* it would not. So *Generally* need to provide a copper conductor, but not always

Edit:

Thats from memory anyway, feel free to correct if wrong

 

[apprentice87]

Sounds good to me!!

No "topping up" or conductors either mind.. So, if you need, say, 16mm or its "copper equivalent" you cannot have say, a 10mm additional conductor in parallel with the the armour [or any internal core you might use] to make up the 16mm, the 16mm has to be provided in "one shot" as it were. IF you use an internal core as bonding conductor, it also has an effect on the rating of the cable as the bonding conductor is assumed to be carrying "some" current. As to how much current, i would venture that nobody knows!!!! All depends on type of earthing employed and if there are any faulty neutrals in the area i guess!!

john..

 

[Phoenix]

Sounds good to me!!

 As to how much current, i would venture that nobody knows!!!! All depends on type of earthing employed and if there are any faulty neutrals in the area i guess!!

I'm always reminded of the following....

Quote

Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance.

I note that the papers have a story about the Smiler ride at Alton Towers getting stuck again after re-opening recently. I sometimes do wonder about how many unknowns there are in those thing from things such as uneven loading, etc. Well at least this time no one put the lockouts on over ride on the basis of something being where it was supposed to be, without checking that it was! (I seem to remember that was what the cause was found to be?)

EDIT: Can a mod fix my quote please, it seems unwilling to let me so so and I cant even see the tags in edit mode!

 

[apprentice87]

Ha ha!! That sounds about right!!

john...

 

[Adam3]

I am doing some of the legwork for extension wiring (being overseen by an electrician) - sinking boxes, wire runs etc. One of my tasks is to run a length of 16sqmm SWA externally from the main supply to the location of the new consumer unit. Obviously, leaving the ends dangling free for the chap to connect up properly...

There don't seem to be any hard and fast guidelines on routing SWA with regard to clipping, protection etc so I was planning on simply routing it round the outside of my house, just below the DPC, clipped at (say) 200mm intervals using those large cable clips. My sparky did say that I might want to use additional protection, and mentioned some kind of 'U' shaped cover and associated hardware that encloses the cable. Since the cable will run along a wall which is adjacent to a public path, I wouldn't mind the additional protection if only to avoid yobs kicking at the wire and pulling out the clips. I couldn't find any such hardware doing a basic google search....but not sure exactly what it would be called anyway.

Any general recommendations? I feel I am challenging the sparky with enough 'Building Regulations' questions to bother him with this, and anyway, am more interested in general what people do since I figure there must be a number of ways to skin this cat.

Cheers again all

You could add some sort of steel capping if you wanted to. Altough SWA (steel wire armoured) cable is considered by BS7671 to offer adequate mechanical protection against nails and such like.

Still think yobs would havw some diffculty damaging it by kicking it unless they get a hack saw too it.

If uour still worried about them pulling it off couuld you place it out of reach?

The cable clips you will need are called cleats. Be sure to get ones to suit size of cable

 

[leesparkykent]

I've had the argument loads of times about using the armour as combined CPC and bonding conductor.....Its clearly stated within the regs that it has to offer equivalent conductance of copper if other metals are used i.e the steel armour when used as a bonding conductor. 16mm 2 core hasn't got a hope in hell......Bit of a silly suggestion IMO!

 

[apprentice87]

How is using 16mm 2 core a silly suggestion???

Who said that the armour is going to be used as a bonding conductor anyway?? Might be going to TT the shed or whatever it is

john..