When does the ATS not transfer power back to the normal source immediately?

The automatic transfer switch (ATS) is designed to manage the transition between utility power and backup power sources, like generators. The scenario where power is not transferred back to the normal source immediately occurs during the process of utility stability verification.

When utility power is restored, the ATS will not switch back from generator power to normal utility power until it confirms that the utility supply is stable. This means the voltage and frequency are within acceptable ranges and there are no fluctuations that could jeopardize the safety and reliability of the connected loads. This precaution helps to protect equipment and ensures that the power supply is dependable before resuming normal operation.

In contrast, other scenarios, such as a brownout where normal power fluctuates for a short time, may lead to the ATS temporarily disconnecting power until conditions are deemed stable. Similarly, if the generator is still running or if the load exceeds capacity, these situations would not directly relate to the ATS's decision-making regarding the transfer back to the utility source, as those conditions pertain to power availability or capacity rather than utility stability.