Kelly Marie Angel:
Why did you disconnected the stables when the fault was in a cottages submain?
The fault is at the stables - they have connected 'L3' to ground very solidly, and their RCD has not fired.
Because the earth at the DNO transformer has a higher electrode resistance than the stables, the L3 voltage goes down to near terra-firma potential, and the star point of the transformer goes up, there is still 240V between them,
(i.e. the two electrode to terra-firma resistances are now in series, with one to N one to L3, but the terra-firma earth between them is better connected to L3.)
Now anyone on the same Tx sees
L3- E 0V,
N -E 240V,
L2 -E 400V
L1-E 400V
All the phase to phase and neutral voltages remain correct, just the main ground is moved from the centre of the star, to one corner.
The original caller presumably had a single phase supply and had say L1, N and a local terra-firma earth.
Mike.
Had there been any PME users on that transformer it would have been another story altogether.
The advantage we had as the DNO, is that we had the ability to look at the whole village, and disconnect properties until we found out who had the problem.
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