Pros...cons...preferences..

[Baddegg]

after my rather vague thread Friday about finding the 30 mtrs of 10mm 2 core swa In the back of me van.....after some views on earthing to the shed, 3 options as far as I’m aware are
1. Run a single 10mm from main met upto the shed and use that
2. Use the armour of the swa, adiabatic permitting..
3. Connect the swa to the main met at source end and TT the shed
Each option is appruthe same cost wise and it’s my own house so Labour is not a big issue, as per title just after others views and preferences....

 

[Wilko]

Hi - just FYI, from GN8 I read that 2 core swa 10mm has actual steel of 26mm (table B2). Since you only need 22mm (ish) steel to equal 10mm Cu (for thermal effects for 70C cable) then it’s fine.
Not sure, but your 41mm figure could be from 4 core 10mm cable?

 

[Deleted member 26818]

Hi - just FYI, from GN8 I read that 2 core swa 10mm has actual steel of 26mm (table B2). Since you only need 22mm (ish) steel to equal 10mm Cu (for thermal effects for 70C cable) then it’s fine.
Not sure, but your 41mm figure could be from 4 core 10mm cable?

There are 3 different types of SWA cable.
70 degree C PVC 2 core 10mm2 BS6346 SWA has a CSA of 40mm2, and a value for K of 51.
90 degree C PVC 2 core 10mm2 BS5467 SWA has a CSA of 26mm2 and a value for K of 46.
90 degree C XLPE 2 core 10mm2 BS6724 SWA has a CSA of 26mm2 and a value for K 46.

 

[Deleted member 26818]

When calculating the CSA of a protective conductor, using tabulated values, you use the tabulated values.
If you were calculating using manufacture’s data, you would use their values.

 

[Wilko]

There are 3 different types of SWA cable.
70 degree C PVC 2 core 10mm2 BS6346 SWA has a CSA of 40mm2, and a value for K of 51.
90 degree C PVC 2 core 10mm2 BS5467 SWA has a CSA of 26mm2 and a value for K of 46.
90 degree C XLPE 2 core 10mm2 BS6724 SWA has a CSA of 26mm2 and a value for K 46.

Hi - so are you saying that GN8 is wrong or that I’ve read it wrong? .

 

[andyb]

Am I missing something here?
If you know that the cpc is 26mm, why do you need to do the adiabatic?
Apologies if I'm being stupid.

 

[Pretty Mouth]

Baddegg, genuine question - why use Cmin when calculating the fault current for adiabatic? Would this not give a best-case scenario lower fault current, where we would want a worst-case high fault current?

 

[Baddegg]

Good question pretty mouth, havnt used the adiabatic in real life scenario before so just went through my notes, this was a good opportunity to do some calcs and get the brain working agian as it’s my own property, I will be redoing it all this evening but as Andy points out it’s all a bit academic as we nlkniw the csa anyway.......possibly maybe

 

[Charlie_]

The nicknames/profile names on this forum, are you boys also know as this in the real world?

Would feel a bit uneasy shouting over to pretty mouth on a building site

 

[Wilko]

Hi - no questions can be stupid .

My thought is - the actual steel in 2x10mm swa is at least 26mm which when converted with the appropriate temperature rise k factors is equivalent to more than 10mm copper so it’s going to be ok for CPC. As you say, no real need to look at the adiabatic equation for that circuit.

Happy to have feedback if I’ve got this wrong .

 

[Edtwozeronine]

You think the cable is amusing....I’m off to do the adiabatic! Wait till I post them maths up ha ha ha

Isn't the adiabatic shore somewhere near Albania?

 

[Deleted member 26818]

Hi - so are you saying that GN8 is wrong or that I’ve read it wrong? .

Don’t know what GN8 says.
I just go by the sizes for the British Standards and the values for K in BS7671.

 

[Deleted member 26818]

Am I missing something here?
If you know that the cpc is 26mm, why do you need to do the adiabatic?
Apologies if I'm being stupid.

If the CSA of the Steel Wire is 26mm2.
It’s not a given that the copper equivalence will be sufficient.

Here’s a link to a chart produced by John Peckham, for at a glance checking the CSA of the Steel Wire is sufficient:
Use SWA as CPC, a guide to the acceptability of steel wire armour use as CPC. - https://gadsolutions.biz/regulations/swa-as-the-cpc

Sure this has been posted in the past.

 

[Pretty Mouth]

Baddegg, my experience of the adiabatic is limited too, hence the question. Just about getting my head around it now though, i think.

Charlie, the name Pretty Mouth comes from the movie Deliverance (my favourite romantic comedy), what makes you so sure I'm a boy? Haha

 

[Deleted member 26818]

Must admit, I hadn’t noticed that he Baddegg used Cmin in his calculation.

 

[Charlie_]

All this talk of Cmin and pretty mouth is getting too much for me