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Supervision of Wire Loops in the Fire Alarm System

By Douglas Krantz

Because the Fire alarm system (FAS) is a Life Safety System (people’s lives depend on the fire alarm system working in an emergency), using supervision, the panel makes sure the field devices are always connected to the loop. However, supervision isn't just the panel turning on its yellow light and sounding its local buzzer. When trouble occurs on the system, supervision is the owner doing something about the trouble.


To make sure the wiring is supervised, the wires are installed in the form of loops, according to strict standards, designed specifically for fire alarm systems.

Fire Alarm Loop = Pair of Wires

In a fire alarm system, a loop is a pair of wires. It carries power and signals between the circuit boards inside the fire alarm control panel (FACP) and the off-panel devices in the field.

The loop:

  • As a Power or Control Circuit, carries signals or power to specific fire safety controls and devices

  • IDC (Initiating Line Circuit)

    The IDC is a pair of wires without T-taps, connecting the panel to the input sensing devices.

    Fire Sensing Input Devices (Alarm)

    There is no limit to the number of pull stations and heat detectors you can add to a conventional fire alarm panel because the NO contacts draw no current/power.

    Mixing IDCs and NACs with different manufacturer’s Panel

    Heat detectors and pull stations are usually just normally open, dry contact devices that close when they activate. If this is the case, there is no U.L. compatibility requirement, and you can use anyone’s device on any panel’s IDC (Initiating Device Circuit) that accepts normally open NO contact inputs.

    Dry Contact

    Non-Fire Input Sensing Devices (Supervising other systems)

    No more than 20-supervisory devices per zone. No more than 22,500 square feet ft2 per zone.

    To avoid signal confusion, Fire Sensing (Alarm) and Non-Fire Sensing (Supervisory) devices are not mixed on the same IDC loop.

    The panel supervises the fire alarm wiring using an end-of-line resistor. This resistor allows small electrical current to pass through the wires of the loop, making sure the wires and connections are always complete. For a Class B loop, the end-of-line resistor may be in a distant part of the building, or for a Class A loop, the end-of-line resistor is part of the circuitry of the panel.

    Digital Alarm Communicator Transmitter (DACT)

    Connects to central monitoring station (CMS) which then calls the fire department using a POTS (Plain Old Telephone Service) copper lines connected to a PSTN (Public Switched Telephone Network) with an RJ31X disconnect outlet. 4/2 SIA or contact ID encoding. Macurco Aerionics

    NAC (Notification Appliance Circuit)

    Wired similar to the Initiating Device Circuit (IDC) Class A or Class B loop, the NAC carries power to operate the "Notification Appliances":

    Fire alarm device will have a FWR (Full Wave Rectified) and DC current draw rating. Multi-candela strobe devices will have a different current rating for the different candela settings. The AHJ may require worst case design/installation. The minimum circuit voltage rating of the NAC (typically 85% of nominal 24v or 20.4 volts, but refer to panel’s manual for correct value)

    If both the panel and device are U.L. listed as Regulated, then they are considered compatible, and may not be on the compatibility sheet.

    In the Supervision state (no alarm), a low power electrical current is passed through the entire circuit and either goes back to the panel (Class A) or goes through an end-of-line resistor (Class B). The voltage polarity is reversed. No current flows through the notification appliances because of the diode.

    In alarm state, the DC voltage on the loop is forward biased; the electrical current provided by the panel goes through the notification appliances.

    Edwards Signals (a UTC subsidiary) EST edwards-signals.com/files/Fire_Alarm_FAQs_v2.pdf

    When the fire panel goes into alarm, the panel stops supervising the loop and changes the voltage polarity to normal. Electrical current then goes through the devices, causing the devices to notify the occupants of the building.


    Ancillary connections or Fire Safety functions (ANSI A17.1 National Elevator Code elevator recall, fan shutdown, stadium theater lighting turn on)

    Door hold opens have a permanent magnet. The fire alarm control unit provides 10 mA at 24VDC to create a magnetic field to cancel the permanent magnet. The spring door-closer operates.

    Fire Protection (FP) Wiring


    ANSI A17.1 is the national elevator code, but local codes may be different. You should always refer to the proper codes for your area for exact requirements. Typically you will need the following:

    SLC (Signaling Line Circuit)

    The Signaling Line Circuit (SLC) carries signals both to and from the panel; it uses data to carry the signals out from the panel to field devices, and data to carry the signals back from the field devices to the panel.

    The SLC also provides a small amount of power to operate the field devices.

    Field Devices Connected to an SLC

    It is a long-standing requirement that the fire alarm control unit and system must be operational for it to be legal to use a public building. A fire marshall can have a principal of a school arrested if they have a FACP problem and don't begin a Fire Watch, walking the facility every hour, and notify the fire department.
    KNOX-BOX Rapid Entry System for Fire|EMS|LEO to access property - used for gates and Apartment buildings. 3501 switch is small.
    Strobe Handbook

    Addressable Fire-Alarm Control Panel (FACP)

    To supervise the SLC and to make sure all devices are always connected, the panel sends data to each input or output device, polling the device and asking "are you there"? The device then responds with answers by returning data to the panel saying "I am here."

    With the constant polling of the field devices, the need to supervise the wiring itself isn't necessary; the "Class B" SLC may be T-tapped. Addressable technology also brings the advantages of T-Tap wiring to a fire alarm system’s output notification appliance component. T-Tapping can save the installer 30% or more in labor and materials. Addressable sensors and notification appliances can be "dead-ended".

    As well as the polling of the devices, Class A SLC loops are not T-tapped and are still supervised for wiring issues. Non-addressable appliances require a labyrinth of wires, which take a long time to install and leave many opportunities for errors during installation.

    International Code Council (ICC)/ANSI A117.1 (2009): Accessible and Usable Buildings and Facilities
    roel.ro/oldsite/engtehnice.htm Don't put detectors within 4-inches of a corner or ceiling and no more than 12" below ceiling.
    • 	 Model
    •  Building Code

    Siemens Building Solutions FireFinder XLS System

    Siemens HLIM Isolated Loop Circuit Protectors (ICLP)

    NFPA 72 National Fire Alarm and Signaling Code (NFAC)

    In the 2007 edition, you are no longer given a choice of Styles for Initiating Device Circuits (IDCs), Notification Appliance Circuits (NACs) and the Class B Signaling Line Circuit (SLC).
    Now, the IDCs and NACs are simply designated as either Class A or Class B. Period.

    This alone dropped 16 Style designations from the three tables. The only choice of Styles remaining is for the Class A Signaling Line Circuit which will be designated as either Style 6 or Style 7. The difference being

    In 2007 class/style tables were rooted in “copper” wiring methods. 2010 and 2013 updates reflect fiber (no ground faults, shorts, or lightning vulnerability), Ethernet and wireless sensor networks (WSN) digital data radio modem RF comms [WirelessHART | ISA100.11a]

    Chapter 12 and 24 Survivability

    Level 0 or Level 1 survivability designation. Generally speaking, contractors will use pathway survivability of Level 2 or 3 for in-building fire emergency
    1. Level 0 pathways have no required survivability. With electronic redundancy through various LAN and WAN networks, Ethernet is a good example of Level 0.
    2. Pathway Survivability Level 1 consist of pathways in buildings that are fully protected by an automatic sprinkler system in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems, with any interconnecting conductors, cables, or other physical pathways installed in metal raceways. 2-hour fire-rated circuit integrity (CI) cable or similar.
    3. Rather than just pathway of circuit, entire building is fully protected by a sprinkler system.

    NFPA 13, Standard for the Installation of Sprinkler Systems

    , with any interconnecting conductors, cables or other physical pathways installed in metal raceways.

    UL 2075, Standard for Gas and Vapor Detectors and Sensors. e.g. Carbon Monoxide (CO) sensors.

    SDM Access Control, Panels

    HART - Highway Addressable Remote Transducer

    remote control telemetry: bi-directional industrial field communication protocol between intelligent field instruments and host systems.
    1. Industrial Automation Leaders Fire Alarms First
      1. Siemens AG
      2. Honeywell (Notifier SWIFT wireless mesh & ONYX panels)
      3. UTC Climate, Controls & Security (CCS includes Kidde, Edwards/EST) in addition to BIM, Carrier HVAC/R, & Otis elevators
      4. Tyco
      5. Bosch
      6. ABB (ASEA Brown Boveri), acquired Thomas & Betts in 2012
      7. Schneider Electric SA France
      8. Emerson Industrial Climate Technologies Retail Solutions HVAC, refrigeration, energy monitoring
      9. Rockwell Automation Allen-Bradley
      10. Yokogawa
      11. Omron
      12. Invensys
      13. Mitsubishi Electric
      14. General Electric (GE)
      15. Johnson Controls
      16. Aspen Tech
      17. Moxa
      18. Koyo
      19. Triconex
      • Hubble
      • Cooper
      • Pass & Seymour
      • Simplex TrueAlert addressable fire alarm NACs, IDCs & SLCs
      • DITEK Total Surge Solution (TSS)
      • Manufacturing Execution Systems (MES), Laboratory Information Management System (LIMS), Warehouse Management System (WMS)
      • CERT
    http://books.powerdesigninc.us/external/temporary_power/# Gulf Coast Electrician $2B of projects
    Smart Dispatch is delaying, deferring and bundling work orders

    As hardware has become more capable at lower prices market share shifts towards software and services

    24 VAC “C” wire from HVAC system

    Class II power limited 50 VA


    NFPA 1 Fire Code

    NFPA 101-2015 Life Safety Code: occupancy classification, egress, sprinklers, alarms, emergency lighting, smoke barriers, carbon monoxide (CO) and special hazard protection in both new and existing structures. Calculate occupant load. NICET Level III.

    NFPA 170

    Fire Protection Handbook

    Fire Alarm Signaling Systems


    reedconstructiondata.com/building-codes now http://www.constructconnect.com/building-codes/?search=Virginia

    • OSHA 1910.164 (Fire Detection Systems)
    • OSHA 1910.165 (Employee Alarm Systems)

    ANSUL & AMEREX manufacture kitchen grease fire suppression wet chemical systems including dual agent.

    ANSUL R-101 (dry chemical) & Ansul X R-102 (wet chemical with foam blanket)

    Fusible link melts. Compressed gas

    Salamander - food station

    Proximity hoods are designed for grease and heat laden effluent (Type I Hood) and are shorter in height and depth than a canopy hood. The name "Proximity" or "Backshelf" refers to the close location of the hood with respect to the cooking equipment.

    Exhaust and supply fans

    Dry, chemical or gaseous fire suppression systems - Carbon Dioxide CO2, FM200 Halon,

    Interlocked dry pipe systems - requires a fusible link to melt the sprinkler head AND electronic detection of fire or smoke in the space which in turn opens a valve upstream of the sprinkler head letting water flow into the system.

    A wet sprinkler system is filled with water, with a sprinkler head going off immediately.

    Laboratory exhaust systems need to remain in operation to remove toxic products of combustion. This differs from office type ventilation systems that are configured to shut down in the event of a fire.

    International Association of Property and Evidence IAPE.org recommends the dry chemical in Data Centers, Server/IT rooms, MDF rooms, MRI equipment, Telecom Rooms, Chemical Labs, Electrical Cabinets, Vehicles, Record Storage, Test Chambers, Utility Vaults, Evidence Labs/Storage, CNC Machines, Grinders, Server Cabinets, Flammable Material Storage and Museums

    Inspection, Testing and Maintenance (ITM)

    Fire alarms require initial and periodic ITM

    International Society of Automation <ISA.org>

    WirelessHART & ISA100 Wireless both use 16 channels in unlicensed 2.4 GHz band defined by IEEE 802.15.4 Low-Rate wireless Personal Area Networks (LR-PAN) using star or peer-to-peer mesh topologies.

    National Institute for Certification in Engineering Technologies (NICET)

    NICET is a division of the National Society of Professional Engineers. Jules NICET # 207182
      Fire Alarm Systems (FAS) Certification Standard Model/CBT Application PearsonVUE testing.
    1. > 3 months of technical experience with fire detection and signaling systems $210, 75 questions, 110 min Study Test
    2. > 2-years $270
    3. > 5-years $325
    4. > 10-years $375, 105 questions
    Related experience = low voltage systems, building electrical power or control systems, special hazards systems, or smoke control systems in the role/function of installation, inspection, testing, commissioning, maintenance, technical system estimating and sales, plans preparation, code compliance review, project management, or technical business management.

    licensed fire protection engineer

    NICET Application Applied: NICET ID:


    Society of Fire Protection Engineers,
    Fire Protection Engineering PE Exam Online Prep Course
    Class A vs Class B IDC wiring
      Signal Precedence
    1. Normal - sees EOLR
    2. Alarm - short or smoke/fire, presence of fire danger
    3. Supervisory - off normal condition, monitoring for integrity
    4. Trouble - open circuit, wire cut, problem with equipment

    NFPA 70 NEC Article 700 Power or Control Circuit

    The control circuit, usually from an on-board relay in the panel, turns on or off devices and systems.

    The on-board relays can also be used as part of another panel’s IDC loop, sending alarm, supervisory, and control signals to that other panel. This is particularly useful when the fire alarm panel itself doesn't have an on-board communicator, to provide for off-site monitoring.

    The actual wiring may be a little different from the standard IDC, NAC, and SLC loops, but the control loops still have to be supervised for integrity.

    Some of the uses for the on-board relays:


    Fire Alarm Supervision

    All wiring outside in a fire alarm system, whether it’s an IDC, NAC, SLC, Power or Control loop, needs to be supervised, and supervision includes the call for service and repair of the system, once the panel indicates trouble with the system. An analog system may drift and create a maintenance rather than trouble alert.

    Renovation, Refurbishment, Remediation, Demolition

    Ground Faults

    Non-linear Insulation Resistance (IR) may require more voltage than a VOM/DMM outputs normally to detect and isolate. 80% of electrical maintenance and testing involves evaluating insulation integrity especially in harsh installation environments: temperature extremes, chemical contamination and rubbing/chafing. Megger. Insulation (dielectric) can be compromised by high-voltage. Protected premise alarm systems must identify open circuits and ground faults within 200-seconds.

    Dedicated fans in lieu of environmental fans for smoke control are preferred particularly for elevator and stair shaft pressurization and atriums.


    HART is a widely used communication standard for field devices. The HART-Standard expands the analog 4- bis 20-mA signal into a modulated, industry-standard digital HART signal. Device Descriptions (DD) are written using the Device Description Language (DDL) defined in the HART Specifications and referred to in IEC 61804-2

    Analog signals drift over time, requiring maintenance to adjust sensitivity or drift. Must be tested after a year following installation then every other year. If stable then every 5-years.,

    The advantage is the combination of field-tested analog measured-value transmission and simultaneous digital communication with bi-directional, acyclic transmission, making it possible to transfer diagnostic, maintenance and process information from field devices to higher-level systems. Standardized sets of parameters can be used for cross-vendor operation of all HART devices.

    HART Device Descriptions(EED) are used to integrate HART devices in SIMATIC PDM ensuring easy operation and commissioning of field devices even in hard-to-reach locations.

    Siemens Pyrotronic Cerberus Pro

    Addressable / Intelligent Sensors


    Frontline Test Equipment (FTE) Bluetooth 2.4 GHz ISM protocol analysis "classic" (BR/EDR) to Bluetooth low energy (LE) technology. Teledyne LeCroy located in Charlottesville, VA (434) 984-4500

    NFPA 72-2013 National Fire Alarm and Signaling Code

    Chapter 1 Administration
    1.1 Scope
    1.2 Purpose
    1.3 Application
    1.4 Retroactivity
    1.5 Equivalency
    1.6 Units and Formulas
    1.7 Code Adoption Requirements
    Chapter 2 Referenced Publications
    2.1 General
    2.2 NFPA Publications
    2.3 Other Publications
    2.4 References for Extracts in Mandatory Sections
    Chapter 3 Definitions
    3.1 General
    3.2 NFPA Official Definitions
    3.3 General Definitions
    Chapters 4-6, 8-9, 11, 13, 15-16, 19-20, 22, 25, 28 Reserved
    Chapter 7 Documentation
    7.1 Application
    7.2 Minimum Required Documentation
    7.3 Design (Layout) Documentation
    7.4 Shop Drawings (Installation Documentation)
    7.5 Completion Documentation
    7.6 Inspection, Testing, and Maintenance Documentation
    7.7 Records, Record Retention, and Record Maintenance
    7.8 Forms
    Chapter 10 Fundamentals
    10.1 Application
    10.2 Purpose
    10.3 Equipment
    10.4 Installation and Design
    10.5 Personnel Qualifications
    10.6 Power Supplies
    10.7 Signal Priority
    10.8 Detection and Signaling of Conditions
    10.9 Responses
    10.10 Distinctive Signals
    10.11 ECS Priority Signals
    10.12 Alarm Signals.
    10.13 Fire Alarm Notification Appliance Deactivation
    10.14 Supervisory Signals
    10.15 Trouble Signals
    10.16 Emergency Control Function Status Indicators
    10.17 Notification Appliance Circuits and Control Circuits.
    10.18 Annunciation and Annunciation Zoning
    10.19 Monitoring Integrity of In-Building Fire Emergency Voice/Alarm Communications Systems
    10.20 Documentation and Notification
    10.21 Impairments
    10.22 Unwanted Alarms
    Chapter 12 Circuits and Pathways
    12.1 Application
    12.2 General
    12.3 Pathway Class Designations
    12.4 Pathway Survivability
    12.5 Shared Pathway Designations
    12.6 Monitoring Integrity and Circuit Performance of Installation Conductors and Other Signaling Channels
    12.7 Nomenclature
    Chapter 14 Inspection, Testing, and Maintenance
    14.1 Application
    14.2 General
    14.3 Inspection
    14.4 Testing
    14.5 Maintenance
    14.6 Records
    Chapter 17 Initiating Devices
    17.1 Application
    17.2 Purpose
    17.3 Performance-Based Design
    17.4 General Requirements
    17.5 Requirements for Smoke and Heat Detectors
    17.6 Heat-Sensing Fire Detectors
    17.7 Smoke-Sensing Fire Detectors
    17.8 Radiant Energy–Sensing Fire Detectors
    17.9 Combination, Multi-Criteria, and Multi-Sensor Detectors
    17.10 Gas Detection
    17.11 Other Fire Detectors
    17.12 Sprinkler Waterflow Alarm-Initiating Devices
    17.13 Detection of Operation of Other Automatic Extinguishing Systems
    17.14 Manually Actuated Alarm-Initiating Devices
    17.15 Fire Extinguisher Electronic Monitoring Device
    17.16 Supervisory Signal–Initiating Devices
    Chapter 18 Notification Appliances
    18.1 Application
    18.2 Purpose
    18.3 General
    18.4 Audible Characteristics • Intelligibility: capable of being understood, comprehensible and clear
    18.5 Visible Characteristics — Public Mode
    18.6 Visible Characteristics — Private Mode
    18.7 Supplementary Visible Signaling Method
    18.8 Textual Audible Appliances
    18.9 Textual and Graphical Visible Appliances.
    18.10 Tactile Appliances
    18.11 Standard Emergency Service Interface
    Chapter 21 Emergency Control Function Interfaces
    21.1 Application
    21.2 General
    21.3 Elevator Recall for Fire Fighters' Service
    21.4 Elevator Shutdown
    21.5 Fire Service Access Elevators.
    21.6 Occupant Evacuation Elevators
    21.7 Heating, Ventilating and Air-Conditioning (HVAC) Systems
    21.8 Door and Shutter Release
    21.9 Electrically Locked Doors
    21.10 Exit Marking Audible Notification Systems
    Chapter 23 Protected Premises Fire Alarm Systems
    23.1 Application
    23.2 General
    23.3 System Features
    23.4 System Performance and Integrity
    23.5 Performance of Initiating Device Circuits (IDCs)
    23.6 Performance of Signaling Line Circuits (SLCs)
    23.7 Performance of Notification Appliance Circuits (NACs)
    23.8 System Requirements
    23.9 In-Building Fire Emergency Voice/Alarm Communications
    23.10 Fire Alarm Systems Using Tone
    23.11 Suppression System Actuation
    23.12 Off-Premises Signals
    23.13 Guard’s Tour Supervisory Service
    23.14 Suppressed (Exception Reporting) Signal System
    23.15 Protected Premises Emergency Control Functions.
    23.16 Special Requirements for Low-Power Radio (Wireless) Systems
    Chapter 24 Emergency Communications Systems (ECS)
    24.1 Application
    24.2 Purpose
    24.3 General
    24.4 One-Way Emergency Communications Systems Acoustically Distinguishable Spaces (ADS)
    24.5 Two-Way, In-Building Emergency Communications Systems
    24.6 Information, Command, and Control.
    24.7 Performance-Based Design of Mass Notification Systems
    24.8 Documentation
    Chapter 26 Supervising Station Alarm Systems
    26.1 Application
    26.2 General
    26.3 Central Station Service Alarm Systems.
    26.4 Proprietary Supervising Station Alarm Systems.
    26.5 Remote Supervising Station Alarm Systems
    26.6 Communications Methods for Supervising Station Alarm Systems
    Chapter 27 Public Emergency Alarm Reporting Systems
    27.1 Application
    27.2 General Fundamentals
    27.3 Management and Maintenance
    27.4 Communications Methods
    27.5 Alarm Processing Equipment
    27.6 Alarm Boxes
    27.7 Public Cable Plant
    27.8 Emergency Communications Systems (ECS)
    Chapter 29 Single- and Multiple-Station Alarms and Household Fire Alarm Systems
    29.1 Application
    29.2 Purpose
    29.3 Basic Requirements
    29.4 Assumptions
    29.5 Detection and Notification
    29.6 Power Supplies
    29.7 Equipment Performance
    29.8 Installation
    29.9 Optional Functions
    29.10 Maintenance and Tests
    29.11 Markings and Instructions
    Annex A Explanatory Material
    Annex B Engineering Guide for Automatic Fire Detector Spacing
    Annex C System Performance and Design Guide
    Annex D Speech Intelligibility
    Annex E Sample Ordinance Adopting NFPA 72
    Annex F Wiring Diagrams and Guide for Testing Fire Alarm Circuits
    Annex G Informational References


    Pearson VUE CBT. System layout (plan preparation), system equipment selection, system installation, system acceptance testing, system trouble-shooting, system servicing, and system technical sales.
      Application + Testing Costs Certification Levels
    1. $210
    2. $270
    3. $325
    4. $375
    Exam Code:	10007 - Fire Alarm Systems, Level I
    Applicant’s NICET ID:	207182
    Application Date:	6/18/2016
    Payment Reference:	AU1AE768AAF9
    Total Amount Paid:	$210.00

    The state of Alabama has mandated that electrical contractors can't pull fire alarm (FA) cable or install devices without NICET 2 certification

    Engineering Technologist (Installer) 2-year degree with some math & science vs Engineer (Designer/Planner) with lots of math & science, a 4-year ABET-accredited engineering degree & EIT exam & PE accreditation

    Virginia DPOR ELE classification includes Fire Alarm Systems (FAS) specialty (50 volts or less). PSI’s $85 VA Fire Alarm Systems Contracting FAS specialty exam (with approval from DPOR) allows highlighted & tabbed NEC & NFASC.

      National Fire Protection Association (NFPA)
    1. NFPA 70National Electric Code (NEC)
    2. NFPA 72National Fire Alarm and Signaling Code
    PSI Exams FAS Questions (35/50 to pass)
    Wiring 8
    Grounding 3
    Power Supply 5
    Detectors 12
    Alarm Notification 12
    General Regulations 5
    General Electrical Knowledge 5

    NFPA 72-2010 includes Emergency Communication System (ECS) based on Air Force Civil Engineering Mass Notification Systems (MNS) [Ch 24]
    circuit pathways [Ch 12],
    ECS pathway survivability, ECS secondary power supply and speech intelligibility requirements, far more than just fire hazards --weather alerts and warnings, terrorist attacks, radiological, chemical releases (CBRNE). &mdsash;Biological, Nuclear, Incendiary, Chemical, Explosive (BNICE)

    NFPA 1 “Fire Code

    1. Inspection of permanent and temporary buildings, processes, equipment, systems, and other fire and related life safety situations
    2. Investigation of fires, explosions, hazardous materials incidents, and other related emergency incidents
    3. Review of construction plans, drawings, and specifications for life safety systems, fire protection systems, access, water supplies, processes, hazardous materials, and other fire and life safety issues
    4. Fire and life safety education of fire brigades, employees, responsible parties, and the general public
    5. Existing occupancies and conditions, the design and construction of new buildings, remodeling of existing buildings, and additions to existing buildings
    6. Design, installation, alteration, modification, construction, maintenance, repairs, servicing, and testing of fire protection systems and equipment
    7. Installation, use, storage, and handling of medical gas systems
    8. Access requirements for fire department operations
    9. Hazards from outside fires in vegetation, trash, building debris, and other materials
    10. Regulation and control of special events including, but not limited to, assemblage of people, exhibits, trade shows, amusement parks, haunted houses, outdoor events, and other similar special temporary and permanent occupancies
    11. Interior finish, decorations, furnishings, and other combustibles that contribute to fire spread, fire load, and smoke production
    12. Storage, use, processing, handling, and on-site transportation of flammable and combustible gases, liquids, and solids
    13. Storage, use, processing, handling, and on-site transportation of hazardous materials
    14. Control of emergency operations and scenes
    15. Conditions affecting fire fighter safety
    16. Arrangement, design, construction, and alteration of new and existing means of egress

    Nonpower-Limited Fire Alarm (NPLFA) vs Power-Limited Fire Alarm (PLFA) Circuits"

    Based on NEC's Article 725 Remote-control, Signal, and Power-limited circuits
    1. Class 1 remote-control and signaling circuits typically operate at 120V, but the NEC permits them to operate at up to 600V [725.21(B)]. A wiring method listed in Chapter 3 of the NEC, which includes raceways, cables, and enclosures for splices and terminations [725.25] is required, the same wiring requirements for power and light circuits, but smaller wire sizes than normal power and light circuits are allowed: No. 16 and No. 18 AWG conductors, protected at 10 amperes maximum for No. 16 AWG and 7 amperes maximum for No. 18 AWG.

      Class 1 remote-control circuits are commonly used in motor controllers, bucket control transformers, start/stop stations, signal lights, speed switches, limit switches, elevators, conveyors, and in equipment controlled from one or more remote locations. Class 1 signaling circuits are used in nurses' call systems in hospitals, electric clocks, bank alarm systems, and factory call systems. Class 1 circuits are Non-Power limited, other than by conductor size and over current protection devices (OCPD): 15A for 14 AWG copper, 20A for 12 AWG copper, 30A for 10 AWG copper per 240.4(E) or (G).

      Derating Class 1 Circuit
    2. Class 2 circuits. Due to its power limitations, a Class 2 circuit is considered safe from a fire initiation standpoint and provides acceptable protection from electrical shock. Class 2 circuits typically include wiring for low-energy (100VA or less) for voltages under 30VAC and 60VDC to loads such as low-voltage lighting, HVAC heating/cooling system thermostats, PLCs, security systems, and limited-energy voice, intercom, sound, and public address systems. You can also use them for twisted-pair or coaxial local area networks (LAN) [725.41(A)(4)].

      Class 2 circuits may also protect against electrical fires at higher voltages by limiting the power to 0.5VA | 5mA for circuits between 30V and 150V [Chapter 9, Table 11].

      You can wire Class 2 circuits with Class 2 cable or any of its substitutes permitted by Table 725.61(A), depending on the condition of use.

    3. Class 3 circuits. Use Class 3 circuits when the power demand for circuits over 30V exceeds 0.5VA, but is not more than 100VA [Chapter 9, Table 11]. Class 3 signaling circuits are used in security systems and public address systems; voice, intercom, and sound systems; some nurse call systems, and where a Class 2 circuit is routed a distance where voltage drop becomes a problem.

      Higher levels of voltage and current are permitted for Class 3 circuits (in contrast to Class 2 circuits). To prevent an electric shock hazard, the wiring must be rated no less than 300V [725.71(E) and (F)]. Wiring methods that meet this requirement include PLTC Cable, Class 3 Cable, or any of its permitted substitutions listed in Table 725.61(A), depending on the condition of use.

    Class 2 and 3 systems do not require the same wiring methods as power, light, and Class 1 systems. There are cases when a 2-in. separation is required between these systems.

    725.11(A). When a circuit controls equipment that can introduce a direct life safety hazard the circuit shall be Class 1. Class 2 and Class 3 circuits are not allowed! An example of this is the high limit thermostat switch for a boiler. Another is the high level switch on a tank full of flammable vapors. At a refinery located in Valdez, Alaska the entire process control wiring was done using 24 volt Class 2 and intrinsically safe wiring. However, all the high limits and any other safety device that could possibly introduce a catastrophic failure were wired using Class 1 signaling circuits at 120 volts.

    Wrench symbol 🔧