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HI Fire Alarm: Notification Appliances and Circuits

HI Fire Alarm · Work through your exam, one topic at a time.

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Notification Appliances and Circuits

The Notification Appliances and Circuits domain tests audibility, intelligibility, strobe coverage, and whether the notification appliance circuit can actually deliver voltage to the last device. Calculation items are common.

Audibility and intelligibility

  • Public mode: 65 dBA minimum, or 15 dBA above the average ambient, whichever is greater, and 5 dBA above the maximum ambient lasting more than 60 seconds.
  • Private mode: 55 dBA, or 10 dBA above ambient.
  • Sleeping areas: 75 dBA at the pillow, with low-frequency (520 Hz) appliances where required.
  • Audibility is measured in the occupied space, commonly about 5 ft above the floor.
  • Sound pressure at the minimum hearing distance must not exceed 110 dBA.
  • Voice systems must be intelligible; the AHJ accepts a method such as STI or CIS, with STI around 0.45 to 0.50 commonly specified.

Strobes and synchronization

  • Candela is selected from the room-size table using the greater room dimension; a larger room needs higher candela for the same coverage.
  • Appliances in the same field of view must be synchronized to avoid seizure-inducing flash rates.
  • Wall-mounted strobes use the wall-mount candela column, not the ceiling column.

Circuit design

NACs follow Class A/B rules. Voltage drop is computed at the worst case - battery-backed alarm condition, not normal AC.

Worked example

A Class B NAC carries 12 appliances at 0.15 A each on a 250 ft run of 14 AWG stranded copper (3.07 ohms per 1000 ft). The panel supplies 24 V nominal at the terminals. Is it acceptable if appliances are rated 20 V minimum? Reasoning: current = 12 x 0.15 = 1.8 A. Round-trip resistance = 500 ft x 3.07 / 1000 = 1.535 ohms. Drop = 1.8 x 1.535 = 2.76 V. Voltage at the last device = 24 - 2.76 = 21.2 V, above the 20 V minimum, so the circuit passes - but the margin is thin and a lower panel output under battery load could fail it. Always use the panel's published low-battery voltage for the calculation.

Traps that cost marks

  • Forgetting the return path; resistance must be doubled.
  • Calculating at 24 V AC instead of battery-backed worst case.
  • Using ceiling candela for wall-mounted strobes.
  • Omitting synchronization modules on a shared circuit.
  • Meeting dBA at the panel instead of in the occupied space.