Revision Standard - Active.The neutral grounding of single- and three-phase ac electric-utility primary distribution systems with nominal voltages in the range of 2.4 kV 34.5 kV is addressed. Classes of distribution-systems grounding are defined. Basic considerations in distribution-system grounding concerning economics, control of temporary overvoltages, control of ground-fault currents, and ground relaying are addressed. Also considered is the use of grounding transformers, grounding of high-voltage neutral of wye-delta distribution transformers, and interconnection of primary and secondary neutrals of distribution transformers.