Most utilities are required to submit reliability performance statistics to their regulators. However, they typically don't provide detailed information on the full range of power quality characteristics that are important to their commercial and industrial customers, including the expected number of voltage sags and interruptions, harmonic distortion levels, voltage unbalance, and voltage variations. The IEEE and the International Electrotechnical Commission (IEC) have developed standards to provide guidance in some of these areas. Other events such as voltage sags, are just starting to receive attention. What do you need to know to make sure your equipment works properly? What levels of power quality can you expect? It's useful to divide power quality considerations into two categories: Steady-state, also called continuous, characteristics and disturbances.