Notification Appliances and Circuits
This domain tests audible and visible notification design under NFPA 72 Chapter 18. The exam expects you to calculate audibility, select strobe candela from the room size table, synchronize appliances, and recognize when voice intelligibility rather than raw sound pressure is the governing criterion.
Core rules
- Public-mode audible appliances must produce at least 65 dBA at the farthest point or 15 dBA above average ambient, whichever is greater.
- Sleeping areas require 75 dBA at the pillow or 15 dBA above ambient.
- Visible appliances are selected from the candela coverage table: 15 cd for roughly 20 ft × 20 ft, 30 cd for 30 ft × 30 ft, 75 cd for 40 ft × 40 ft, and 110 cd for 50 ft × 50 ft, with adjustments for mounting height.
- Strobes on the same circuit must be synchronized to avoid seizure-risk flash rates.
- Voice systems must be intelligible, not merely loud; speaker placement, tap settings, and echo control matter.
- NACs must be supervised and voltage-drop calculated to the last appliance.
Worked example
A 40 ft × 40 ft room with a 10 ft ceiling needs one wall-mounted strobe. From the table, 75 cd covers 40 ft × 40 ft when mounted in the listed height range. Selecting 15 cd because it is “a small room” fails the coverage table. The reasoning is area coverage, not appliance quantity.
Traps
- Using 65 dBA as the only test and ignoring the 15 dBA-above-ambient rule.
- Selecting candela by habit instead of room dimensions and mounting height.
- Failing to synchronize strobes on separate circuits.
- Designing voice systems by sound pressure only, without intelligibility.
- Forgetting to calculate NAC voltage drop after adding appliances.