This guide applies to surge-protective devices (SPDs) manufactured to be connected to 50 Hz or 60 Hz ac power circuits rated at 100-1000 V rms. This guide describes the effects on SPDs of power system disturbances occurring in these low-voltage ac power circuits. The disturbances are not limited to surges. The effects of the presence and operation of SPDs on the quality of power available to the connected loads are described. The interaction among multiple SPDs on the same circuit is also described. This guide discusses both voltage and current surges. The current surges discussed in this guide are the result of voltage surges. Current surges that are solely the result of load changes and do not result in voltage increases, such as a short circuit, are not discussed in this guide. An SPD's primary purpose is to provide surge protection. Devices discussed in this guide contain at least one nonlinear component for diverting surge current and/or dissipating surge energy, such as a metal oxide varistor (MOV), silicon avalanche diode (SAD), thyristor, or spark gap. Uninterruptible power supplies (UPSs), ferroresonators, motor-generators, and filters containing only inductive and/or capacitive components are not considered SPDs in this guide. The purpose of this document is to provide information on the interactions between power system disturbances and SPDs that is not readily available in other standards. This document provides summary information on power system disturbances that affect or can affect SPDs. The description of the interactions is intended to inform the potential user of such SPDs as to what can be expected from such devices. Revision Standard - Inactive-Reserved. Information is provided to users and manufacturers of surge-protective devices (SPDs) about the interactions that can occur between SPDs and power system disturbances. This guide applies to SPDs manufactured to be connected to 50 or 60 Hz ac power circuits rated at 100-1000 V RMS. The effects of the presence and operation of SPDs on the quality of power available to the connected loads are described. The interaction between multiple SPDs on the same circuit is also described.