Which term is used to describe operation at loads that can vary widely over time?

The term that describes operation at loads that can vary widely over time is "Duty, Varying." This terminology is used in electrical systems to indicate that the load is not constant and can fluctuate significantly depending on various factors, such as operational requirements or external conditions.

In practical terms, "Duty, Varying" applies to scenarios where equipment or circuits experience a range of load conditions, making it essential for engineers and electricians to consider the varying nature of these loads when designing and selecting electrical equipment. This understanding helps ensure that the systems can handle the extreme conditions without failure or performance issues.

Other terms listed, such as "Duty, Continuous," refer to loads that remain steady and unchanging, which does not reflect the variable nature described in the question. Similarly, "Duty, Intermittent" refers to loads that are applied and removed periodically, while "Duty, Short-Time" typically applies to loads meant for brief, high-capacity operations. All these definitions highlight specific operational scenarios that do not encapsulate the concept of widely varying loads as effectively as "Duty, Varying."