This blog is primarily for FA system designers, installers, AHJs and plan reviewers. If you design, install or review plans for fire alarm systems, this is a must read for you.
NFPA 72, 10.17.1 states that a failure of one notification appliance circuit (NAC) shall not affect the operation of any other NAC. This was approved for Chapter 4 (Now 10) of NFPA 72 in the late 1990s. This was primarily approved to prevent adding a power supply trip to a NA circuit which also controlled appliances. Shortly thereafter a new circuit definition was approved; Control Circuit (CC). A CC was designed to be utilized for tripping and synchronizing notification appliance power supplies. The only difference between a NAC and a CC is that appliances cannot be installed on a CC and therefore is not classified as a NAC and complies with 10.17.1. But, here is the problem. A system designed with an FACU NAC becoming a CC by being utilized to trip a NAC power supply is now the weak link in the notification portion of the system. Should the CC fail, all of the circuits on the NAC(s) will be affected and prevent activation. Although it’s not required by NFPA 72, all CCs should be wired Class A so that an open circuit will not prevent the NA power supply from activating the appliances.
An alternative to this partial solution, as the above does not account for short circuits or multiple ground faults, is to trip the NAC power supply with a control module, wired Class A, on the signaling line circuit (SLC). If this is to be the process, then the SLC should be class A with an isolation module on either side of the relay module. If synchronization of the strobes is required, due to multiple NAPSs in the same area that one NAPS is serving, then getting the sync pulse to the NA power supply will need to be addressed.
Neither of these solutions, partial or not, is required by any code or standard that the writer is aware of, but, as life safety specialists, we should all take reasonable measures to make all premises safe to everyone who enters. Replacing a Class B circuit with a Class A, especially when the NAPS is next to the FACU, is not labor intensive, nor is using a relay module to trip the NAPS. The writer intends to present this for the next NFPA 72 cycle and hopefully this, or some form of this, will be approved and accepted.
