Replacing fused subpanel with breakers subpanel
If you put in a sub-panel you must disconnect the ground/nuetral connection in the subpanel and run a wire between the two grounding bars. its the same code no matter where you live. There can only be one ground in the house.You can run another wire between the nuetral bus bars also. This prevents a stray voltage loop .
you are way off base. the maximum load for 120 volts X 15 amps is 1800 watts. You need 120 volts X 20 amps to get 2400 watts. This willl require 12 guage wire. Any shortcuts is hazardous.