According to the text, how should circuit breakers be loaded when not specifically marked?

When determining how circuit breakers should be loaded when not specifically marked, the best approach is to refer to the manufacturer's rating. This is because circuit breakers are designed with specific load capacities that vary based on temperature and other factors defined by the manufacturer. Following the manufacturer's rating ensures safe and efficient operation of the breaker, as it takes into account the design limits under normal operating conditions.

In contrast, loading circuit breakers by either column or by ambient temperature alone does not provide the specificity needed to account for the capabilities of the breaker under varying conditions. Loading solely by the 60° C column could lead to overloading in ambient conditions that may not be accounted for, resulting in potential safety hazards or equipment failure. Thus, relying on the manufacturer's rating is the most accurate and safe approach to loading circuit breakers.