Power0020,
Due to high earth fault currents RCD devices are not allowed in TN-C systems. Per IEC60364, in a TN-C earthing system the earth fault current is
taken back to the source by the PEN conductor in contrast to PE conductor of a TN-C-S earthing system. That means at each utilization equipment,
the N terminal has to be bonded to the E terminal. With time if this bonding develops a high resistance to the earth fault loop impedance then,
the tripping time of the overcurrent device during an earth fault will be longer (more energy is released at the fault point) and it might
create a fire within the installation. Therefore, at installations or buildings where there is a fire risk, TN-C earthing is not acceptable.