Voltage Drop

[jimmac49]

Does NEC have voltage drop limitations for low voltage (24 volt) fire alarms?

 

[John Paul]

After referring the NFPA 72 the minimum voltage for a 24V Fire Alarm appliances is 16V. It refers to the NEC for wiring sizing only. Hum

 

[RICK NAPIER]

2010 NFPA 72 article 10.14.1 requires fire alarm equipment to work with 85% to 110% of listed voltages and 10.14.2.4 requires installations to fall in the manufacturer's voltage requirements. That would mean a maximum voltage drop to 20.4 volts on a 24 volt system.

 

[jimmac49]

Thanks guys!!

 

[jrohe]

2010 NFPA 72 article 10.14.1 requires fire alarm equipment to work with 85% to 110% of listed voltages

For 24 volt fire alarm systems, a vast majority of notification appliance manufacturers have appliances listed to operate as low as 16 volts, exceeding the requirements of NFPA 72-2010 section 10.14.1

and 10.14.2.4 requires installations to fall in the manufacturer's voltage requirements. That would mean a maximum voltage drop to 20.4 volts on a 24 volt system.

Therefore, the voltage on the NAC would be permitted to drop to a minimum of 16 volts before violating the requirements of NFPA 72-2010 section 10.14.2.4, correct?

On a 24 volt system, the 16 volts equates to a 33% voltage drop, but even if the voltage were 16 volts at the appliance, it would fall within the manufacturer's voltage requirements and meet the requirements of NFPA 72-2010 section 10.14.2.4.

When performing voltage drop calculations for NACs, it is also common practice to use 20.4 volts as the starting voltage when the FACP's secondary power source is storage batteries. This is done because batteries lose voltage as they age and the 20.4 starting voltage is to account for a 15% drop in the battery voltage. If the FACP's secondary power source is line voltage AC power (i.e. generator), 24 volts is typically used as the starting point for voltage drop calculations.