What does the overload class rating indicate?

The overload class rating is a critical specification that indicates the maximum duration that an overload relay will allow a motor to operate under a specified overload condition, such as 600% of the full-load current. This rating is essential for protecting motors from damage caused by prolonged overloads, which can lead to overheating and eventual failure.

When a motor experiences a current significantly above its rated capacity, the overload relay is designed to trip and disconnect the motor from the power supply after a certain time has elapsed. The overload class rating defines the time characteristics of this trip; for example, a class 10 rating would typically allow the motor to run for 10 seconds at 600% of its full-load current before tripping.

This concept is distinct from other characteristics, such as the maximum current a motor can handle, which does not consider the timing aspect, or its efficiency, which does not relate directly to overload scenarios. Temperature limits are more related to the thermal protection of the motor rather than overload duration. Thus, the overload class rating directly correlates with the time a motor can sustain a given overload condition before it must be disconnected, making option B the appropriate choice.