Which malfunction would NOT be indicated by an alarm at the telltale panel?

The correct answer is based on understanding the specific functions of the alarm system and what typical malfunctions trigger alarms at the telltale panel.

When considering why overloading of the electrical circuit would not be indicated by an alarm at the telltale panel, it is important to know that the telltale panel primarily monitors and provides alerts for conditions that are directly related to system integrity, functioning, and safety protocols. An overloaded circuit can lead to various issues, such as tripping breakers or potential failure of connected devices, but it typically does not trigger a dedicated alarm. Instead, the system is designed to respond to such conditions internally, often by protective devices that disengage the electrical flow rather than sending a specific alarm signal.

On the other hand, the malfunction scenarios mentioned in other options would generally trigger alarms. For example, the failure of both primary and secondary filaments, improper functioning of the alarm system, and the failure of the backup power supply directly affect the integrity or performance of the alarm system itself. Such failures need immediate attention and would be designed to alert operators at the telltale panel, ensuring they are aware of critical issues that could compromise safety or operational capability.