Notification Appliances and Circuits
Domain 4 covers audible and visible notification, circuit classes, and the voltage-drop checks that keep appliances operating. The exam asks you to apply performance rules, not just identify a horn or strobe.
Core rules
- Public-mode audible appliances must produce 15 dBA above average ambient or 5 dBA above maximum ambient, whichever is greater, measured at 5 ft above the floor.
- Sleeping areas require 75 dBA at the pillow and 15 dBA above ambient.
- Visible appliances are selected from the NFPA 72 candela table based on room dimensions and mounting height; higher candela is required in sleeping areas.
- Visible appliances in the same view must be synchronized.
- Class B notification appliance circuits are supervised with an end-of-line resistor; Class A circuits return to the panel and survive a single open.
- Verify voltage drop so the last appliance receives at least its listed minimum operating voltage.
Worked example
A corridor has an average ambient of 55 dBA and a maximum ambient of 68 dBA. Fifteen above average is 70 dBA; five above maximum is 73 dBA. The greater value, 73 dBA, governs. Measure at 5 ft above the floor and confirm the appliance is listed to produce that output at the expected voltage.
Traps
- Using only 15 dBA above ambient when the maximum ambient is higher.
- Forgetting the 75 dBA pillow requirement in sleeping rooms.
- Mixing synchronized and unsynchronized strobes in one view.
- Ignoring voltage drop on a long Class B circuit.