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Swa Csa


jimmybobbob

Question

Hi,

 

can anyone point me in the right direction where I can find the tabulated value of the csa of a swa cable in the new regs (yellow). Also do I then need to carry out a calculation to find out its actual csa as a copper csa equivalent

 

many thanks

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22 answers to this question

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Table 4D4A onwards will tell you all you need to know.

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Ok,..got that bit, im filling in an installation cert and need to record the csa of the supply swa that has been installed by another contractor to a sub board?!

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I'm confused with the question....

I'm guessing he means the copper equivalent csa of the armour sheath.... However?????

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should I say that the sheath is acting as the cpc..my bad

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Just put the live conductor size and then put SWA as the earthing conductor size, you'll be fine, as long as it complies.

There is a table in GN1 though.

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I "think" what you mean it this. You want to know the CSA of the armour of this SWA you are on about...

 

Well....

 

If you are using it as the CPC then all you need to know is the R2 for the armour [and R1 for the conductor] so you can work out R1 + R2 for the cable as a whole.

 

Now, you ask about "copper equivalent" for the armour. This leads me to think that the armour is being used as a bonding conductor. If it is, then yes, you will need to know the copper equivalent, if not, then you do not need to know this.

 

Anyway, this might help: http://staffing-systems.co.uk/index.php/SWA,_armour_equivalent_copper

 

john..

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.....when you say as long as it complies...this is where I could do with the relevant information to help (ie. csa of the sheath and the relative resistance of the steel to copper) if that all makes sense. Unfortunately I only have 7671,onsite guide and GN3


Ok here it is......

 

Another contractor has installed a 3P&N DB

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Hi Jimmybobbob,

 

Remember, you will only need to check the copper equivalent if the armour is being used as a main equipotential bonding conductor, If it is just being used as a CPC then no need. Hope the table was ok, i can usually find the much better Wiley ones, but they are not loading properly today!!

 

john..

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Ok here it is......


 


Another contractor has installed a 3P&N DB using 4 core 25mm SWA fused down via an MCCB is the switch room rated at 100Amps. They have utilised the SWA sheath as the cpc to the new DB.


 


My side,


 


I've installed 7 twin sockets and 1 wall heater via a ring main on a 32amp 30mA RCBO &  4 x 600 by 600 CAT2 fittings in a grid ceiling on a 6amp MCB.


 


Just doing the test cert....


Earthing conductor Material: SWA


Earthing conductor CSA: ???????


 


I used to have noted down amongst endless paper work where there was a table.... 


 


any help happily taken

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.....when you say as long as it complies...this is where I could do with the relevant information to help (ie. csa of the sheath and the relative resistance of the steel to copper) if that all makes sense. Unfortunately I only have 7671,onsite guide and GN3

Ok here it is......

 

Another contractor has installed a 3P&N DB

 

That's a little confusing, but never mind, just get the data on the sub-main cable from their certification for it, then you have the actual data on what has been installed.

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Would this not class as the main protective conductor for that particular DB as its remote to the main incomer?


Sorry sidewinder (hit the enter button to early...driving me mad trying to find an answer all day)

 

Ive done and gone....Im not to sure if the other contractors are on site (no sign of test certs)

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Hi Jimmybobbob.

 

No, as all extraneous conductive parts [say like the building frame, or steel gas or water pipes] will, or should have been, bonded to the MET, so all your cable armour is doing is acting as CPC for the new board, so just enter: Material; SWA. CSA; SWA, as Sidewinder says.

 

Now, if your cable was feeding a SEPARATE installation, say like an outbuilding, THEN the armour could well be used as a bonding conductor linking any extraneous parts of the new installation back to the MET...

 

Oh, and the answer for the CSA or the 4 core 25mm cable armour is 70mm with a copper equivalent if you need it of 22.5mm

 

john..

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Hi John,

 

Ok I guess that is my answer... whilst on the topic, a couple of things if you please.

 

Where would I find such an answer of 70mm?

 

Also if the cable were to supply an external building exporting PME, then would the SWA would be suitable as its greater than 16mm......but then i guess this is where the copper equivalent would have to be calculated, right?

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Yes.... and no!!!!

 

First off, yes you understand exactly what i meant and why you would need to bother with such things when you say;

 

"Also if the cable were to supply an external building exporting PME, then would the SWA would be suitable as its greater than 16mm......but then i guess this is where the copper equivalent would have to be calculated, right?"

 

BUT, in the scenario you describe, the CSA required for the bonding conductor cannot always just be taken as "16mm"

 

You see, the CSA required would be related to the size of the NEUTRAL conductor in the service cable to the ORIGINAL installation. So if the main building had a wacking great big supply, you might well have to run one very big bonding conductor to the second building, REGARDLESS of how small the CSA of the submain was..

 

The link i gave in post 8 gives you the chart you need which is where i got the info from!!

 

john

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Mmmm,

One small problem arises with exporting PME,

you need to obtain the DNOs permission,

Do you think it's likely they will grant it,? 

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ok and further more to that....i guess the size of the seperate earth would have to be installed from a fault current calculation of the tripping current of the protective device and installation methods used right?


does it say anywhere in the regs that you cannot export PME? After all...which will be a better earth, a TT on a poxy rod or PME....

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Don't fit poxy rods?

Use proper ones? ;)

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:slap do it once, do it right...it is what it is

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It's not a reg,

It's a condition of supply from the DNO, it's their earth.

Oh, a TT that you have control over will always be better than something you have NO control over. 

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could you imagine the cost and paperwork involved to put a supply into Mr Jones' shed down the way so he can see the rest of his day's through listening to his DAB building his model aircraft.....MAYBE, just maybe he should have some PV panels put in.

 

If you loose PME coming into any premises full stop.....big problems (very unlikely but never say never)

 

Appreciated though having control of what we install is the better option

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What's the problem,?

If you have PME simply don't export the earth,

TT it, simple, no hassle, job done.

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