currently chewing though Security capacity and network reinforcement and apportionament calculations….but I cant quite work out how to define them given my circumstances.

There's an existing 15kva transformer on a pole serving 5 households already (I reckon that's way below the capacity that should be there).
Ive been told that my additional connection (single phase, 18kva) means that the transformer will need upgrading to a 50kva. Understandable.
BUT, I want according to the apportionment rules I might have to stump up a lot of cash, whereas I reckon they should have put a bigger box up long before my additional connection came along.

Can someone help me with the calc for the network capacity that SHOULD be in place, and so the incremental capacity Im asking for should be lower as a proportion of the new capacity?

For example, if I assume that at the 4th new domestic connection they should have upped the transformer to 50kva to serve 4x18kva supplies, then I shouldnt have to pay for the upgrade now?

EDIT: Doh wrong forum, cant edit, mods!