1. NFPA Circuits & Pathwaysby
Dan Horon
Cadgraphics Incorporated
RescueLogic.com

2. History
In the 2007 Edition, the Style Tables had become outdated. They were prescriptive, and prevented new technologies. Understanding them required a fire alarm engineer.
NFPA 72, 2007 Edition

3. History
Even though they were less complex than previous Editions, different tables represented types of circuits.
NFPA 72, 2007 Edition

4. History
Even though they were less complex than previous Editions, different tables represented types of circuits.
NFPA 72, 2007 Edition

5. History
Throughout the years that Style Tables were in Code, the older terms Class A and Class B never went away.
Everyone working in fire alarm knew Class B as being a single supervised circuit, and that Class A has an additional redundant path.
NFPA 72, 2007 Edition

6. History
In the 2010 Edition, we worked to replace the tables with simple, easy to understand language. Basically, fire alarm tradition: 1) requires a system to monitor itself for integrity; and 2) recommends -- but not requires -- redundant paths.
NFPA 72, 2010 Edition

7. History
In the 2010 Edition, Class B is described in basic terms.
NFPA 72, 2010 Edition

8. History
In the 2010 Edition, simple performance-based language also describes circuits that had never fit as Class A or B, even though they had been commonplace in fire alarm systems.
NFPA 72, 2010 Edition

9. History
Class 7, the most fault-tolerant, but also most expensive type of circuit is now called Class X. Isolator modules are added to prevent a short-circuit from affecting equipment.
NFPA 72, 2010 Edition

10. History NFPA 72 Annex, 2010 Edition
The Annex of the 2010 Edition explains the pathway Classes, and gives examples. More dramatically, it explains that a single ground fault does not need to be reported if it does not affect the circuit.
NFPA 72 Annex, 2010 Edition

11. Current
Then, in the 2013 Edition, we added back the prescriptive requirement to report a single ground.
NFPA 72, 2013 Edition

12. Current
Wireless or fiber-optic Ethernet does not match up with Class B because two restrictions prevent good network design used for any other type of critically important network.
NFPA 72, 2013 Edition

13. Current
If wireless or fiber paths are installed without redundant pathways, they comply with Class B today.
NFPA 72, 2013 Edition

14. Approved Fire Alarm Pathway
One familiar type of Class B pathway has wires with direct current, and a resistor at the last device. The end-of-line resistor offers a level of assurance that the all wires are connected to the intended device.
(+)
End-of-Line
Resistor
(-)
(+)
End-of-Line
Resistor
(-)
FACP
Version Dan Horon © Permission required for distribution.

15. Approved Fire Alarm Pathway
If a short occurs at any point on a Class B notification appliance pathway, the entire circuit becomes inoperable. X
(+)
End-of-Line
Resistor
(-)
(+)
End-of-Line
Resistor
(-)
FACP
Version Dan Horon © Permission required for distribution.

16. Approved Fire Alarm Pathway
If an open occurs at any point on a Class B initiating device circuit, every device thereafter is inoperable. This is true even when a smoke detector is removed for maintenance.
(+)
End-of-Line
Resistor
(-)
(+)
End-of-Line
Resistor
(-)
FACP
Version Dan Horon © Permission required for distribution.

17. Approved Fire Alarm Pathway
Class B pathways report a single ground connection because, a second ground may connection occur at some point later, and act like a short-circuit. On a Class B IDC, a short-circuit means alarm!
(+)
End-of-Line
Resistor
(-)
(+)
End-of-Line
Resistor
(-)
FACP
Wire touching ground
Version Dan Horon © Permission required for distribution.

18. Approved Fire Alarm Pathway
Class B pathways report a single ground connection because, a second ground connection may occur at some point later, and act like a short-circuit. On a Class B IDC, a short-circuit means alarm!
(+)
End-of-Line
Resistor
(-)
(+)
End-of-Line
Resistor
(-)
FACP
Two wires touching ground
Version Dan Horon © Permission required for distribution.

19. Approved Fire Alarm Pathway
Class B pathways report a single ground connection because, a second ground connection may occur at some point later, and act like a short-circuit. And, on a Class B IDC, a short-circuit means alarm!
(+)
End-of-Line
Resistor
(-)
(+)
End-of-Line
Resistor
(-)
FACP
Two wires touching ground
Version Dan Horon © Permission required for distribution.

20. Approved Fire Alarm Pathway
Up to this point, we’ve seen the required methods of monitoring wires. We don’t know if any device is actually functional, but we can be reasonably certain the intended wires are connected.
(+)
End-of-Line
Resistor
(-)
(+)
End-of-Line
Resistor
(-)
FACP
Version Dan Horon © Permission required for distribution.

21. Approved Fire Alarm Pathway
The Class B, multi-drop signaling line circuit gives each device a numerical address, and the control unit can communicate with all attached devices on just two wires in parallel.
(+)
End-of-Line
Resistor
(-)
(+)
End-of-Line
Resistor
Multi-drop
Communications
001
002
003
004
(-)
FACP
101
Version Dan Horon © Permission required for distribution.

22. Approved Fire Alarm Pathway
An open on a Class B multi-drop SLC reports a trouble if the control unit cannot communicate with every device.
(+)
End-of-Line
Resistor
(-)
(+)
003
004
Multi-drop
Communications
001
002
(-)
FACP X
101
Version Dan Horon © Permission required for distribution.

23. Approved Fire Alarm Pathway
For decades, smart systems have been sold as an improvement over conventional fire alarm systems. AHJs can see the obvious improvement that communication with each device provides.
Yet, minimum Code requirements do not require operational capability of each device to be known. We only require the wires to be monitored.
(+)
End-of-Line
Resistor
(-)
(+)
Multi-drop
Communications
001
002
003
004
(-)
FACP
101
Version Dan Horon © Permission required for distribution.

24. Approved Fire Alarm Pathway
Shorting the two wires at any point stops communication with every device. Not an indication of alarm as with an IDC, a short on the Class B multi-drop SLC reports a trouble.
(+)
End-of-Line
Resistor
(-)
(+)
Multi-drop
Communications
(-)
001
002
003
004
FACP X
101
Version Dan Horon © Permission required for distribution.

25. Approved Fire Alarm Pathway
While every device is attached to the same two wires, a single ground reports a trouble. But, the single ground is not allowed to impact communications.
(+)
End-of-Line
Resistor
(-)
(+)
Multi-drop
Communications
001
002
003
004
(-)
FACP
101
Version Dan Horon © Permission required for distribution.

26. Approved Fire Alarm Pathway
A second ground on a Class B, multi-drop signaling line circuit stops all communication, as it is a short-circuit.
(+)
End-of-Line
Resistor
(-)
(+)
Multi-drop
Communications
(-)
001
002
003
004
FACP
Version Dan Horon © Permission required for distribution.

27. Traditional Fire Alarm
Comparison 1
Every single connection on an Ethernet network is required by IEEE 802 (an ANSI standard) to be galvanically isolated.
Traditional Fire Alarm
Cat 5/6 Ethernet
Report a single ground
A single ground must report even if it has no impact on communication. Wireless or fiber optic paths are excepted because they cannot be grounded, but IEEE 802 isolation means nothing.
A ground has no impact on IEEE 802 equipment. Every connection is galvanically isolated, which prevents propagation of transients, shorts, and grounds. (IEEE 802 is a verifiable ANSI Standard that can be referenced in Code.)

28. Traditional Fire Alarm
Comparison 2
Class A and X paths have exactly two paths that will work if the other fails. A mesh network usually has more than two paths, not knowing exactly where a failure might occur.
Traditional Fire Alarm
Cat 5/6 Ethernet
Redundant paths
Redundant paths do not exist unless they are separately monitored for integrity.
We must know the status of opens, grounds, and shorts on every connected wire.
A mesh network design remains operational even after segments fail. Critical paths have redundancy, and failures of essential equipment report to responsible personnel.

29. Traditional Fire Alarm
Comparison 3
Buildings are increasingly dependent on the network infrastructure.
Traditional Fire Alarm
Cat 5/6 Ethernet
Building networks
No fire alarm equipment should ever be connected to a building network infrastructure. Building networks are not as reliable as traditional fire alarm systems.
 Building networks are a new infrastructure. Modern building systems have standardized on LANs, WANs, and VLANs to interconnect intelligent equipment. A pair of parallel wires connected to multiple addresses is inherently unreliable.

30. Traditional Fire Alarm
Comparison 4
Minimum Code requirements do not require the operational capability of endpoints to be supervised.
Traditional Fire Alarm
Cat 5/6 Ethernet
Device / Endpoint Supervision
Supervising the wiring is enough assurance that a system will operate as intended. SLCs are nice, with each device being addressed, but to require endpoint operation is beyond the scope of the Code.
All endpoints are intelligent, and report improper operation as well as signal path problems. Loss of communication is critical.

31. Traditional Fire Alarm
Wiring Comparison
Every single connection on an Ethernet network is required by IEEE 802 (an ANSI standard) to be galvanically isolated.
Wiring
Traditional Fire Alarm
Cat 5/6 Ethernet
Terminations
Wire nuts, junction boxes, stripped wires, screw terminals
Encased cables, RJ45 ends
Length
Wire length is only limited when voltage drop and capacitance prove communication failure.
Segmented every 300 feet or less. Packets are refreshed by forwarding equipment.
Paralleled
The same wires touch every device in parallel. Like an old party-line telephone system, all devices talk on the same wires.
Multi-layer design. Each device is an individually addressable endpoint. Devices are not physically wired in parallel with each other.
Version Dan Horon © Permission required for distribution.

32. Proposed Fire Alarm Pathway
Network equipment can be thought of in two basic categories: Data Endpoints and Data Forwarding Equipment.
Data Endpoint
Data Forwarding
Data Endpoints
Version Dan Horon © Permission required for distribution.

33. Category 5 Ethernet Cable
In between Data Endpoints and Data Forwarding Equipment, a standardized cable is used. ‘Cat 5’ is an example. 8 7 6 5 4 3 2 1
Transmit Data
Receive Data 8 7 6 5 4 3 2 1
Data Forwarding
Network hub or switch that forwards data to endpoints
Transmit Data +
Data Endpoint
generates or acts on alarm events
Transmit Data -
Receive Data + NC NC
Receive Data - NC
IEEE requires
galvanic isolation on each pair of wires NC
IEEE requires
galvanic isolation on each pair of wires
Version Dan Horon © Permission required for distribution.

34. Category 5 Ethernet Cable
Each Cat 5 cable is galvanically isolated at each end, inside the equipment. The isolation helps prevents transient grounds and shorts on one cable from affecting other components.
IEEE requires
galvanic isolation on each pair of wires 8 7 6 5 4 3 2 1
Transmit Data
Receive Data
IEEE requires
galvanic isolation on each pair of wires
Data Forwarding
Network hub or switch that forwards data to endpoints
Transmit Data + 8 7 6 5 4 3 2 1
Data Endpoint
generates or acts on alarm events
Transmit Data -
Receive Data + NC NC
Receive Data - NC NC
Cat 5 Cable
Four wires are used for data transmission
Data Endpoint
generates or acts on alarm events
Data Forwarding
Network hub or switch that forwards data to endpoints
Version Dan Horon © Permission required for distribution.

35. Category 5 Ethernet Cable
If Transmit Data (+) and (–) or Receive Data (+) and (-) are shorted together, communication stops. In fire alarm systems, a fault condition must be reported within 200 seconds. 8 7 6 5 4 3 2 1
Transmit Data
Receive Data X 8 7 6 5 4 3 2 1
Transmit Data +
Transmit Data -
Receive Data + NC NC
Receive Data - NC
IEEE requires
galvanic isolation on each pair of wires NC
IEEE requires
galvanic isolation on each pair of wires
Data Endpoint
generates or acts on alarm events
Data Forwarding
Network hub or switch that forwards data to endpoints
Version Dan Horon © Permission required for distribution.

36. Category 5 Ethernet Cable
A ground connection on any one signal wire does not block communication. IEEE requires isolation at each end of every Cat 5 cable. Every data packet is checked for errors and re-transmitted until verified. 8 7 6 5 4 3 2 1
Transmit Data
Receive Data 8 7 6 5 4 3 2 1
Transmit Data +
Transmit Data -
Receive Data + NC NC
Receive Data - NC
IEEE requires
galvanic isolation on each pair of wires NC
IEEE requires
galvanic isolation on each pair of wires
Data Endpoint
generates or acts on alarm events
Data Forwarding
Network hub or switch that forwards data to endpoints
Version Dan Horon © Permission required for distribution.

37. Category 5 Ethernet Cable
A second ground connection, on the other wire of a matched pair, will impair communication if it causes a short. A fault condition must be reported within 200 seconds. 8 7 6 5 4 3 2 1
Transmit Data
Receive Data 8 7 6 5 4 3 2 1
Transmit Data +
Transmit Data -
Receive Data + NC NC
Receive Data - NC
IEEE requires
galvanic isolation on each pair of wires NC
IEEE requires
galvanic isolation on each pair of wires
Data Endpoint
generates or acts on alarm events
Data Forwarding
Network hub or switch that forwards data to endpoints
Version Dan Horon © Permission required for distribution.

38. Category 5 Ethernet Cable
Again, each Cat 5 cable is galvanically isolated. Grounds and shorts have no direct path of electrical connection to other equipment or devices. 8 7 6 5 4 3 2 1
Transmit Data
Receive Data
IEEE requires
galvanic isolation on each pair of wires 8 7 6 5 4 3 2 1
IEEE requires
galvanic isolation on each pair of wires
Transmit Data +
Transmit Data -
Receive Data +
Receive Data - NC
Data Endpoint
generates or acts on alarm events
Data Forwarding
Network hub or switch that forwards data to endpoints
Version Dan Horon © Permission required for distribution.

39. Category 5 Ethernet Cable
Proposed Fire Alarm Network
Category 5 Ethernet Cable
Again, each Cat 5 cable is galvanically isolated. Grounds and shorts have no direct path of electrical connection to other equipment or devices. 8 7 6 5 4 3 2 1
Transmit Data
Receive Data
IEEE requires
galvanic isolation on each pair of wires 8 7 6 5 4 3 2 1
IEEE requires
galvanic isolation on each pair of wires
Transmit Data +
Transmit Data -
Receive Data +
Receive Data - NC
Data Endpoints
Data Endpoint
generates or acts on alarm events
Data Forwarding
Network hub or switch that forwards data to endpoints
Version Dan Horon © Permission required for distribution.

40. Proposed Fire Alarm Network
Here you can see a potential vulnerability. If a single path were to become impaired, multiple data endpoints would not communicate with essential equipment.
Good network design prevents a fault on any single cable from making more than one device inoperable.
Data Endpoint
Data Forwarding
Data Endpoints
Version Dan Horon © Permission required for distribution.

41. Proposed Fire Alarm Network
A proposed Class N path would require alternate communication pathways whenever more than one device would be impacted by a fault.
Data Endpoint
Data Forwarding Equipment
Data Endpoints
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42. Class N
Ethernet cables do not report grounds. Therefore, to allow Ethernet network wiring in the Code:
Any segment of a path that affects more than one device must be the equivalent of Class X.
Equivalent of Class B paths may be used when only one device is dependent on the path.