1. Fire Alarm Circuit Design and Fire Alarm Control Units
Chapter 15 1

2. Objectives
List the types of initiating, notification, and signaling line circuits, and discuss the differences
Explain the function of Class A and Class B circuits
Demonstrate understanding of the function of an end-of-line resistor 2

3. Objectives
Compare and contrast the effect of an open conductor, a grounded circuit, and a wire-to-wire short
Explain the function and advantages of an alarm verification feature
Evaluate the differences between hardwired and multiplex fire alarm systems 3

4. Objectives
Draw a riser diagram, a fire alarm system plan view, or a schematic fire alarm system diagram for a system
Calculate the required battery capacity of a fire alarm system
Select a fire alarm circuit based upon predetermined requirements for grounded conductors, wire-to-wire shorts, open conductors, or number of devices on a circuit 4

5. Initiating Device Circuits
Initiating device circuit (IDC): a circuit to which automatic or manual initiating devices are connected to the fire alarm control unit (FACU), where the signal received by the FACU identifies an alarm condition on the circuit but does not identify the specific device actuated
Class B Initiating Device Circuits 5

6. Initiating Device Circuits
Figure Operation of a Class B initiating device circuit (part 1) 6

7. Initiating Device Circuits
Figure Operation of a Class B initiating device circuit (part 2) 7

8. Initiating Device Circuits
Initiating Device Circuit Problems (Faults)
Open conductor: IDC Class B fault that can be caused by a cut or broken wire or a loose terminal
Ground fault: IDC fault that can be caused by a bare wire or terminal in contact with a grounded junction box or some other source of grounding
Wire-to-wire short: two bare wires touch each other, creating an incomplete circuit 8

9. Initiating Device Circuits
Figure Class B circuit fault conditions (part 1) 9

10. Initiating Device Circuits
Figure Class B circuit fault conditions (part 2) 10

11. Initiating Device Circuits
Class A Initiating Device Circuits
Initiating Device Circuit Selection (see Table 15-1, Page 465)
Initiating Device Circuit Alarm Verification Features 11

12. Notification Appliance Circuits
Notification appliance circuits (NACs, see Table 15-2, Page 466): fire alarm circuits to which fire alarm notification appliances are connected
Class B Notification Appliance Circuits
Class A Notification Appliance Circuits 12

13. Signaling Line Circuits
Signaling line circuit (SLC, see Table 15-3, Page 470): a circuit carrying multiple input and output signals of more than one fire alarm system, transmitter, or device
Continuous software interrogation (CSI): microprocessor individually checks status of each device or control unit in sequence, then continuously rechecks devices in order 13

14. Hardwired And Addressable (Multiplex) Fire Alarm Systems
Addressable (multiplex) system: requires a central processing unit (CPU) or a computer and software that specifies and assigns the exact locations or addresses of each initiating device on the fire alarm system 14

15. Fire Alarm Control Units
Fire Alarm Riser Diagram
Fire Alarm System Plan
Schematic Fire Alarm System Diagram
Calculating Fire Alarm Control Unit Battery Capacity 15

16. Fire Alarm Control Units
Figure Fire alarm riser diagram; two wires are shown for each circuit, a Class B system is shown 16

17. Ex. 15-1: Calculation of Battery Capacity17

18. Ex. 15-1: Calculation of Battery Capacity18

19. Ex. 15-1: Calculation of Battery Capacity (cont’d.)19

20. Ex. 15-1: Calculation of Battery Capacity20

21. Ex. 15-1: Calculation of Battery Capacity21

22. Voltage Drop On Notification Appliance Circuits
Standard Operating Voltage for Notification Appliances
Wire Size, Resistance, and Gauge (see Table 15-4, Page 480)
Calculating Voltage Drop in Fire Alarm Wiring 22

23. Voltage Drop On Notification Appliance Circuits23
Figure Illustration of Example 15-2 (follows).

24. Ex. 15-2: Calculation of Voltage Drop24

25. Ex. 15-2: Calculation of Voltage Drop25

26. Ex. 15-2: Calculation of Voltage Drop26

27. Summary
Fire alarm circuits connect initiating devices and notification appliances to the fire alarm control unit that permits the system to meet performance objectives
Circuit logic, styles, and isolation can be chosen to increase the reliability of a fire alarm system 27

28. Summary
Fire alarm control unit (FACU) is the nerve center of a fire alarm system
Can display system logic in riser diagrams, plan views, and schematic diagrams
Battery backup for FACU is calculated by determining power requirements for all components in the alarm 28

29. Summary Calculation of voltage drop in a fire alarm circuit
Important responsibility for a fire alarm system designer
Provides evidence that notification appliances will work in accordance with their listing 29