adiabatic and what to do

[17thman]

I have the opportunity of installing the wiring for shower, extractor, isolator and fused spur for elv waste pump in 60 flats ( retirement home). I have looked at some of the cu's and note that they are all full rcbo protected and have mains supply tails of 10mm2 copper. The main earth is 10mm copper glanded to what i thing is steel wired armoured cable ( all plasterd in. The main fuses range from 60 to 100A bs1361 type II.

Now if i use the 100A and the adiabatic. 904 x 904 x 1.3 square rooted, divided by 93(swa) that equals, 11mm2. How can i work out if the steel wired armour is adequate for the job, or am i buggered.

They were all periodically tested last year.

Thanks

 

[ColJack]

where'd you get the 93 from?
that's the K for aluminium armour
K for steel armour is 51..

where'd you get the 904 from? and why 1.3?

once you have the required equivalent size of the SWA then it's just a case of measuring the CSA of one strand and multiplying by the number of strands..

 

[17thman]

Hi Coljack,

The 93. was from the second table table. I looked at it again then realised that it was the third table i should of looked at. Either way I , the result is greater than the 11 or 20. There is a short lenght of 10mm glanded to the swa, the box is all plastered in behind the cu. the supply side is behind locked babinets, i pressume it is swa. I cannot measure a strand.

The 904A is the mefc and the 1.3 is from difig 3.1 from time curent.

Thanks

 

[securespark]

Sure it's SWA and not split-concentric?

EDIT, you've mentioned glands, so I think the answer is yes...

 

[GaryMo]

THIS might be helpful for you. It was written when the 16th Edition was still in play by mostly still relevant.

 

[BSBS]

This also may be usefull www.earthingnuts.co.uk/pdf/pvc_xlpe.pdf

 

[ban-all-sheds]

And of course our very own Wiki.... //www.diynot.com/wiki/electrics:swa-earthing

 

[LoveRocket]

And of course our very own Wiki.... //www.diynot.com/wiki/electrics:swa-earthing

So, the SWA in 10mm^2 two core 90c XPLE does not meet the requirements for a protective conductor. So, an external protective conductor could be ran alongside it, but some reg says that "blah blah blah an earthed metallic covering that meets the requirements for a protective conductor..."

So does this mean that 10mil 2c XPLE SWA cannot be used anywhere that SWA is required?

 

[BSBS]

And of course our very own Wiki.... //www.diynot.com/wiki/electrics:swa-earthing

So, the SWA in 10mm^2 two core 90c XPLE does not meet the requirements for a protective conductor. So, an external protective conductor could be ran alongside it, but some reg says that "blah blah blah an earthed metallic covering that meets the requirements for a protective conductor..."

So does this mean that 10mil 2c XPLE SWA cannot be used anywhere that SWA is required?

It will still offer Mechanical protection and the amouring will still need to be earthed you just cant use it as the circuit CPC. Either install 3 Core or a seperate earth cable.

 

[holmslaw]

..

 

[flameport]

So, the SWA in 10mm^2 two core 90c XPLE does not meet the requirements for a protective conductor.

An important item missing from the table in the wiki is that those values only apply when the XLPE cable is at an operating temperature of 90C.
It is highly unlikely that this would be the case in a domestic situation, as this would require that the cable was operated at full load for an extended period of time. It would also require that the ends of the cable were terminated into enclosures suitable for 90C, which excludes a substantial majority of equipment.

For domestic situations, in virtually all cases, the SWA armour can and should be used as the CPC. A 3rd core or a separate external CPC is not required.

This also means that for most installations to sheds, garages and the like, 2 core SWA is the most suitable cable.

 

[ricicle]

The main concern with SWA is the use of the armouring is not as the cpc but as a main bonding conductor when the cable is used as sub-mains.
Without an additional conductor (internal or external) to use two core SWA as a sub-main in PME conditions can require a pretty hefty cable. The problem being the ratio of resistance between steel and copper.

Off the top of my head I think it's 95mm² two core armour has the same conductance as 10mm² Cu.

 

[Spark123]

And of course our very own Wiki.... //www.diynot.com/wiki/electrics:swa-earthing

So, the SWA in 10mm^2 two core 90c XPLE does not meet the requirements for a protective conductor. So, an external protective conductor could be ran alongside it, but some reg says that "blah blah blah an earthed metallic covering that meets the requirements for a protective conductor..."

So does this mean that 10mil 2c XPLE SWA cannot be used anywhere that SWA is required?

It will still offer Mechanical protection and the amouring will still need to be earthed you just cant use it as the circuit CPC. Either install 3 Core or a seperate earth cable.

The tables tend to err on the side of caution, the adiabatic equation will allow a smaller minimum conductor size to be used.

 

[Spark123]

So, the SWA in 10mm^2 two core 90c XPLE does not meet the requirements for a protective conductor.

An important item missing from the table in the wiki is that those values only apply when the XLPE cable is at an operating temperature of 90C.
It is highly unlikely that this would be the case in a domestic situation, as this would require that the cable was operated at full load for an extended period of time. It would also require that the ends of the cable were terminated into enclosures suitable for 90C, which excludes a substantial majority of equipment.

You can't really state what the operating temperature of the cable is hence the worst case scenario kicks in. A 90C cable may be run at a lower temperature such as 70C and those values used, however the cable needs to be derated to such a value that it doesn't exceed 70C in use.

 

[LoveRocket]

What I'm getting at is that if the SWA does not meet the requirements of a CPC, then the SWA cable no longer complies with the reg that says "earthed metallic covering suitable for use as a CPC", and thus, that type of SWA cable is useless. Even if you use a core or an external CPC, the metallic covering still ain't suitable for use as a CPC.

Seems daft.