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CT Fire Alarm study materials
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CT Fire Alarm: Notification Appliances and Circuits

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

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Notification Appliances and Circuits

Scope

This domain tests audible and visible notification: dBA requirements, candela selection, mounting height, synchronization, NAC loading, voltage drop, and intelligibility for voice systems. Expect questions that combine layout with circuit performance.

Core rules

  • Public-mode audible signals are generally at least 15 dBA above average ambient or 5 dBA above maximum ambient, whichever is greater, with a minimum sound level at the measuring distance. Private-mode requirements differ.
  • Visible appliances are selected by candela rating using the adopted table for room size and ceiling height. Higher ceilings or larger rooms require higher candela; do not reduce candela without justification.
  • Wall-mounted visible appliances are commonly 80–96 in. above the finished floor to the bottom of the appliance, and coordination with sprinkler and other equipment is required.
  • Strobes on the same circuit must be synchronized to avoid effective flash rates outside the permitted range.
  • A NAC must be supervised and must operate all appliances at their minimum rated voltage under low-battery conditions. Account for inrush as well as steady alarm current.

Worked example

A 24 V NAC supplies ten appliances drawing 0.12 A each, for 1.20 A total. The one-way circuit length is 250 ft, so the total conductor length is 500 ft. Using 18 AWG resistance of about 6.51 Ω per 1,000 ft per conductor, resistance is 500 ÷ 1,000 × 6.51 = 3.26 Ω. Voltage drop is 1.20 × 3.26 = 3.91 V. At nominal 24 V, the end of the circuit sees about 20.1 V. At the panel’s low-battery condition, the end voltage is lower still, so compare it with the appliances’ listed minimum-often 16 V-and with panel terminal voltage. If the result is marginal, reduce load, increase conductor size, or split the circuit.

Traps that cost marks

  • Checking only nominal voltage rather than low-battery voltage.
  • Using one-way length in the voltage-drop calculation.
  • Forgetting synchronization when mixing appliances on a NAC.
  • Selecting candela by habit instead of room size and ceiling height.
  • Ignoring inrush current that can overload a NAC at activation.
  • Mounting visible appliances outside the permitted height range.