Define NAC and SLC in fire alarm systems.

• A. NAC stands for Notification Alarm Channel; SLC stands for Signaling Logical Channel.
• B. NAC powers audible devices; SLC powers lights.
• C. NAC is the network access circuit; SLC is signaling line circuit for data.
• D. NAC is the Notification Appliance Circuit powering audible/visible devices; SLC is the Signaling Line Circuit used by addressable devices to communicate with the panel.

Answer: (D)

In fire alarm systems, two circuit types handle signaling in different ways. The Notification Appliance Circuit powers the audible and visible devices—such as horns and strobe lights—that alert occupants during an alarm. The Signaling Line Circuit is the data path used by addressable devices to communicate with the fire alarm panel, carrying two-way information about device status, events, and addresses. Because addressable devices rely on the SLC to report to the panel, while NACs are dedicated to energizing notification devices, the described definitions—NAC for powering audible/visible devices and SLC for signaling line communication with the panel—are the correct concepts.