Testing if supplementary bonding is required.

Quite so. There are a few points to consider.

In a TT system, during an L-E fault, the cpc, and any wires to the electrodes and anything connected to that, normally  rise to a significant fraction of the full 230V, if you could measure it with a long lead, relative to the true terra-firma earth outside at a point  far away from any electrode.

This assumes that the other electrode in the loop, the one at the substation end, where the current comes back up again, is in good order, and most of the voltage drop is at the load end electrode. Sometimes it isn't, and that can make the N-E voltage move for other customers on the same substation.


Around each electrode is a 'fried egg shape' of approximate circles of increasing voltage as you approach the electrode, however, for an electrode of length l, by the time you are a distance of a few times 'l'  away you are far enough out that this gradient is not dangerous. However it is not unknown for cows and horses and other 'long wheelbase' animals to be shocked, if one set of hooves is much nearer the electrode than the other, so they straddle zones of  different voltage. A 'step voltage' shock is also possible for humans, but those who wear shoes or only take small steps do not normally notice.)

What happens indoors rather depends which "ground" - you will probably  not experience much of a shock, unless the floor has been removed and you are standing on bare earth, as all of the house radiators, heating pipes, earthed appliances will all rise with the TT electrode voltage, but this is where the few  truly earthed things (i.e connected to terra-firma, and far away) like phone lines and cable TV feeders, suddenly become dangerous.

The saving grace is indeed the RCD.

Mike.

Quite so. There are a few points to consider.

In a TT system, during an L-E fault, the cpc, and any wires to the electrodes and anything connected to that, normally  rise to a significant fraction of the full 230V, if you could measure it with a long lead, relative to the true terra-firma earth outside at a point  far away from any electrode.

This assumes that the other electrode in the loop, the one at the substation end, where the current comes back up again, is in good order, and most of the voltage drop is at the load end electrode. Sometimes it isn't, and that can make the N-E voltage move for other customers on the same substation.


Around each electrode is a 'fried egg shape' of approximate circles of increasing voltage as you approach the electrode, however, for an electrode of length l, by the time you are a distance of a few times 'l'  away you are far enough out that this gradient is not dangerous. However it is not unknown for cows and horses and other 'long wheelbase' animals to be shocked, if one set of hooves is much nearer the electrode than the other, so they straddle zones of  different voltage. A 'step voltage' shock is also possible for humans, but those who wear shoes or only take small steps do not normally notice.)

What happens indoors rather depends which "ground" - you will probably  not experience much of a shock, unless the floor has been removed and you are standing on bare earth, as all of the house radiators, heating pipes, earthed appliances will all rise with the TT electrode voltage, but this is where the few  truly earthed things (i.e connected to terra-firma, and far away) like phone lines and cable TV feeders, suddenly become dangerous.

The saving grace is indeed the RCD.

Mike.