This sort of thing can occur - what are we looking at there actually, as there seem to be 4 wires on the nearby LV pole and yet only 2 to the TX ? or is there concentric cable in use ?

Is that 'just' the HV earth for the transformer can and core, or is it also the reference for the LV system neutral as well ?

Loss of HV earth or a combined earth can be very nasty on  non 3-phase  transformer as there are several nano-farads between the HV windings and the core, so even  when all is working well, there is a non zero current in that lead, and it has quite a large open circuit voltage behind it, perhaps half of the HV phase to ground voltage.

On a 3 phase system, the HV to  earth leakages cancel  to a degree.

Loss of just the LV earth can, as you describe lead to some odd problems with clearing faults, and things that should be at or near earth potential becoming dangerous when there is a fault elsewhere.

The tacit BS7671 assumption that the network is perfect upstream of the company fuse or whatever  is  not always correct is it ?

Mike

mapj1 said:

what are we looking at there actually, as there seem to be 4 wires on the nearby LV pole and yet only 2 to the TX ? or is there concentric cable in use ?

Just a single-phase tx with 2 line and 2 neutral. The LV line goes quite some distance.

mapj1 said:

what are we looking at there actually, as there seem to be 4 wires on the nearby LV pole and yet only 2 to the TX ? or is there concentric cable in use ?

Just a single-phase tx with 2 line and 2 neutral. The LV line goes quite some distance.