Bonding question

[rjp44]

it does not have to be a TT system for this to happen,

How so, surely the earth-neutral bond in a TN system will provide a low enough impedance that the fault current will open any protective device on the fault circuit. What scenario are you thinking about?

 

[poni]

when a PEN gets disconnected or has a high resistance, in somewhere like in a block of flats, where there is one incoming supply and many submains coming of it, if the main earth gets disconnected at the point of origin