Hi, Alan and OMS.


In my text that you quoted, please note that "by this definition" refers to a BS7671 definition of PEN (and of protective conductor PE) that I gave in an earlier sentence. The conductor in question in PNB, between the transformer neutral point and the switchboard + earth electrode, connects an earth electrode and a neutral point: so the definition says it's a protective conductor. And it connects to the source neutral and 'contributes to the transmission of electrical energy', so it's a neutral conductor. By being both of these, it's a PEN.  The definition of PE seems a little permissive.


Then I went on to note that by this same definition it seems that even in a TT system with its first system earth electrode some distance along the neutral, the neutral conductor between that electrode and source neutral would deemed a PEN (regardless of whether the network owner offers installation earthing to the neutral). The BS7671 definition of PEN isn't linked explicitly to TNCS, which was initially a surprise.

 

OMS  No it's not - by any definition it would need to be carrying load or imbalance current and earth fault current

... which is what it does in the cases I gave (of certain conductors in PNB and TT systems): it carries load/imbalance currents and is in the earth fault loop. 


The reason I laboured the matter of "if the neutral point is where the three phases' neutral ends meet" is because I thought someone would claim that the load-end of the PNB "conductor in question"  is also just a part of the neutral point. That's a neat way to avoid the strange definition of this conductor, but it doesn't strike me as the spirit of the definitions.


I don't claim anything about the BS7671 definition being sensible, or the best, or in keeping with people's 'instinct'. I was just interested to see the divide between what many of us consider the common-sense definitions of TNCS/TNS/PEN and what appears to come from an influential standard.  I know you don't agree with PNB being TNCS: I also suggested TNS to be the sensible option in my first posting in this topic.  But if you can show based on BS7671 definitions of PEN rather than your own or some other undeclared ones that the two controversial PENs mentioned above are not PENs, I'd be interested to know!  It's seldom that I get into a discussion of definitions rather than actual technical details of good and bad points of a system, but this case surprised me into a little interest.

Hi, Alan and OMS.


In my text that you quoted, please note that "by this definition" refers to a BS7671 definition of PEN (and of protective conductor PE) that I gave in an earlier sentence. The conductor in question in PNB, between the transformer neutral point and the switchboard + earth electrode, connects an earth electrode and a neutral point: so the definition says it's a protective conductor. And it connects to the source neutral and 'contributes to the transmission of electrical energy', so it's a neutral conductor. By being both of these, it's a PEN.  The definition of PE seems a little permissive.


Then I went on to note that by this same definition it seems that even in a TT system with its first system earth electrode some distance along the neutral, the neutral conductor between that electrode and source neutral would deemed a PEN (regardless of whether the network owner offers installation earthing to the neutral). The BS7671 definition of PEN isn't linked explicitly to TNCS, which was initially a surprise.

 

OMS  No it's not - by any definition it would need to be carrying load or imbalance current and earth fault current

... which is what it does in the cases I gave (of certain conductors in PNB and TT systems): it carries load/imbalance currents and is in the earth fault loop. 


The reason I laboured the matter of "if the neutral point is where the three phases' neutral ends meet" is because I thought someone would claim that the load-end of the PNB "conductor in question"  is also just a part of the neutral point. That's a neat way to avoid the strange definition of this conductor, but it doesn't strike me as the spirit of the definitions.


I don't claim anything about the BS7671 definition being sensible, or the best, or in keeping with people's 'instinct'. I was just interested to see the divide between what many of us consider the common-sense definitions of TNCS/TNS/PEN and what appears to come from an influential standard.  I know you don't agree with PNB being TNCS: I also suggested TNS to be the sensible option in my first posting in this topic.  But if you can show based on BS7671 definitions of PEN rather than your own or some other undeclared ones that the two controversial PENs mentioned above are not PENs, I'd be interested to know!  It's seldom that I get into a discussion of definitions rather than actual technical details of good and bad points of a system, but this case surprised me into a little interest.