TN networks

 In a TN earthing system, one of the points in the generator or transformer is connected with the 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. This arrangement is a current standard for residential and industrial electric systems, particularly in Europe.[6]

The conductor that connects the exposed metallic parts of the consumer's electrical installation is called protective earth (PE; see also: Ground). 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.

separate protective earth (PE) and neutral (N) conductors from the transformer to consuming devices, which is not connected together at any point after the building distribution point.

TN−C

A combined PEN conductor fulfills the functions of both a PE and an N conductor (on 230/400 V systems normally only used for distribution networks)

Combined PE and N conductor all the way from the transformer to the consuming device

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, and the earth and neutral are separated in the service head. 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 via the shortest practicable route to a local Earth-Rod at the source and at each premises, to provide both System Earthing and Equipment Earthing at each of these locations