What defines a class of nominal system voltages greater than 1000 volts but less than 100,000 volts?

The classification of electrical systems based on voltage levels is important for ensuring safety, efficiency, and regulatory compliance. In this context, a class of nominal system voltages greater than 1000 volts but less than 100,000 volts is defined as medium voltage.

Medium voltage typically encompasses voltages that are suitable for the distribution of electricity over reasonably short distances, often used in commercial and industrial applications to supply power to transformers and other electrical equipment. This classification is significant because it corresponds to specific standards and practices for installation, operation, and safety.

The definitions of the other voltage classifications do not align with the specified range. Low voltage refers to systems under 1000 volts, high voltage generally includes systems from 100,000 volts and above, and extra high voltage exceeds typical high voltage ranges. Thus, the correct classification for voltages within the range specified in the question is medium voltage, as it accurately describes the operational characteristics and safety considerations for these voltage levels.