sockets 16A (internally fused I guess).

Are we talking about sockets with interval overcurrent protection - something like this: https://www.cef.co.uk/catalogue/products/1150765-16a-2p-e-110v-unswitched-socket-with-25a-rcd-ip44 (but with an MCB or RCBO instead of an RCCB).

The furthest socket is about 50m away from Transformer.

for voltage drop - 4mm² has a v.d. of around 11mV/A/m so 16A (for one leg of the ring) over 50m would give a v.d. of 8.8V - whereas 5% of 110V is 5.5V - so that looks like a problem even before you consider v.d. in the 230V circuit supplying the transformer.

I suppose that you might be able to arrange the transformer (e.g. via taps) to boost the secondary voltage somewhat, undoing the voltage drop on the 230V side and perhaps increasing the starting voltage on the 110V side, but that wouldn't undo the power losses, so maybe not an ideal solution.

   - Andy.

sockets 16A (internally fused I guess).

Are we talking about sockets with interval overcurrent protection - something like this: https://www.cef.co.uk/catalogue/products/1150765-16a-2p-e-110v-unswitched-socket-with-25a-rcd-ip44 (but with an MCB or RCBO instead of an RCCB).

The furthest socket is about 50m away from Transformer.

for voltage drop - 4mm² has a v.d. of around 11mV/A/m so 16A (for one leg of the ring) over 50m would give a v.d. of 8.8V - whereas 5% of 110V is 5.5V - so that looks like a problem even before you consider v.d. in the 230V circuit supplying the transformer.

I suppose that you might be able to arrange the transformer (e.g. via taps) to boost the secondary voltage somewhat, undoing the voltage drop on the 230V side and perhaps increasing the starting voltage on the 110V side, but that wouldn't undo the power losses, so maybe not an ideal solution.

   - Andy.