Cable size

[uksparks]

Hi,

I am going to be connecting an out door power supply, away from the building, its all metal casing.

The supply is 10mm, I am using a 3 core SWA for part of the run, the inside part was going to be in twin and earth, but then I was just thinking, going on table 54.8 section 544.1, am I looking into this too much or does it need to have a 10mm earth as its extraneous metal which is fixed into the ground?

In which case I was just thinking of running 3x 10mm inside the building so the earth is 10mm too to them comply with min size of bonding conductor.

I am right to make it 10mm throughout the entire run aren't i?

 

[telectrix]

what's the earthing system?

 

[uksparks]

Pme / tncs

 

[telectrix]

are you saying that the outbuilding is metal construction? if so, earth the SWA armour at house end but then TT the outbuilding.

 

[uksparks]

No its not a building, its a free standing post on a metal ground mount kit bolted into a concrete pad in the ground, all metal.

Its a commercial property / warehouse.

 

[uksparks]

I was just going to go with make it 10mm all the way because its done then.

 

[uksparks]

I could strap a 10mm earth along side the twin and earth, or alternatively just use 10mm SY.

 

[spark 68]

Your Bonding size in that case depends on the size of the incoming Neutral, not necessarily the tails size, depending on type/location, length of run and where the remote part is situated, a remote TT might be a consideration to take into account

Edit: beaten by Tel

 

[telectrix]

hmm. new one to me. let's see what other minds think. the 10mm sounds like a way forward.

 

[uksparks]

its a three phase incommer with 25mm from each and the neutral is 25mm.

I think ill just run some SY inside as thats all 10mm then, I wonder if that will leave me a problem crimping the SY to the SWA...

 

[uksparks]

I was just going to use an adaptable box to make the joint as cannot get the SWA through the wall without looking a mess, so need to joint it inside.

 

[uksparks]

I have just realised I have quoted for 10mm and it was meant to be 16mm, DAMN!!

 

[davesparks]

Why not just run SWA all of the way? There's no sense putting a joint in a brand new cable if it can be avoided.

And as for SY, i'd say it's probably not the best choice. Unless this circuit needs electromagnetic shielding, but then SWA won't be any good if it does.

 

[uksparks]

Its not possible to get it through the wall without looking a mess, unfortunately its not possible.

 

[davesparks]

So what made you select SY for this job? Why does it need an electromagnetically screened flexible cable designed for control circuits and according to manufacturers data sheets should not be connected to the public electricity supply?

 

[uksparks]

Well it was really just an easier way of getting 3x 10mm in one cable, but am just thinking of alternatives now as the run needs to be 16mm, not 10mm, thats my fault, I was basing it on the original loading.

So will rin 16mm SWA to adaptable box, then from there to the dist board I am not sure yet.

 

[uksparks]

So what made you select SY for this job? Why does it need an electromagnetically screened flexible cable designed for control circuits and according to manufacturers data sheets should not be connected to the public electricity supply?

What would your preference to running 16mm line and neutral and a 10mm earth for 9 meters in some basket be then?

 

[davesparks]

What would your preference to running 16mm line and neutral and a 10mm earth for 9 meters in some basket be then?

16mm 3core SWA

 

[uksparks]

16mm 3core SWA

Normally that would be my choice too, but its just not really possible, ill just for 16mm twin and a 6mm earth, thinking about it, it doesn't need bonding anyway as its outside the equipotential zone. Im just being thick. it needs earthing, but not bonding.

Ill just work out the fault current and see, but im sure 6mm will be fine.

 

[davesparks]

Why is it not possible to run SWA but is possible to run SY or T&E?