FDAS | Power Suppy Options

 

The Power supply is the source of electricity that provides the power needed to operate the Fire Alarm Control Panel and including all devices connected to it.

A fire alarm system serves many functions and the differences between the functions can be a bit confusing, so I created a visual guide to fire alarm basics. A fire alarm system is an important part of the overall fire protection and life safety of a building.

Primary Power
This is the 220Vac power supply voltage from the electrical utility company. Inside the Fire Alarm Control Panel it is then converted to the system voltage of 24Vdc. An engine-driven generator (this is not a standby generator, or a site generator meeting the requirements in NFPA 72), and Stored-Energy Emergency Power Supply System (SEPSS), or a co-generation system.

Secondary Power
In case of power failure of the primary power supply, the batteries (serving as the secondary power supply) automatically switch over to provide uninterrupted power to the system. This include providing an additional power source in addition to the primary power such as emergency generator so there is backup power if primary power is lost or providing power through a single source such as a Stored-Energy Emergency Power Supply System (SEPSS).

It is important for a fire alarm system to be provided with a reliable power so it can operate during an emergency. There are options to met this when it comes to choosing a reliable power supply, as well as some calculations that are necessary to ensure that the fire alarm system is provided with sufficient backup power.

Batteries are the most popular option to provide a secondary power supply, the most common type of battery is a Valve-Regulated Lead-Acid battery and they are typically located within the fire alarm control unit enclosure, or in a separate battery box located near the fire alarm control unit. Batteries need to be sized so that they can provide power to the entire fire alarm system for 24 hours in standby and 5 minutes in alarm, if the system has an emergency voice alarm communication system (EVACS), then the batteries need to provide capacity for 15 minutes in alarm in addition to the 24 hours in standby. The additional time is required to allow for a longer evacuation time as buildings with an EVACS typically utilize a partial evacuation that would require constant communication with the occupants during the evacuation.

Another option in providing through a secondary power supply  is the use of an emergency generator designed, installed, and maintained in accordance with NFPA 110, Standard for Emergency and Standby Power Systems, which provides power to the fire alarm system through an automatic transfer switch. If using an emergency generator, you are still required to provide batteries as well just in case there is an issue with getting the emergency generator started. These batteries however, only need to provide a capacity for 4 hours instead of the 24 hours in standby. 

And instead of providing two separate power supplies, you are allowed to provide power via a Stored-Energy Emergency Power Supply System (SEPSS) also known as an Energy Storage System (ESS) or an Uninterruptible Power Supply (UPS).  The SEPSS must be configured in accordance with NFPA 111 and provide 24 hours of backup battery. The SEPSS is also fed via a compliant primary power supply such as utility power or an on site generator. 

Battery Calculations
If batteries are part of the secondary power source for a fire alarm system then they must be sized to provide capacity to run the system for 24 hours in standby and then either 5 minutes in alarm or 15 minutes in alarm for EVACS. 


♦ First the total system standby current and the total system alarm current is calculated. This is done by multiplying the standby current and alarm current for each piece of equipment by the total quantity of each piece of equipment and adding them together, the result is the total AMPS required in standby and alarm. Both the standby current and the alarm current for equipment can be found from the manufacturer in the data sheet.

♦ Then total standby capacity is required by multiplying the total system standby current by the required 24 hours to achieve the required standby capacity in AMP-HRS. The same is done with the alarm capacity, however, instead of 24 hours, the current is multiplied by either 5 minutes (0.083 hours) or 15 minutes (.25 hours) to achieve the required alarm capacity in AMP-HRS.

♦ Finally, both the standby capacity and the alarm capacity is added together and a 25% safety factor is applied to arrive at the total required battery capacity.

DragonsDean Enterprise | Speak to a Specialist

Location:Iligan City, Lanao del Norte, Philippines

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