Which of the following factors is essential when selecting overcurrent protection devices for a motor control circuit?

When selecting overcurrent protection devices for a motor control circuit, the rated full-load current of the motor is essential because it directly relates to the amount of current the motor will draw under normal operating conditions. Overcurrent protection devices, such as circuit breakers or fuses, must be rated appropriately to handle this current while providing protection against overloads and short circuits.

The full-load current is calculated based on the motor's specifications, and the chosen protection device must be able to carry this current safely without tripping during normal operation. This ensures that the motor can run efficiently without unnecessary interruptions while still being safeguarded against conditions that could lead to damage or failure, such as overloads from mechanical issues or electrical faults.

Other factors like ambient temperature, the length of the power supply cable, and the frequency of the supply voltage can influence the performance and efficiency of the motor circuit, but they are not the primary determinants in the selection of the overcurrent protection device itself. Instead, they may be considered to ensure appropriate sizing and installation, but the rated full-load current remains the fundamental criterion for selecting the suitable protection level.