Circuits, Systems, and Control Functions (NFPA 72-2022 Ch. 12, 21, 23, 24, and 26)
NFPA 72-2022 Ch. 12 · NFPA 72-2022 Ch. 21 · NFPA 72-2022 Ch. 23 · NFPA 72-2022 Ch. 24 · NFPA 72-2022 Ch. 26 · NFPA 70-2020 Art. 760 and 770 · Outline tasks 1.1.2, 1.2.2, 1.2.1, 1.1.1, 1.3.1
What NICET expects at Level I
This topic does not ask you to design the system. It asks you to install, test, and repair its circuits knowing what each designation means. You must recognize the pathway classes of Chapter 12, know what the panel shows when a circuit opens, goes to ground, or shorts, locate interface relays and elevator detectors (Ch. 21), understand the special functions of Chapter 23 (PAS, pre-signal, alarm verification), and know the basic supervising station response times (Ch. 26). Many questions are scenarios: "The Class B SLC opened halfway down the run; what do you see at the panel?"
Chapter 12: pathway classes (§12.3)
| Class | What it means | Typical example |
|---|---|---|
| A (§12.3.1) | Redundant path; keeps operating past a single open; a single ground does not stop operation; both are annunciated as trouble | SLC or NAC looped back to the panel |
| B (§12.3.2) | No redundant path; operation stops at the open; keeps operating with a single ground; faults annunciated | IDC/NAC with an end-of-line (EOL) resistor |
| C (§12.3.3) | End-to-end communication is verified; individual conductors are not monitored | IP/cellular communicator to the supervising station |
| D (§12.3.4) | Fail-safe: the fault is not annunciated, but the intended function is performed if the pathway fails | Magnetic door holders |
| E (§12.3.5) | Not monitored for integrity | Circuits exempt from monitoring (§12.6) |
| N (§12.3.6) | Network (Ethernet, PoE, fiber): primary and redundant pathways to each device, verified by end-to-end communication | Networked panels and IP speakers |
| X (§12.3.7) | Like A, but also survives a short circuit and an open combined with a ground | SLC with short-circuit isolators |
Practical key: on a Class A loop without isolators, a short can take out the whole loop; short-circuit tolerance belongs to Class X.
Separate outgoing and return routing (§12.3.8)
For Class A, N, and X, the outgoing and return conductors must be routed separately. §12.3.8.1 allows them in the same cable or raceway only: (1) for up to 10 ft (3 m) where entering or leaving a device, appliance, or control unit enclosure; (2) for single drops to individual devices; (3) within a single room of not more than 1000 ft² (93 m²), for a drop to multiple devices that does not include emergency control function devices. Annex A.12.3.8 recommends at least 12 in. (vertical) and 48 in. (horizontal) of separation.
Pathway survivability (§12.4)
| Level | Requirement |
|---|---|
| 0 (§12.4.1) | No special protection |
| 1 (§12.4.2) | Building fully sprinklered (NFPA 13) + metal raceway or metal armored cable |
| 2 (§12.4.3) | 2-hour CI or fire-resistive cable, 2-hour cable system, 2-hour rated enclosure or protected area, or an AHJ-approved alternative |
| 3 (§12.4.4) | Building fully sprinklered + one of the Level 2 means |
| 4 (§12.4.5, new in 2022) | 1-hour protection (CI cable, cable system, or enclosure rated 1 hour) |
The levels are not a hierarchy (A.12.4): a higher number is not "better." Which level is required is decided by other chapters, for example §24.3.14 for voice systems using partial evacuation. CI cable keeps its rating only if it is installed per its listing and the manufacturer's instructions.
Monitoring for integrity and ground faults (§12.6)
A single open or a single ground fault must be indicated automatically within 200 seconds (§12.6.1). On conventional Class B circuits the EOL must be at the end of the circuit; a T-tap leaves branches unmonitored. §12.6 contains exemptions (for example §12.6.6: a notification appliance in the same room as the control equipment with conductors in raceway). To locate a ground: isolate circuit by circuit, then split the faulted circuit in halves.
Chapter 23: system functions
- Positive alarm sequence (PAS, §23.8.1.2): acknowledgment by trained personnel within 15 s; investigation up to 180 s. A second PAS detector or any other initiating device (manual station) activates everything immediately. Requires AHJ approval.
- Pre-signal (§23.8.1.1): the initial signal sounds only at constantly attended locations; the general alarm requires human action. Requires AHJ approval.
- Alarm verification (§23.8.5.4): smoke detectors only; retard–reset–restart cycle of no more than 60 s; use only where unwanted alarms are anticipated.
- Waterflow = alarm (operation within 90 s, Ch. 17); valve tamper = supervisory.
- Releasing service: before testing, secure the suppression system against discharge (disconnect solenoids/actuators per the manufacturer).
- NAC power extenders: they are system power supplies: they need their own secondary supply (24 h + 5 min for non-voice), their power troubles must be reported to the FACU, and they need smoke detection at their location if the area is not continuously occupied (Ch. 10).
- Partial evacuation (§23.10.2): a fire in one evacuation zone must not prevent notification in the other zones.
Chapter 21: emergency control functions
- Interface relay within 3 ft (1 m) of the controlled component (§21.2.4, 2022 edition). The wiring between the FACU and the relay must be monitored for integrity or be Class D (fail-safe).
- Phase I recall (§21.3): only detectors in the elevator lobby, hoistway, machine room, and control room/space. Designated-level lobby detector → alternate level; other lobbies → designated level; machine room/hoistway → designated (or alternate) level + flashing 'fire hat' in the car. Lobby detector on the ceiling within 21 ft of the centerline of each door.
- Power shutdown (shunt trip, §21.4): heat detectors within 2 ft of each sprinkler, with a lower temperature rating and higher sensitivity; waterflow/pressure switches with no time delay; loss of control-circuit voltage = supervisory.
- HVAC and doors: duct detectors shut down fans per the matrix; door holders release doors; electrically locked egress doors unlock before or at the same time as public-mode notification.
Chapter 24 (basics)
An EVACS sounds an alert tone followed by a voice message; live voice takes priority over automatic messages. Intelligibility is planned by ADS (acoustically distinguishable space).
Chapter 26: supervising stations
| Item | Value / rule |
|---|---|
| Alarm at a central station (§26.3.8) | Retransmit immediately; runner within 2 h if equipment must be reset |
| Supervisory / trouble | Notify immediately; runner 2 h / service personnel 4 h |
| Verification at the station (§26.2) | Must not delay retransmission more than 90 s |
| DACT (§26.6.4) | 1 telephone line + second means (cellular/IP or radio); each channel tested every 6 h or less; 90 s max. per attempt |
| Performance-based (§26.6.3) | Single path: failure annunciated within 60 min; multiple paths: each every 6 h |
Types: central (listed company), proprietary (same owner, own staff), and remote (where central station service is not required).
Common traps: confusing 200 s (trouble for an open/ground) with 90 s (waterflow or supervising station) or 10 s (notification actuation); believing Class A survives a short (that is Class X); thinking Level 4 is the "highest"; treating the annex 12 in./48 in. separation as mandatory; using a newer edition's interface-relay distance (the 2022 answer is 3 ft); putting a time delay on the waterflow switch used for shunt trip.
How to find it fast in the printed code
- Pathway classes and separation: Chapter 12, §12.3 and §12.3.8; survivability: §12.4 and Table A.12.4 (in Annex A, explanatory only); 200 s: §12.6.1. These pages are worth a permanent tab.
- PAS and pre-signal: §23.8.1; alarm verification: §23.8.5.4.
- 3-ft relay: §21.2.4; elevators: §21.3 (recall) and §21.4 (shunt trip). Tab the start of Chapter 21.
- Supervising stations: §26.3.8 (responses), §26.6.3 (IP/cellular), §26.6.4 (DACT).
- Use the index at the back of NFPA 72 with terms such as "Pathway," "Survivability," "Elevators," "Positive alarm sequence," "Pre-signal," and "Digital alarm communicator." Remember that 21.x means Chapter 21, 26.x means Chapter 26, and so on.
Tip: memorize the class pattern (A = survives an open, X = open + short, B = stops at the open) and look up the fine numbers in your tabbed code book.
What to tab in your books
| Section | Why |
|---|---|
| NFPA 72 §12.3 | Pathway classes A, B, C, D, E, N, and X |
| NFPA 72 §12.3.8 / §12.3.8.1 | Separate outgoing and return routing (Class A, N, X); 10 ft, single-drop, and ≤ 1000 ft² room exceptions |
| NFPA 72 A.12.3.8 | Recommended separation 12 in. vertical / 48 in. horizontal (annex) |
| NFPA 72 §12.4 and Table A.12.4 | Survivability levels 0 to 4 (Level 4 new in 2022) |
| NFPA 72 §12.6.1 | Monitoring for integrity: open or ground indicated within 200 s |
| NFPA 72 §12.2.3 | Optical fiber (NEC 770/760/840) and installation per manufacturer's instructions |
| NFPA 72 §21.2.4 | Interface device within 3 ft (1 m) of the controlled component |
| NFPA 72 §21.3 | Elevator Phase I recall: designated level, alternate level, and 'fire hat' |
| NFPA 72 §21.4 | Elevator power shutdown (shunt trip): 2 ft, no time delay, voltage supervision |
| NFPA 72 §23.8.1 | Pre-signal and positive alarm sequence (15 s / 180 s) |
| NFPA 72 §23.8.5.4 | Alarm verification (60 s max.) |
| NFPA 72 §23.10.2 | Partial evacuation: a fire in one zone does not affect other zones |
| NFPA 72 §24.3.14 | Pathway survivability for emergency communications systems |
| NFPA 72 §26.3.8 | Central station responses: alarm, supervisory, trouble (runner 2 h / 4 h) |
| NFPA 72 §26.6.3 | Performance-based technologies (IP/cellular): 60 min / 6 h |
| NFPA 72 §26.6.4 | DACT: second transmission means, channel tests, 90 s per attempt |
| NFPA 72 Ch. 7 (§7.3) | Design documentation: pathway classes and survivability levels |
Chapter vocabulary
- Pathway
- Medium (wire, fiber, radio) that connects system equipment; its performance is designated by class (Ch. 12).
- Signaling line circuit (SLC)
- Circuit that carries multiple input/output (addressable) signals between the FACU and devices.
- Initiating device circuit (IDC)
- Conventional circuit to which initiating devices are connected; normally Class B with an EOL.
- Notification appliance circuit (NAC)
- Circuit that powers horns, strobes, and speakers.
- Redundant path
- Second path that maintains communication if the first one fails (Classes A, N, X).
- Open / ground fault / short circuit
- The three basic wiring faults; the pathway class defines which ones the circuit tolerates.
- Fault isolator
- Device that separates a shorted section so the rest of the SLC keeps operating (Class X).
- End-of-line device (EOL)
- Resistor or other element at the end of a Class B circuit that allows the wiring to be monitored.
- Monitoring for integrity
- Automatic detection of opens and ground faults on conductors, annunciated within 200 s (§12.6.1).
- Pathway survivability
- Ability of a pathway to keep operating during a fire; Levels 0 to 4 (§12.4).
- Circuit integrity (CI) cable
- Cable rated to keep a circuit operating for a period (1 or 2 h) under fire conditions.
- Emergency control function interface device
- Relay or module that connects the FACU to elevators, HVAC, doors, etc.; within 3 ft of the controlled component (§21.2.4).
- Designated level / alternate level
- Floors to which elevators are sent on Phase I recall, depending on which detector operates.
- Visual warning signal ('fire hat')
- Indicator in the elevator car that flashes when a hoistway or machine room detector operates.
- Shunt trip
- Automatic disconnection of elevator main-line power before sprinkler discharge (§21.4).
- Positive alarm sequence (PAS)
- Approved delay: acknowledge within 15 s and investigate up to 180 s before general notification.
- Pre-signal feature
- Initial signal only at attended locations; the general alarm requires human action.
- Alarm verification feature
- Retard–reset–restart cycle (60 s max.) used with smoke detectors.
- Supervisory signal
- Indicates an abnormal condition of a supervised system (for example, a closed valve), not a fire.
- Releasing service
- FACU that actuates a suppression system (clean agent, preaction, etc.).
- NAC power extender
- Remote power supply that powers additional NACs; requires its own secondary supply.
- Central / proprietary / remote supervising station
- Types of stations that receive signals away from the protected premises (Ch. 26).
- DACT
- Digital alarm communicator transmitter: dials the supervising station over a telephone line and requires a second transmission means.
- Performance-based technologies
- IP or cellular communication to the supervising station (§26.6.3).
- Acoustically distinguishable space (ADS)
- Zone or subdivision with its own acoustic characteristics in which voice intelligibility is planned and evaluated.
45 practice questions cover this chapter, each with an explanation and the code section. Get lifetime access or try the free practice exam.
More Level I study guides
- 8-week study plan
- Fundamentals and Definitions
- Initiating Devices
- Notification Appliances
- Circuits, Systems, and Control Functions
- NEC 2020 (NFPA 70): Article 760 and Wiring Methods
- Basic Electricity and Calculations
- Inspection, Testing and Maintenance
- Troubleshooting, Repair and Device Replacement
- Job Site Safety: OSHA 1910/1926 and First Aid
- Technical Documents, Drawings, and Submittals
- Community-Reported Topics
- Level I tabbing guide for your printed code books
- Strategy with printed code books
- Key numbers (NFPA 72 · NEC · OSHA)
- Formulas and conversions
- Fire alarm glossary for the NICET exams