All ground symbols are assigned with same node “0”. View → Netlist, and you can confirm from there.
This post we discussed concept of ground and isolation in simulation
Transformer secondary: grounded/1Meg/or nothing? - QSPICE - Qorvo Tech Forum
Isolation means no current flow between two “isolated” circuits. GND is required in “isolated” circuits as every node must find a relationship to 0V potential (GND) in spice simulation. But unlike real life, adding a GND in simulation doesn’t mean two part not isolate! As long as no current flow between, they are electrically isolated.
Here is an example: E1 isolates the circuit into two parts. V2 is used to establish a ground (0V) reference for nodes V(b) and V(c). As the two parts are isolated, V2 is measured with 0A. You can assign any voltage to V2, but it won’t affect the differential voltage between V(b) and V(c), only their absolute potential.
If you don’t add V2 in this circuit, Qspice will report a floating node and set a gshunt for you. This is what we discussed in the link provided above.
