AC primary power must be supplied by which of the following?

AC primary power for fire alarm systems must be supplied by a dedicated branch circuit to ensure that the system has a reliable and consistent power source. A dedicated branch circuit is specifically configured to supply power to one particular device or system, which in this case is the fire alarm system. This minimizes the risk of power interruptions or interference from other devices that might share the circuit, ensuring that the fire alarm system remains operational at all times.

Using a dedicated branch circuit also typically complies with various codes and standards governing the installation of fire alarm systems, which mandate that such systems be protected from potential overloads or fluctuations that can occur when multiple devices share the same circuit. This is crucial for maintaining the integrity and reliability of the fire alarm system, especially in emergency situations.

While other options like standard plug outlets, switched power sources, and power strips might seem convenient, they do not provide the necessary level of reliability and code compliance required for crucial safety systems such as fire alarms.