Decoding the Earthing Types

First letter	T	Connected directly to main earth at a certain point in the power system, normally at the supplying transformer (T = Terra (Earth)).
	I	The power system is insulated from earth or connected to earth through a sufficient high impedance (I = Isolated).
Second letter	T	The exposed conductive parts are connected directly to earth e.g. the UPS chassis disregarding whether the power system is earthed or not.
	N	The exposed conductive parts e.g. the UPS chassis are connected directly to earth at the main earthing point (N = Neutral).
Additional letters	S	The Protective Conductor (PE) and Neutral Conductor (N) are two different and separate conductors (S = Split).
	C	The Protective Conductor (PE) and Neutral Conductor (N) are one common conductor (PEN) (C = Common).