TT, TN‑C‑S, IT, TN-C Earthing Arrangements

One area that always created a stumbling block was in remembering earthing arrangements since at the time the lettering did not create links. Using Tony Buzan's books however I have found that I can remember these by producing mind links.

In Latin earth is called Terra (Terre in French ) so we get Terra Firma, on solid ground.

So the first letter denotes if the supply is connected to Earth or Terra with the capital letter T. If insulated from earth then I is used, I for insulated.

The second letter denotes where the consumers earth is connected to. So T would indicate to earth. So TT means that the supply transformer star point is connected to earth and the consumers equipment is also connected to earth using earth spikes etc.

In an IT system the supply transfomer has no connection to earth but the consumers equipment is connected to earth using earthing spikes etc.

N stands for neutral and thus in a TN system the consumers earth is connected to earth via the neutral of the supply.
TN‑S is where the earth and neutral are fed back to the supplier with seperate conductors.
TN‑C is where the earth and neutral are fed back to the supplier using one conductor.
TN-C-S is where the earth and neutral are fed back to the supplier using one conductor but this time the connection of the earth to the neutral is not directly made at the consumers end thus there are two seperate conductors from the premises.

There is good article on this in pdf format form the IEE