scope:

This part of the guide is concerned with 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. For the purpose of this guide, the term "distribution" includes the substation providing power to distribution feeders, the distribution feeders, and the distribution transformers providing service at utilization voltages. The scope of this guide does not include the grounding of the low-voltage secondary systems supplied by distribution transformers or consumer-owned facilities that are covered by other documents such as the National Electrical Code® (NEC®) (NFPA 70, 2011 Edition)¹ [B28]²

Purpose

The purpose of this guide is to provide information regarding neutral grounding of electric-utility primary distribution systems with nominal voltages in the range of 2.4 kV - 34.5 kV. Classes of distribution systems grounding are defined while basic consideration is given to economics, control of temporary overvoltages (TOVs), control of ground fault currents, and ground relaying.

¹ National Electrical Code, NEC, and NFPA 70 are registered trademarks of the National Fire Protection Association, Inc.

² The numbers in brackets correspond to those of the bibliography in Annex C.