How should a circuit breaker with a 60° C terminal be loaded unless otherwise marked?

Circuit breakers are designed to handle a specific amount of current and are rated based on the temperature of their terminals. The capacity of the breaker can vary significantly based on the temperature rating specified for the terminals. The correct loading for a circuit breaker with a 60° C terminal is by the 60° C column unless specified otherwise.

This is due to the fact that the thermal characteristics of electrical components dictate that their performance at higher temperatures becomes less reliable and can lead to overheating or tripping if they are loaded beyond their rated capacity. The 60° C rating reflects the maximum temperature at which the wire can operate safely without risking damage to the insulation and ensuring the proper function of the circuit.

By using the 60° C column for loading, you are adhering to the manufacturer's specified conditions for safe operation, thereby ensuring that the circuit breaker functions correctly without the risk of failure or tripping due to overheating.