2 wire overhead feed to 3 phase installation

[EastAnglian]

My mate & I were wondering how the pole-mounted "transformer" is configured on a farm where we've been working.

The overhead supply is very clearly just 2 wires mounted on poles across the field. There is a large transformer mounted on the pole and the presentation at the service head is 3 x 100A fuses, all live, (400V between any two) giving the appearance of a 3P+N supply with TT earthing system.

However, only 2 of the fuses are connected to the meter, and are marked L1 and L3 .... which then go on to power the farm and farmhouse.

So we were musing is this really a 3P supply? If so, how is the transformer configured? There appear to be no moving parts on the pole.

Anybody any good at distribution topologies?

 

[Knobhead]

Two pole split phase. I’d recheck your readings again.

 

[MarkieSparkie]

Hi EA, Like Tony I suspect your measurements are wrong and that there is more likely to be 230V between either Line (L1 or L3) and Earthed Neutral (EN) and 460V between Lines (L1-L3). Both Lines are offset from the Earthed Neutral by half a cycle (180°). This is called a Two Pole, Split Phase Supply, often wrongly called 2 phase or bi-phase. It's common for long supply runs in rural areas, supplying isolated farms in particular, as it saves the DNO the cost of supplying a third line conductor.

 

[EastAnglian]

Thanks guys - I did suspect it wasn't three phase, and the voltage measurements were done quickly some while ago!

So in this arrangement what is the third incoming (non-connected) service fused cable? It is certainly live.