Andrew Gabriel wrote:

Single
2.5T&E-----------DS-------JB----------FCU (300W load)
from CU (700W) |
(20A MCB) max |
|
2.8kW load

That's better.

If it is a water heater over 20 litres (IIRC)

15 litres.

Also the floor area served by a 20 A radial circuit shouldn't exceed 50 m^2.

--
Andy