Ground fault protection in low voltage solidly grounded wye systems, need for protection and the need for reliability

Reliable power distribution systems require adequate protection and adequate protection requires reliable protection systems. The need for ground fault protection in low voltage solidly grounded wye systems is well documented in literature, standards and has been part of the national electrical code (NFPA 70) since 1971. The potential effect of ground fault protection on system reliability is a realistic concern, hence the various references indicating when ground fault protection is to be used and not to be used or recommended. How to mitigate the potential negative effects on system reliability is treated in article 517.17 of NFPA 70 (2005). Recent changes in NFPA 70 have made the complexity of LV ground protection and system reliability more prominent. This paper will provide an overview of why LV ground fault protection became the standard we take for granted today. Additionally, the author will summarize some of the key descriptions of arcing fault in industry literature as well as descriptions in current standards that define the devices and protection commonly used today. Key aspects of how devices respond to fault current will be discussed. Finally, the author will provide an analysis of selectivity and system reliability issues involving ground fault protection.