Earthing or bonding ?

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.

Plus, of course, a CPC may also be used as a Bonding Conductor - which is also a protective conductor.

geoffsd said:

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.

geoffsd said:

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.

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.

geoffsd said:

I presume you are not proposing that the armour may sometimes be left totally unearthed.

Yes, there are occasions when this might happen, BUT not, of course, if the cable is buried, where the armour must be both earthed and suitable to act as a protective conductor.

geoffsd said:

Therefore when earthed it acts as a CPC for the internal circuit in case of, for example, striking by a spade.

Or an exposed-conductive-part ... BS 7671 is not clear on this. If the armour is earthed at one end only, it's not providing cpc function to the connected equipment or circuit downstream of the cable, and therefore another core (or single core cable) is the cpc ...

geoffsd said:

How can it be an extraneous-conductive-part? Extraneous-c-ps are not earthed.

Apologies, mis-type, exposed-conductive-part as above. cpc's definitely are earthed in TN, TT and IT systems ... via the MET and the main earthing conductor!

geoffsd said:

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.

Agreed, I think it's an exposed-conductive-part all the time (for LV use), BUT only a cpc when it's connected to cpc's at both ends of the cable (an exposed-conductive-part is permitted to be a protective conductor).

"Agreed, I think it's an exposed-conductive-part all the time (for LV use), BUT only a cpc when it's connected to cpc's at both ends of the cable (an exposed-conductive-part is permitted to be a protective conductor)."

I suppose it is semantics, but:

As an exposed-c-p, you must think a live conductor is liable to make it live during a fault and a person is likely to contact it?

A cpc to a Class II item is not connected at both ends; does that mean it ceases to be a cpc protecting the circuit?