BS 7671 Query - Earthing of line conductors

[Charlie_Don't_Surf]

I'm working my way through the BS 7671 handbook and the course I've bought which accompanies the exam, in preparation for the latter.

I have now come across, in a couple of places, regulations which require under some circumstances, for line conductors to be earthed. for example:

"411.4.2 The neutral point or the midpoint of the power supply system shall be earthed. If a neutral point or midpoint is not available or not accessible, a line conductor shall be earthed."

(Admittedly, it indicates this aspect is the responsibility of the distributor, so perhaps this is something beyond what I need to understand, being as I'm working solely on the consumer side of things).

My question is - how could you earth a line conductor? Surely this would create a big bang.

I know I will probably end up looking stupid for asking this question, but if it improves my understanding, I'll take the hit

 

[Marvo]

A 'line' conductor isn't necessarily a 'live' conductor. A line conductor is any conductor that forms part of a circuit so the neutral is also a 'line' conductor for example.

I'm not UK based and I don't work to UK regs so wait for someone else to confirm but I'm guessing the reg you've quoted refers to the supply to a premises and not a final circuit within an installation. I'd also guess it's about adding an extra earth spike at the premises to mitigate risk of a suppliers PEN fault and bolster the earth on a PME'd TN C S supply and maybe also TN S supply.

From what I've seen of previous discussions I don't think it's an actual requirement in the UK as much as a recomendation or a possibility in certain circumstances although again maybe wait for a UK member to confirm as the regs may have been updated..

 

[davesparks]

A 'line' conductor isn't necessarily a 'live' conductor. A line conductor is any conductor that forms part of a circuit so the neutral is also a 'line' conductor for example.

Other way round, all line conductors are live conductors, but not all live conductors are line conductors.

A live conductor is any conductor which carries current under normal conditions, ie. line and neutral carry current under normal conditions and so both are live conductors.