What is the legal term a TN-C-S system? When Talking about an elecrical system?

Took this straight from Wiki -- it was a WHOLE lot easier than typing it from scratch and their illustrations are very helpful. If you'd like to see the illustrations that go with it, head for http://en.wikipedia.org/wiki/Earthing_sy...





The Wiki starts out with a description of TN grounding systems, and then goes on to describe the variations, including TN-C-S.








In a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star point in a three-phase system. The body of the electrical device is connected with earth via this earth connection at the transformer.





The conductor that connects the exposed metallic parts of the consumer is called protective earth (PE). The conductor that connects to the star point in a three-phase system, or that carries the return current in a single-phase system, is called neutral (N). Three variants of TN systems are distinguished:








TN‑S : PE and N are separate conductors that are connected together only near the power source.





TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.





TN‑C‑S : Part of the system uses a combined PEN conductor, which is at some point split up into separate PE and N lines. The combined PEN conductor typically occurs between the substation and the entry point into the building, whereas within the building separate PE and N conductors are used. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of broken neutrals - with a similar system in Australia being designated as multiple earthed neutral (MEN).





It is possible to have both TN-S and TN-C-S supplies from the same transformer. For example, the sheaths on some underground cables corrode and stop providing good earth connections, and so homes where "bad earths" are found get converted to TN-C-S.

What is the legal term a TN-C-S system? When Talking about an elecrical system?
can you explain it further what you mean