Restaurant Addition: Audibility, Voltage Drop, and the Missing Permit
A contractor is adding a 900-square-foot dining room to an existing 2,400-square-foot restaurant. The existing fire alarm system has a 24-volt notification appliance circuit with four horn/strobes rated at 75 dBA at 10 feet. A calculation shows 18.5 volts at the last device with a 20.4-volt panel supply. The new room will have a 70 dBA ambient sound level when the dish machine and HVAC run. The owner wants two additional ceiling-mounted horn/strobes tapped from the nearest device 'because the ceiling is open.' The local authority has not received plans. The owner says the electrical permit can wait until after the final inspection because 'the fire marshal only checks sprinklers.' The new room has a glass wall to the kitchen and a 36-inch-wide exit door with a manual pull station 30 feet away.
1. Evaluate the audibility of the proposed notification appliances and state what must be done to demonstrate compliance.
Read the worked answer
The proposed design is not supported by the facts given. For public mode notification, NFPA 72 requires the alarm signal to be at least 15 dBA above the average ambient sound level, or 5 dBA above ambient where the ambient exceeds 105 dBA, with a minimum sound level. With a 70 dBA ambient in the new dining room, the target is at least 85 dBA in the occupied area. A horn/strobe rated 75 dBA at 10 feet does not by itself prove 85 dBA at the listener's ear, especially after ceiling height, distance, and attenuation are considered.
The contractor should perform a room-by-room audibility calculation or field measurement after installation and adjust appliance quantity, tap settings, or circuit design as needed. The glass wall to the kitchen and the dish machine noise are relevant because sound transmission and masking can vary. The manual pull station 30 feet from the exit is also a likely violation; NFPA 72 generally requires manual fire alarm boxes within 5 feet of the exit doorway opening. The design should be corrected before installation.
2. Is the notification appliance circuit adequate for two added horn/strobes? Show the reasoning a contractor should use.
Read the worked answer
The existing calculation shows 18.5 volts at the last device from a 20.4-volt supply, a drop of about 9.3 percent. That is already close to the limit many designs use, and adding two horn/strobes will increase current and voltage drop further. The contractor cannot simply tap the nearest device without recalculating the circuit.
The correct approach is to obtain the appliance current ratings at the actual settings, calculate the total load and conductor voltage drop for the entire circuit, and compare the result with the panel and appliance operating voltage requirements. If the last device would fall below the minimum operating voltage, the contractor must add a notification appliance circuit extender or power supply, reduce the load, increase conductor size where permitted, or reconfigure the circuit. The calculation should be documented and retained with the installation records. Field-testing after installation is still required because a calculation is not a substitute for verifying actual operation.
3. What permits, plan review, and inspection steps are required, and how should the contractor respond to the owner's instruction to wait?
Read the worked answer
The contractor should not wait. A fire alarm alteration in a restaurant generally requires an electrical permit and whatever fire alarm plan review or registration the local authority and the State Fire Marshal require. The owner's belief that only sprinklers are reviewed is not a safe basis for skipping the process. The contractor should verify the local requirements in writing, submit plans and calculations before installing devices, and schedule inspections at the required stages.
If the contractor proceeds without approval, the work may be rejected, the certificate of occupancy may be delayed, and the contractor may face licensing consequences. The contractor should explain the sequence to the owner: approved plans first, installation second, acceptance testing and inspection third. The contractor should also confirm that the manual pull station location is corrected and that the notification appliances are listed for fire alarm use. A written change order should address the added cost of the power supply or circuit modifications.