As the title says, if a generator is providing a TNS earthing system connected to a transportable structure through a detachable connection, why does AS3001 state:
Isolation of the protective earth conductor. No fixed connection shall be made between the protective earthing conductor and the general mass of the earth, e.g. by means of a driven electrode. No connection shall be made between any live (active or neutral) conductor and the protective earthing conductor of the electrical installation.
Is there a safety reason? When the transportable structure is metal and it sits on the the ground, isn't that just another form of earthing? Why would it be different if there was an extra earth electrode?