If secondary power is provided, what must the primary power source be capable of?

The primary power source must be capable of operating under full load with secondary power disconnected. This requirement ensures that the fire alarm system remains functional and reliable even when secondary power systems, such as backup batteries or generators, are not in use. If a primary power source fails to support the system under full load without the assistance of a secondary source, the integrity and reliability of the fire alarm system would be compromised. This capability is crucial for safety, as fire alarm systems must remain operational at all times, especially during emergencies or power outages.

While other options may seem relevant to different systems or scenarios, they do not address the critical requirement of maintaining functionality solely on primary power. For example, independence from secondary power is an important feature, but it doesn’t specify the operational requirements under load. Similarly, manual overrides and handling low voltage requirements pertain to different aspects of fire alarm systems and do not directly relate to the primary power's performance under the specified conditions.