Battery calculation for fire alarm system

Notable Changes in NFPA 72 2022 edition from Chapter 7 & 10

Chapter 7: Documentation (Battery Calculation)

How can a contractor know the performance level a circuit is intended to achieve? The 2022 edition will help clarify any potential uncertainty by requiring the design documents to indicate the pathway class and survivability level. Also, the record of completion and record of inspection and testing forms will incorporate minor revisions to reflect the term revision of stored-energy emergency power supply
systems. Bettery Calculation we will show step by step,

Chapter 10: Fundamentals

Also new, the capacity of batteries will require an additional 5% capacity, changing from 20% safety margin to 25% to account for battery degradation over the life of a battery. The installer will be required to label the battery with a replacement date that does not exceed four years from the date of installation. Effective Jan. 1, 2024, any rechargeable batteries used for secondary power will be required to be listed or recognised by a nationally recognised testing laboratory.

For many editions of NFPA 72, an automatic detector has been required at the location of each control unit, notification appliance circuit power extender and supervising station transmitting equipment when the area is not continuously occupied. This has not changed; however, the next edition adds language that permits the detector to be eliminated where a risk analysis shows it is not required and where acceptable to the AHJ.

Have you ever seen nonfunctional equipment installed in buildings? The 2022 edition will require abandoned fire alarm equipment to be removed and be marked “not in service” while it remains installed.

Pathway Class Designation

Class A, B, C, D, E, & X
Survivability

Class A
1.This will include a redundant signal path – If the path is interrupted, the system feeds both ends of the paths so there are now two paths; the original outgoing path which is now cut shorter, and the return path which is now being used as an outgoing path
2.If wires are used, a wire-to-wire short may shut down the whole path
3.Both conventional and addressable systems fit into this
4.Both the IDC (Initiating Device Circuit) and the NAC (Notification Appliance Circuit) fit into this
5.The panel shows a trouble signal when there is a problem

Class B
1.There is no redundant path
2.Any device beyond a break won’t work
3.If wires are used, a wire-to-wire short may shut down the whole path
4.Both conventional addressable systems fit into this
5.Both IDC and NAC fit into this
6.The panel shows a trouble signal when there is a problem

Class C
1.Uses Handshaking (equivalent to an I’m OK signal) to supervise the path
2.Can have more than one pathway
3.The panel shows a trouble signal when there is a problem
Examples: Signals from the fire panel to the monitoring company
1.The use of IP (Internet Protocol), whether it’s local communications or over the Internet
2.The communicators over the telephone lines that are still in use

Class D
1.Fail-Safe operation – If there is a failure, the device that is controlled by the fire alarm system goes into fire mode
2.No trouble shows on the panel
3.This is annoyance supervision – people get annoyed when things don’t work right and they want the system fixed
Example of a device going into fire mode when a wire breaks or a signal is lost:
4.The fire door closes
5.Emergency door locks release
6.The damper closes
7.The fans shut down

Class E
1.These pathways are not supervised at all
2.No trouble signal will be shown on the panel if the path fails

Class N

This is basically local Ethernet, Token Ring, or other network or IP infrastructure. Unless a single device is connected, or the path is short (less than 20 feet) and really protected in something like conduit, two pathways are used
1.These pathways are verified through end to end communication, like data handshaking
2.Loss of communication between end points on any path show a trouble signal on the panel
3.Problems with one pathway won’t affect the other pathway

Class X
1.This will include a redundant signal path. Like Class A, if the path is interrupted, the system feeds both ends of the circuit so there are two circuits, the original outgoing path which is now cut shorter, and the return path which is now being used as an outgoing path
2.Devices on both sides of an open will continue to communicate with the panel
3.If wires are used, devices on both sides of a wire-to-wire short will continue to communicate with the panel (basically the short has to be isolated on both sides of the short)
4.The panel shows a trouble signal when there is a problem

Survivability

The level of survivability required is dependent on the type of fire alarm system being installed. A higher level of survivability applies to systems used for relocation or partial evacuation of occupants.
Levels of Survivability are 1 – 3, depending on if the wiring is within an Evacuation Signaling Zone (ESZ) or not
An ESZ is a discrete area of a building, bounded by smoke or fir barriers in which occupants are intended to relocate or evacuate.
Level 0 means no survivability is required (wiring within the ESZ)
Level 1 – 3 indicate that attack by fire shall not impair the control and operation of Notification Appliances outside the ESZ
The Key Concept behind Levels 1 -3 is the Fact that Metal Raceway only protects wiring against Mechanical Damage, NOT Damage by Fire.
Level 1, In buildings that are protected by an Automatic Sprinkler System and who’s wiring is installed in Metal Raceways
Level 2 can be accomplished by,
▪ A, 2-hour rated CI Wire OR
▪ B, Fire rated cable system 2-hour OR
▪ C, Fire rated enclosure 2-hour OR
▪ D, Performance alternative approved by the AHJ
Level 3, a combination of Levels 1 & 2.
When attack by fire will affect signaling and control outside of the ESZ, then pathway survivability Levels 2 – 3 are used (at the discretion of the AHJ)
When the wiring outside of the ESZ is necessary for the operation and control of Notification Appliances until it enters the ESZ, Level 2 – 3 must be used
CI rated Cables may be used where pathway survivability Level 2 – 3 is required.
CI Cables are not required for Levels 0 – 1.
Follow NEC 760 and the AHJ’s guidance