newbie in training !!!!!!

[wa209]

Hi all, am doing some evening courses on electrics and have passed my 17th, 2392 and the Part P. Now onto some more !!1
Love reading these forums for bits and pieces , but have become a bit confused re SWA.
I have read about using the third core of 3 core swa as the earth if say connecting straight into a cu , but also i have read where we also put an earth onto the sheath ?Can someone help me out with this ?

 

[chivers67]

Depends on the size of the SWA, I'll let you find out what size conductors you can use the outer core for an earth

 

[OwainDIYer]

The armour must always be earthed, usually at the supply end.

If the armour is not large enough csa to use as the earth conductor, one of the cores must be used as earth.

If the cable is running between different equipotential bonding zones then the armour must be insulated, usually at the load end, to avoid exporting the earth. This often applies to PME installations to outbuildings, caravans etc.

EDIT: armour is the metal wire. Sheath is the outer insulating cover.

 

[PrenticeBoyofDerry]

Love reading these forums for bits and pieces , but have become a bit confused re SWA.
I have read about using the third core of 3 core swa as the earth if say connecting straight into a cu , but also i have read where we also put an earth onto the sheath ?Can someone help me out with this ?

the third core can be used as a CPC must be sleeved accordingly though also the armour can be connected to earth terminals at both supply and feed ends.

 

[ricicle]

.... have passed my..... Part P.

Is Part P an electrical qualification then ?

 

[wa209]

Hi , thnaks for replies... no pt p is not an elec qualification..i decided to do it as well as i have no expirience in building regs ( not in my day job at all !!!) so i thought it would be a good idea to have a bit of an understanding. Anyway thanks for your help re my question ?!?!
Thanks for those who tried to help me understand a bit better...slowly but surely the mists lift !!!
Lots more q's to come i have no doubt!!!

 

[holmslaw]

..

 

[ban-all-sheds]

I have read about using the third core of 3 core swa as the earth if say connecting straight into a cu , but also i have read where we also put an earth onto the sheath ?Can someone help me out with this ?

So you've got a City & Guilds qualification which says you know about Inspection and Testing.

You have a City & Guilds qualification which says you understand the Wiring Regulations.

But in reality you don't actually understand about earthing the armour of armoured cable?

It's hard not to conclude that not only has the system failed you by letting you pass these exams, but maybe you are also failing the system by persisting with the belief that you are cut out to be an electrician.

 

[Lanesra]

I have read about using the third core of 3 core swa as the earth if say connecting straight into a cu , but also i have read where we also put an earth onto the sheath ?Can someone help me out with this ?

So you've got a City & Guilds qualification which says you know about Inspection and Testing.

You have a City & Guilds qualification which says you understand the Wiring Regulations.

But in reality you don't actually understand about earthing the armour of armoured cable?

It's hard not to conclude that not only has the system failed you by letting you pass these exams, but maybe you are also failing the system by persisting with the belief that you are cut out to be an electrician.

Sadly the above is true, when I did my 2330 lvl 3 practical exams the 2392 boards where in the same room and they consisted of a cu with a ring (two sockets), a radial circuit (one socket), a two way light circuit and a cooker circuit

 

[wa209]

Wow..... I obviously got the whole wrong end of the stick here. It seems don't ask any questions or you'll be ripped to pieces. You are expected to know everything in advance.
As for wanting perhaps to learn new skills...that's to be frowned on as well.
I can only apologise for wasting the last two post replies time.
But then seeing how many posts they have...i suspect that this is how they spend thier time.
I don't think i've encountered such vitriol and bile before. But then if that's what gets the two of you excited so be it...
How the winter evenings must fly by at your place. Good luck to those who follow..

 

[Spark123]

Good old SWA!! I can understand where you are coming from with the confusion. The armour must always be earthed at source regardless of wether or not you have an additional earth via a core.
It is in essence a lazy way to just use a core as an earth but a lot of people do it as a matter of course.
It all boils down to is the armour adequate as the circuit's CPC or not. You can look at charts such as here: //www.diynot.com/wiki/electrics:earthing_supply_types_and_bonding:swa_earthing which gives you an idea if it complies with table 54.7 however, even if it doesn't you will probably find that the armour on it's own will provide an adequate CPC if you apply the adiabatic equation (regulation 543.1.3), similarly why the reduced CPC of 1.5mm in 2.5mm twin and earth complies.
In a nutshell, it is easier to apply table 54.7 (which is where the doubling up of the CPC comes from) but if you an be bothered to work out the maths then you can save some money by doing the adiabatic equation and selecting a cable without an additional conductor
If you were laying a simple single phase addition such as a 2.5mm SWA to a socket it isn't going to make much of a difference.
If you were laying 1km of 3phase, neutral and earth 300mm SWA then you may choose to do the maths though as 5c SWA is going to cost you a fortune!! (albeit 4c 300mm isn't that cheap to start with!!)