It possible that Alan has got an untypical installation in Mayenne.
But in a typical TT system the local Protective earth is connected to a ground electrode and notbonded to the neutral at any place. (It is forbidden!)
So any current taking the "earth path" has to enter the ground via local electrode and leave via transformer electrode.
So impedancies (is that English, = sum of all inductive, ohm and capacitive resistors in a loop) will be often 50 ohms or more in what we call the "fault loop". As Voltage against ground in France is 230 V (Belgium often 133V) a current of 230 V/50 Ohm = 4,6 Ampere will result. For any fuse or breaker this will be just a normal load.
So it is quite obvious that the only way to guarantee 0.4 seconds until circuit is switched off (harmonized European norms) can be achieved by means of one or nowadays two RCD in a row.
@ Alan Btw You mixed two locations: Sable d'Olonnes and Île d'Oléron
PS: As to France, I heard that formally it is not TT but IT, as often an impedance is between transformer neutral and transformer ground electrode. Usually this is to compensate capacities of the pole-mounted, but isolated cables they use. But practically it works as TT, as long as a definite voltage and current against ground is guaranteed.
