Certainly a very odd set of words.


If I had to guess (and this really is a guess - more based on what I think it might mean rather than what it says)...


By 'extraneous-conductive-parts not connected to a protective conductor, through which a fault between line and earth may occur' - I'm guessing they mean the earthing system downstream of the PEN break - which is now just Earthed by some incidental connection with true Earth (bonding to some extraneous-conductive-part say) and separated from the functioning PEN conductor by the fault.


If there was a L-PE fault downstream of the PEN break then the fault loop would include this 'incidental' resistance to Earth at the consumer/fault end (R_E) and the source electrode(s) (R_B) at the supply end in series (rather like a TT system) - with practically the entire supply voltage (U_o) shared across both electrodes.


So I think what they're trying to achieve is that the supply star point isn't raised by more than 50V above true earth - presumably for the benefit of other installations still connected to the PEN.


The situation sounds not unlike the TT systems with an uncleared earth fault that Alan mentions from time to time.


Anyhow that's my complete guess for the day. I wouldn't be at all surprised if I'd got it completely wrong.


   - Andy,

Certainly a very odd set of words.


If I had to guess (and this really is a guess - more based on what I think it might mean rather than what it says)...


By 'extraneous-conductive-parts not connected to a protective conductor, through which a fault between line and earth may occur' - I'm guessing they mean the earthing system downstream of the PEN break - which is now just Earthed by some incidental connection with true Earth (bonding to some extraneous-conductive-part say) and separated from the functioning PEN conductor by the fault.


If there was a L-PE fault downstream of the PEN break then the fault loop would include this 'incidental' resistance to Earth at the consumer/fault end (R_E) and the source electrode(s) (R_B) at the supply end in series (rather like a TT system) - with practically the entire supply voltage (U_o) shared across both electrodes.


So I think what they're trying to achieve is that the supply star point isn't raised by more than 50V above true earth - presumably for the benefit of other installations still connected to the PEN.


The situation sounds not unlike the TT systems with an uncleared earth fault that Alan mentions from time to time.


Anyhow that's my complete guess for the day. I wouldn't be at all surprised if I'd got it completely wrong.


   - Andy,