What type of detection system is mentioned to be located at the branch duct-to-common duct connection?

The detection system located at the branch duct-to-common duct connection is typically a fusible link or heat detection device. This is because these devices are designed to respond to changes in temperature that indicate a fire situation.

Fusible links work by melting at predetermined temperatures, which allows for the release of the dry chemical agent to extinguish the fire. The proximity of the detection system to the duct connections is critical, as it can quickly identify the heat produced by a fire in the ductwork, ensuring timely activation of the extinguishing system.

While electronic monitoring systems and thermal imaging devices can be useful for overall fire safety, they do not specifically function in the same capacity or location as fusible links. Smoke detectors generally detect smoke rather than temperature and are not typically placed in duct connections due to the airflow that may dilute smoke and delay detection. Therefore, a fusible link or heat detection device is essential for effective fire detection and response in this specific context.