The purpose of this document is to provide guidance on applying surge testing to ac power interfaces of equipment connected to low voltage (up to 1000 V rms) ac power circuits that are subject to transient overvoltages. These transients may be defined by any applicable document, such as IEEE Std C62.41-1991 or IEC 664-1 (1992). While frequent reference is made to these documents, the application of this guide is not limited to them. In IEEE Std C62.41-1991 , a description is given of the surge environment that can be expected to prevail in low-voltage ac power circuits where no special precautions have been taken to limit transient overvoltages; in IEC 664-1 (1992), a recommendation made to establish a controlled overvoltage situation is justified if there is compliance with appropriate interface requirements, so that maximum overvoltage levels in a descending staircase can be assigned according to a specified overvoltage category where such a category generally reflects the configuration of the power system within a building. The environment description of IEEE Std C62A 1-1991 provides guidance on the waveforms of current as well as voltage surges that can be selected as representative of the environment for different location categories. The recommendations of IEC 664-1 (1992), provide the basis forinsulation coordination. Other standards or specifications for surge withstand capability might also require surge testing to be performed, for which the guidance of the present document may also be applicable. Regardless of the specification, equipment connected to the power system has to be capable of satisfactory operation or survival, or both, under these surge voltages, with or without additional protection. Surge testing is therefore required to demonstrate this capability. The flow chart of figure shows the basic considerations involved in planning and performing surge tests in accordance with the scope of this guide. Note that the assignment of surge withstand levels to various equipment is not included in the scope of this guide. Signal and data lines are also not included in the scope of this guide, but should not be overlooked in the complete evaluation of specific equipment.