A daft question, or not....!

[polo1]

Three core SWA installed as a new circuit on a TNS supply. Both ends of the SWA are earthed.
Would you/ is it acceptable to include the armour in the R1+R2 calculation (ie in parallel with the core being used as cpc) or should measurement simply be between cores?

 

[Leesparkykent]

No you would not include the armour, it’s an exposed conductive-part.
Just the same as you would not include metal conduit, trunking, cable tray, etc.

The armour is not an exposed conductive part. It's conductive but not exposed as it's covered by a sheath.

 

[Deleted member 26818]

The armour is not an exposed conductive part. It's conductive but not exposed as it's covered by a sheath.

That’s ok then.
I guess neither are back boxes buried in walls?

 

[Leesparkykent]

That’s ok then.

what's ok?

 

[Simonslimline]

The armour is not an exposed conductive part. It's conductive but not exposed as it's covered by a sheath.

Guidance not 8 refers to the armouring as being an exposed conductive part.

Something to do with the gland?

 

[Leesparkykent]

Guidance not 8 refers to the armouring as being an exposed conductive part.

Something to do with the gland?

Yeah if a brass gland is used then the brass gland is an exposed conductive part unless covered by a shroud. If it's covered by a shroud then it's just a conductive part.

 

[ipf]

Sorry you don’t think I am being real.
Sidestep what?
I think what you should really be asking, is what to do if conduit or trunking is used as a CPC.

Why should I be asking it? No problem, as far as I'm concerned....or the regs.
I'm sure I wouldn't use cable tray as a cpc, though. Unlike an swa, the wiring's not fully contained.

 

[Richard Burns]

GN8 states (for an SWA with inadequate armour csa to be used as a cpc) that where the armour is earthed and there is also an internal core used as the cpc that the current division between the two parallel conductors cannot be determined and so the separate core should be sized as a stand alone conductor.

Therefore when measuring R1+R2 the armour should not form part of the resistance measurement as the internal core must meet the requirements on its own. Obviously the armour will lower the resistance and presumably assist disconnection but cannot be relied upon.

 

[polo1]

At last Richard, the answer!
In the particular case which prompted the op, the SWA armour, the equivalent csa would have allowed it to be used as the cpc, but with the third core present, not required to.