Voltages of floated outputs of an isolated transformer
That there is no galvanic connection to earth does not mean there is no capacitative connection to earth. E.g. the transformer windings build a capacitance if the core is earthed. Wires could run close to grounded parts etc. This capacitative source impedance should be rather big, i.e. if a device of 20 or more Watt is connected to a phase and Earth, the voltage must drop.