I see it a lot where the SWA isn’t serving as a protective conductor which I know it must still be earthed at one end due to being an exposed conductive part. My question is if multiple SWAs are all earthed at the supply end and meet again at a bit of equipment if we then connect all the SWAs together locally is this still classed as earthing even though they are already earthed at the supply? 
Now we are really getting into trouble! An exposed conductive part is (BS7671): Conductive part of equipment which can be touched, which is normally not live but could become so under fault conditions.
Now the sheath plastic is not conductive, so it fails this test, whether it is "adequate" insulation for 230V (which it is). Now consider metal plumbing which is bonded to the installation MET. Is this an exposed conductive part? No because it is not part of the Electrical installation, although it is connected. SWA is not considered an Exposed Conductive Part.
Now the actual question, which is slightly confused. Are you asking if the SWA armour is an Earthing conductor under your conditions, then yes. If it is only connected one end then No. Even if you put an Earth G/Y cable alongside an SWA, the armour can still act as an Earthing conductor too, the current will share all the parallel conductors depending on the resistance of each.
It is not a requirement that Earth or CPC conductors are sheathed, although they should be marked at the ends if not. The SWA sheath PVC is exactly the same as wire insulation, although it may be thicker, but it is only there to prevent corrosion of the wires. Look at trunking and conduit. As much SWA is 90 degree XLPE the same applies, the sheath is insulating. Whilst on that point, sometimes Insulated and sheathed cables get the name "double insulated" Whilst this is true, the sheath is classed as mechanical protection, because it could be damaged and the double cannot be guaranteed. The same goes for SWA but even if exposed the armour is not dangerous under any normal conditions and the likelihood of contact (buried for example) is effectively zero.
The armouring of any S.W.A. cable can't be an exposed-conductive-part cos it ain't exposed to touch.
I feel the the wording of the definition sometimes isn't always helpful. If a part can be made hazardous live by a fault, can't be directly touched because of something around it, but that something doesn't provide sufficient insulation to make the situation safe, then it seems to me there is a problem. Cable sheaths are generally not considered to be adequate for insulation. It's a similar situation with flush steel back boxes surrounded by plasterwork (and 'live wall' consequences). I suppose you could consider the SWA and plastic sheath, or back box and plasterwork, together as one exposed-conductive-part to fit the definition, but that's hardly intuitively obvious.
- Andy.
I am just posting at the bottom of the list of replies.
The armouring of any S.W.A. cable can't be an exposed-conductive-part cos it ain't exposed to touch. It is covered with insulation. But it definitely does need to be properly glanded and earthed at it's origin. (And at its load end as well in most cases).
Also, the S.W.A. is not an extraneous-conductive-part as it forms part of the electrical installation. (See definitions)
I would say that the conductive steel wire armouring is more accurately described as a circuit protective conductor. I often use it with two core cable as such.
Z.
I presume you are not proposing that the armour may sometimes be left totally unearthed.
Therefore when earthed it acts as a CPC for the internal circuit in case of, for example, striking by a spade.
How can it be an extraneous-conductive-part? Extraneous-c-ps are not earthed.
Even if it were, it would then have to be bonded which would have the same result as an earth - not the purpose of bonding.
Mr.Jack would be more correct in his thinking of it as an exposed-c-p which has to be earthed so we are back to square one - earthing and a CPC.
The SWA must be earthed somewhere - making it a (Circuit) Protective Conductor - so I'm not sure it can ever be classed as an exposed-conductive-part.
I disagree with this. If a core in the cable is used as a cpc, then the armour is only an extraneous exposed-conductive-part. It can be earthed at one end only (usually the "source" end).
edited to correct typo.
It cannot be earthing (CPCs) because those cables clearly do not provide a path back to earth.
That is clearly not true, as current due to a fault in one of the cables will be carried back down another cable. The armour acts as "conductors in parallel".
presumably the exposed conductive parts are electrically continuous at the supply end.
OK, but isn't that how the copper conductor is used when it is provided in parallel with armour?
well if you are not sure if a green/yellow wire is earthing or bonding, ask what happens if you cut that link ?
1~) would you remove the CPC - the return path for operating the ADS. if the ADS would be disabled, that is a CPC or earthing.
2) would you only remove a conductor that keeps the touch voltage down during a fault but does not remove the ADS - this is bonding,
Of course it could be both or neither.
Mike.
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