Hotel Guest-Room Retrofit: 520 Hz Sounders on Existing Voice Circuits
A 14-story, 240-room hotel is renovating 60 guest rooms on floors 6–8. The existing addressable FACP has a 25 V voice evacuation system; corridor speakers and guest-room speakers are on the same amplifier. The amplifier has a rated capacity of 120 W and currently carries 85 W. The contractor proposes to replace the in-room speakers with listed 520 Hz low-frequency sounders rated 2 W each, tapping 60 new appliances onto the existing speaker circuits. The longest circuit is 310 ft of 16 AWG, and the contractor says the existing 10 Ah batteries and 1.5 A charger will be fine because the sounders are “only 2 W.” The hotel is fully sprinklered. LAFD plan check has not yet seen the revised drawings. The owner wants to keep the corridors operational during construction and asks whether the sleeping-room devices can be connected to the existing amplifier without other changes.
1. Does the renovation trigger low-frequency (520 Hz) notification in the guest rooms, and what should the designer do before connecting the new sounders?
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Start with the adopted code, not the contractor's assumption. NFPA 72 requires 520 Hz low-frequency notification in sleeping areas for new fire alarm systems, and the LAMC/CBC adoption makes that enforceable through LAFD plan check. A 60-room guest-room renovation that replaces the in-room notification appliances is not just cosmetic; the designer should request a written LAFD interpretation if there is any doubt. Do not rely on the building being sprinklered - sprinkler protection does not waive sleeping-area notification. Even if 520 Hz is not required, the replacement appliances must be listed, synchronized with the corridor system, and audible at the pillow. Before tapping existing circuits, verify amplifier capacity, circuit voltage drop, tap settings, synchronization compatibility, and battery capacity. The existing 25 V amplifier and speaker circuits were not designed for 60 additional 2 W appliances. Submit a code analysis with the permit set.
2. Evaluate the amplifier and circuit capacity. The contractor proposes 60 sounders at 2 W on a 120 W amplifier that already carries 85 W. The longest circuit is 310 ft of 16 AWG. What is the engineering conclusion?
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Do the arithmetic first: 60 × 2 W = 120 W of new load. 85 W existing + 120 W = 205 W, which is 171% of the 120 W amplifier rating. The proposal cannot be approved as a single-amplifier design; a second amplifier or distributed remote power supplies are needed. Then check circuits. If all 60 appliances were on one 25 V circuit, current would be 120 W / 25 V = 4.8 A. A 310 ft one-way 16 AWG circuit has about 620 ft of conductor; 16 AWG is about 4.0 Ω/1,000 ft, so about 2.5 Ω. At 4.8 A the drop would be about 12 V, far beyond the 10% guideline. Even split into six circuits of 10 sounders, each draws 0.8 A and drops about 2 V (8%), marginal after tap tolerances. Recalculate per actual circuit, use larger conductors or remote amplifiers, and verify each appliance's minimum operating voltage. The battery calculation must use the new alarm load, not the old annual-test result.
3. What should the revised submittal include for LAFD approval?
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A complete revision, not a mark-up. Include: (1) a code analysis explaining the 520 Hz determination; (2) a revised riser showing the new amplifiers or power supplies, speaker circuits, and synchronization; (3) amplifier load calculations and per-circuit voltage-drop calculations; (4) battery calculations for 24-hour standby and 5-minute alarm with aging and charger margin; (5) product data sheets and listing information for the 520 Hz appliances; (6) audibility calculations or measurements for guest rooms and corridors; (7) a sequence of operations showing voice evacuation and partial-system construction phasing; (8) firestopping and pathway details; and (9) the required engineer/designer signature and fire alarm permit application. Identify the corridor system as remaining operational during construction and describe temporary protection. Expect LAFD to reject a submittal that only says “existing amplifier is fine.”