Hi.
Generally speaking I don't think floating land is necessary. It is possible to calculate circuits without it.
But especially for stubborn people I have created a model of floating ground and a symbol for it. Everything is in my large collection of models.
Here are the contents of the model:
.subckt GNDFLOAT 1 Cp=1pF Rp=1G
c 1 0 {Cp} Rpar={Rp}
.ends GNDFLOAT
Make your own symbol for this model.
There can be many such floating grounds in the schematic.
Real floating grounds have this equivalent.
With galvanic isolation, there is always a small capacitance between windings. When optocouplers are used, they also have parasitic capacitance in them.
My floating ground is better than the commonly used high impedance resistors for simulation.
