In most countries where regulation permits it, TT is preferred for such systems as conventional wiring techniques can be used.
Examples where an IG may be required include radio transmitters where it is not desired for RF currents associated with the antenna and its earthing to enter the mains supply wiring, and in reverse, for sensitive apparatus that should be protected from supply borne interference.
The IG is typically insulated and separate all the way back to the point of earth grounding rod outside of the building.
[2] Until the 1950s, isolated ground domestic mains supplies tended to have no Residual-Current Device (RCD) or Earth Leakage Circuit Breaker (ELCB), and too high a ground impedance to blow a fuse if a live-to-earth fault occurred.
The use of Residual Current Devices (RCDs) or formerly ELCBs with such installs solved this problem.