Interesting question - the largest steady state voltage I'd expect between a CPC and the terra-firma ground in a non-fault state would be about half the possible  L-N loop voltage drop, and that assumes no cancellation of current from other phases,  and that the earth electrodes and so on  at the substation end have a lower impedance than any intermediate electrodes or bonded services.

I have on occasion used small 12V lamps between L and E in  a TT system to indicate trouble, and normally at most they light dimly, say half a dozen volts, and the only time they light brightly or blow, is when there have been serious faults.

Short transients, like brief under-voltages, I'd associate with faults and fuses blowing, or inrush of heavy machinery, but again, I'd expect a PEN to rise no more than the coressponding  live voltage falls, and probably rather less  in the majority of credible faults.

A 70V figure  is sometimes quoted for things like supplies to traffic lights, as the rise of earth permitted if the supply fails and in effect becomes a 230v version of single wire earth return supply- this is important, as no  current ADS can detect such a condition - and this figure drives a specification as to how good the local earthing must be.


If we want an absolute figure for an upper bound, assume the statutory limits of mains supply, 207 to 253 volts (230 =/- 10%) and assume 253 at the end with the supply transformer and the good earth, and 207 at the load, and assume a single phase line pair - so 46v drop, 23 volts dropping down the live, and 23V dropping 'up' the neutral, as towards the load, the voltage gets closer to the live.


This would be a really bad system but maybe meeting the rules just about.  Personally I have never seen a 23V offset, and probably not really seen more than 12v, in any system not being abused or suffering with a supply fault.


There are significant gradients in voltage across the earth, but around an electrode, the voltage is only really distorted a lot for about  a rod radius.  - in terms of step voltage danger, banning bare feet for an electrode length around the electrode is normally enough. There are tricks like gravel that can reduce the step voltage risk,, in 2 ways, firstly because it is not a good conductor, and will not support puddles,  and secondly because it us unpleasant to stand on without thick soled footwear, so there is less likely to be any one there.

Assuming the ground is uniform, and has no buried conductive material, the voltage contours are more or less independent of the soil resistance, the current varies, but the distance to half voltage is largely unaffected.

Interesting question - the largest steady state voltage I'd expect between a CPC and the terra-firma ground in a non-fault state would be about half the possible  L-N loop voltage drop, and that assumes no cancellation of current from other phases,  and that the earth electrodes and so on  at the substation end have a lower impedance than any intermediate electrodes or bonded services.

I have on occasion used small 12V lamps between L and E in  a TT system to indicate trouble, and normally at most they light dimly, say half a dozen volts, and the only time they light brightly or blow, is when there have been serious faults.

Short transients, like brief under-voltages, I'd associate with faults and fuses blowing, or inrush of heavy machinery, but again, I'd expect a PEN to rise no more than the coressponding  live voltage falls, and probably rather less  in the majority of credible faults.

A 70V figure  is sometimes quoted for things like supplies to traffic lights, as the rise of earth permitted if the supply fails and in effect becomes a 230v version of single wire earth return supply- this is important, as no  current ADS can detect such a condition - and this figure drives a specification as to how good the local earthing must be.


If we want an absolute figure for an upper bound, assume the statutory limits of mains supply, 207 to 253 volts (230 =/- 10%) and assume 253 at the end with the supply transformer and the good earth, and 207 at the load, and assume a single phase line pair - so 46v drop, 23 volts dropping down the live, and 23V dropping 'up' the neutral, as towards the load, the voltage gets closer to the live.


This would be a really bad system but maybe meeting the rules just about.  Personally I have never seen a 23V offset, and probably not really seen more than 12v, in any system not being abused or suffering with a supply fault.


There are significant gradients in voltage across the earth, but around an electrode, the voltage is only really distorted a lot for about  a rod radius.  - in terms of step voltage danger, banning bare feet for an electrode length around the electrode is normally enough. There are tricks like gravel that can reduce the step voltage risk,, in 2 ways, firstly because it is not a good conductor, and will not support puddles,  and secondly because it us unpleasant to stand on without thick soled footwear, so there is less likely to be any one there.

Assuming the ground is uniform, and has no buried conductive material, the voltage contours are more or less independent of the soil resistance, the current varies, but the distance to half voltage is largely unaffected.