Can we use the armour of an SWA as the CPC???

[Dave_]

ah sorry! im talking about using armour as an earthing conductor... not a bonding conductor.... and not specifically PME, where larger bonding conductors are required due to the nature of the earthing arrangements......

ha ha different wavelengths....

 

[joshjoynes1988]

Hi all,

Just wondering if any has/knows where i can get a table for aluminium armoured cable earthing like the SWA ones?

Cheers Josh

 

[IQ Electrical]

I'm not sure if there's a table but there's a conversion factor, if nobody else posts it, I'll do it tonight when I get back to the office.

 

[Dave_]

hi josh,

if you go on to AEI cables website

you will find the information there

you have to open an account.... just a sign in thing, not a proper trade account

then all the info you want is specific to the product you select

the datasheets being the technical info, showing resistances etc....

or p166 O.S.G has a little info on it

 

[Rochelle]

I have seen numerous times what happens to the armour when the sheath of the cable is damaged, and water starts to ingress.

 

[malcolmsanford]

I have seen numerous times what happens to the armour when the sheath of the cable is damaged, and water starts to ingress.

Yes the same as I have seen damage on conduit, trunking. T+E , etc I think any cable/containment damage will adversly affect the reliability of the chosen method.

 

[smartspark]

I use both sometimes, if its outside and posible that it can be hit or perish I use the armour as a secondary defence at the sub main board and the third core cpc between the main dis board in the house and the sub main.

 

[TAFF4]

The ratio for electrical conductivity between copper and steel is about 8 or 9:1, depending on the make up of the materials.
The chart you are refering to probablly relates to the thermal resistivity.

So, do we divide the tabulated figures in the 'earthing nuts' chart by the 8.8 resistivity factor of copper against steel or not ?

Are these figures purely a csa equivalent and not a resistivity comparison.

Dave's project example will not be correct, if that is the case.

Help !!

 

[TAFF4]

This looks like the answer ?http://www.------.org/forums/forum/...d=23890&STARTPAGE=1&FTVAR_FORUMVIEWTMP=Linear

Choose say 25 mm2 Cu and see that it has a resistance of 0.727 Ohms/Km

Look at the steel csa for say 4 c 25 mm2 and get 70 mm2 and this has 2.3 Ohm/Km.

Divide 0.727 by the 2.3 to give 0.316

Multiply the copper 25 mm2 by this 0.316 to get the copper equivalent of 70 mm2 steel ie 7.9 mm2.

Divide the original 70 mm2 of steel by 7.9 to get a figure of 8.86.

 

[Deleted member 26818]

It would depend on what it is you wish to achive.
If for instance you wish to determine whether the armour of an SWA cable is suficient to be used as a CPC, then I would either use the cable manufacturer's data or perhaps a chart that you feel is reliable, and then apply the adiabatic equation.
If however you wished to determine, whether the armour was suitable to be used as a bonding conductor, I probablly wouldn't bother making the attempt other than as an exercise to prove to someone that the armour is not sufficient.

 

[TAFF4]

Hello again sparkies, here is a snippet of my project submitted for 2391-20 qualification regarding minimum size of S= √(1966²×0.1)/46=13.5mm²

Using the table provided by AEI I can see that a 70mm² four core cable has a 131mm² armour CSA, therefore this is perfectly acceptable.
[/I]

This shows that the armouring can handle 10x the amount of fault current that is required....!! no need for seperate CPC ;-)

Please note: values for armour and conductor resistance are from AEI cables, vvv useful!!! as you dont find them in the regs book, OSG etc. (OSG up to 50mm and doesnt show armour resistance.... there is a way of calculating conductor resistance but i cant remember how.....

Was going to post link to AEI site but you need to be a member to view the datasheets.... if anyone wants to see them and needs assistance then let me know

hope this helps AMP DAVID!!!

The AEI table suggest that the 'effective csa of armouring' is 16.38 sq.mm. Which seems closer to the mark and still good enough but not 10 times as good.

I am not criticising the findings but trying to get this to sink into my bald/grey head and have found this thread very useful.

Thank You.

 

[TAFF4]

It would depend on what it is you wish to achive.
If for instance you wish to determine whether the armour of an SWA cable is suficient to be used as a CPC, then I would either use the cable manufacturer's data or perhaps a chart that you feel is reliable, and then apply the adiabatic equation.
If however you wished to determine, whether the armour was suitable to be used as a bonding conductor, I probablly wouldn't bother making the attempt other than as an exercise to prove to someone that the armour is not sufficient.

Got it now.Thanks.

 

[madmac]

Just throwing this in because i'm sick of reading these threads about very basic electrical practise. If you have to ask questions like this then you shouldn't be touching any electrical installation above a 13amp plug!!!

 

[IQ Electrical]

Just throwing this in because i'm sick of reading these threads about very basic electrical practise. If you have to ask questions like this then you shouldn't be touching any electrical installation above a 13amp plug!!!

I don't agree at all, this has been a good thread, especially the points relating to the adiabatic and copper-steel conductivity ratios.

 

[tonys]

Shocking really