Foreword?This guide is part of a series on neutral grounding in electrical utility systems. When the series of documents are approved and published@ they will replace IEEE Std 143-1954 @ IEEE Guide for Ground-Fault Neutralizers@ Grounding of Synchronous Generator Systems@ and Neutral Grounding of Transmission Systems. IEEE Std 143-1954 is a revision of AIEE No. 954@ Oct. 1954@ which was a compilation of the following three AIEE Transaction papers: AIEE Committee Guide Report@ ??Application of Ground-Fault Neutralizers@?? AIEE Transactions (Power Apparatus and Systems)@ vol. 72@ pt. III@ pp. 183?C190@ Apr. 1953. AIEE Committee Report@ ??Application Guide for the Grounding of Synchronous Generator Systems@?? AIEE Transactions (Power Apparatus and Systems)@ vol. 72@ pt. III@ pp. 517?C530@ June 1953. AIEE Committee Report@ ??Application Guide on Methods of Neutral Grounding of Transmission Systems@?? AIEE Transactions (Power Apparatus and Systems)@ vol. 72@ pt. III@ pp. 663?C668@ June 1953. The contents of Parts I?CV of the revision of IEEE Std 143-1954 are based on the foregoing documents but are amplified and updated with new material from the IEEE tutorial course@ ??Surge Protection in Power Systems?? [(79H)144-6-PWR]@ and other sources. Part III covers the considerations and practices relating to grounding of generating station auxiliary power systems. The related parts are: Part I@ Introduction (Theory and performance characteristics of classes of neutral grounding); Part II@ Grounding of Synchronous Generator Systems; Part IV@ Distribution; and Part V@ Transmission Systems and Subtransmission Systems. ScopeThis guide summarizes the general considerations in grounding of generating station auxiliary power systems and discusses the factors to be considered in selecting between the appropriate grounding classes and in specifying equipment ratings. This guide applies to both medium-voltage and low-voltage auxiliary power systems. Grounding and bonding to achieve practical safeguarding of persons is fulfilled by electrically connecting equipment frames and enclosures and interconnecting wiring raceways to the station grounding network (see IEEE Std 142-1991 1)@ as required by ANSI C2-1993. References to safety in this guide mean freedom from equipment damage. The emphasis is on reliability and availability of auxiliary system service achieved through control of ground-fault currents and transient overvoltages. This guide is specifically written for electrical utility systems and does not recognize the neutral grounding requirements for dispersed storage and generation. These requirements must recognize the restrictions imposed by the specific network to which the dispersed storage or generation is connected. Neutral grounding of dispersed storage and generation needs to be coordinated with the electrical utility system. 1Information on references can be found in clause 2.