TN-C-S is fairly similar to standard US practice, TN-C more or less equals the old US 3w dryer hookups.
IT systems are only to be used for separately derived systems not exceeding a certain size, running off their own transformer or generator. As far as I know mostly used for hospital equipment.
TN-C used to be very common in Germany. Imagine an old US house with only 2-prong outlets. Then somebody comes in and puts in 3-prong outlets, running the white wire to the green screw and a white jumper to the silver screw. IMHO scary.
