Picking up on Mike's point:

Also electrode-less PEN fault sensing  relies on detecting the L-N voltage going wild during the fault. It is not perfect - there will be a range of conditions where the earth voltage rise may be dangerous without the LN voltage going far enough out of limits to guarantee the fault being detected.

There was a discussion here open-pen-detection-for-722-411-4-1-iv which attempted to illustrate the problem with these devices are used downstream of 3-phase systems - under certain conditions it can permit persistent touch voltages far in excess of the 50V that's normally the limit. On totally single phase systems (e.g. rural caravan site fed from a single phase pole transformer) the risks should be less but those installations are very often TT anyway.

   - Andy.

Picking up on Mike's point:

Also electrode-less PEN fault sensing  relies on detecting the L-N voltage going wild during the fault. It is not perfect - there will be a range of conditions where the earth voltage rise may be dangerous without the LN voltage going far enough out of limits to guarantee the fault being detected.

There was a discussion here open-pen-detection-for-722-411-4-1-iv which attempted to illustrate the problem with these devices are used downstream of 3-phase systems - under certain conditions it can permit persistent touch voltages far in excess of the 50V that's normally the limit. On totally single phase systems (e.g. rural caravan site fed from a single phase pole transformer) the risks should be less but those installations are very often TT anyway.

   - Andy.