When must a zone show a trouble indication?

A zone must show a trouble indication when a circuit wire is shorted. A short circuit occurs when there is an unintended path that allows current to flow with little or no resistance. In the context of alarm systems, a short can cause continuous current flow, leading to system malfunctions or failures and preventing accurate zone status reporting.

When a short circuit is present, it indicates a significant issue that must be addressed to ensure the system operates correctly. The trouble indication alerts the user or monitoring personnel that immediate attention is required to maintain the integrity and functionality of the alarm system.

In contrast, while an open circuit or damaged circuit wire can also result in trouble conditions, these specific scenarios may be indicated differently by the system based on its configuration. Additionally, a panel rebooting does not typically trigger a trouble indication related to circuit wiring but rather reflects normal operational processes. Thus, the correct response highlights the importance of addressing shorts to prevent system malfunctions.