I've just seen this article in E&T highlighting the increased incidence of reported broken PEN's from 57 in 2003 to 474 in 2021. It seems they are becoming less of a rare event.
David
I've just seen this article in E&T highlighting the increased incidence of reported broken PEN's from 57 in 2003 to 474 in 2021. It seems they are becoming less of a rare event.
David
But if a number of installations downstream of the break have an earth electrode, then Ra(effective) is the parallel resistances of Ra for each installation (assuming no other earthing of the PEN conductor, and no extraneous-conductive-parts).
The good thing about that, is we often hear that there could be high numbers of properties downstream of the break. The higher the number of properties affected, the greater the population at risk ... yet if all had electrodes (and/or extraneous-conductive-parts), the lower Ra(effective) ...
Now, you could also argue that I goes up with the number of installations ... BUT it's also the more likely the break is in a three-phase portion of the distribution network, so if there are n properties downstream of the break, it's only n/3 times as much current (not n times), and also the overall earth electrode resistance requirement is quite possibly lower (depending on the maximum phase imbalance downstream of the break).
Indeed. But on the other hand if you happen to be the only house on the street that's been upgraded to have an additional electrode, I could be a lot higher than your own load... All in all it seems to be of least use in the very circumstances where it should be most useful, which doesn't really recommend it as a solution.
- Andy.
But if a number of installations downstream of the break have an earth electrode, then Ra(effective) is the parallel resistances of Ra for each installation (assuming no other earthing of the PEN conductor, and no extraneous-conductive-parts).
The good thing about that, is we often hear that there could be high numbers of properties downstream of the break. The higher the number of properties affected, the greater the population at risk ... yet if all had electrodes (and/or extraneous-conductive-parts), the lower Ra(effective) ...
Now, you could also argue that I goes up with the number of installations ... BUT it's also the more likely the break is in a three-phase portion of the distribution network, so if there are n properties downstream of the break, it's only n/3 times as much current (not n times), and also the overall earth electrode resistance requirement is quite possibly lower (depending on the maximum phase imbalance downstream of the break).
Indeed. But on the other hand if you happen to be the only house on the street that's been upgraded to have an additional electrode, I could be a lot higher than your own load... All in all it seems to be of least use in the very circumstances where it should be most useful, which doesn't really recommend it as a solution.
- Andy.
. But on the other hand if you happen to be the only house on the street that's been upgraded to have an additional electrode, I could be a lot higher than your own load.
No different to the situation if you're the only house downstream of the break with extraneous-conductive-parts.
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