Fire Alarm NAC Voltage Drop

[UGAFIREGUY]

I am using the AFAA voltage drop calculator which performs three calculations (Point to Point, End of line & Load centering) Does anyone know if NFPA 72 (2010) states the voltage drop of a NAC cannot exceed 10%

 

[gadfly56]

I am using the AFAA voltage drop calculator which performs three calculations (Point to Point, End of line & Load centering) Does anyone know if NFPA 72 (2010) states the voltage drop of a NAC cannot exceed 10%

There is no such requirement. It is usually up to the designer. I typically see calculations starting out with the batteries derated by 20% so that starting voltage is 20.4 VDC. System Sensor's SpectrAlert series of devices, for example, is listed for operation at 16 to 33 VDC on non-sync circuits, and 17 to 33 on synced circuits. Starting from a derated 20.4 volts, you could tolerate a 16.67% voltage drop on a synced NAC output for these devices.

 

[UGAFIREGUY]

There is no such requirement. It is usually up to the designer. I typically see calculations starting out with the batteries derated by 20% so that starting voltage is 20.4 VDC. System Sensor's SpectrAlert series of devices, for example, is listed for operation at 16 to 33 VDC on non-sync circuits, and 17 to 33 on synced circuits. Starting from a derated 20.4 volts, you could tolerate a 16.67% voltage drop on a synced NAC output for these devices.

Thanks for your input