Emergence of earthing systems
These systems are the result of a lengthy evolution guided by the search for increased personnel protection. Between 1880 and 1920, transmission and distribution of electrical power took place in «unearthed neutral». Lines are uninsulated, placed out of reach, supported by insulators; no points of the network are deliberately earthed. In homes, voltage is 100/110 V AC. Throughout this period, fuses blow and persons «receive Electric Shocks» and few people were electrocuted.
Today the 3 system earthing such as defined in IEC 60364 and French standard NF C 15-100, are:
Earthed neutral -TT
Exposed-conductive parts connected to neutral -TN
Unearthed (or impedance-earthed) neutral –IT
Those three earthing systems are created to ensure the protection of persons and property
