The paper defines different effects of iterative earthing on N line and PE line through the analysis on iterative earthing in earthing modes of TN systems,and discriminates iterative earthing from N-line iterative earthing.

Based on the standard of grounding wire selection,the methods of PE wire cross section selection for different low-voltage distribution system are introduced.

An analysis is made of the mechanisms of high N-PE voltage formation,which are induced by pure resistance,earth circuit loop,and common impedance,in connection with the common faults resulted from high N-PE(neutral and protected earth conductor) voltage encountered in the operational lightning protection for the information system.