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Article 640

Audio Signal Processing, Amplification, and Reproduction Equipment

Part I. General

  1. Scope.
    1. Covered. This article covers equipment and wiring for audio signal generation, recording, processing, amplification, and reproduction; distribution of sound; public address; speech input systems; temporary audio system installations; and electronic organs or other electronic musical instruments. This also includes audio systems subject to Article 517, Part VI, and Articles 518, 520, 525, and 530.Informational Note: Examples of permanently installed distrib‐ uted audio system locations include, but are not limited to, restaurant, hotel, business office, commercial and retail sales environments, churches, and schools. Both portable and perma‐ nently installed equipment locations include, but are not limited to, residences, auditoriums, theaters, stadiums, and movie and television studios. Temporary installations include, but are not limited to, auditoriums, theaters, stadiums (which use both temporary and permanently installed systems), and outdoor events such as fairs, festivals, circuses, public events, and concerts.
    2. Not Covered. This article does not cover the installation and wiring of fire and burglary alarm signaling devices.
  2. Definitions. For purposes of this article, the following definitions apply.Abandoned Audio Distribution Cable. Installed audio distribu‐ tion cable that is not terminated at equipment and not identi‐ fied for future use with a tag.Audio Amplifier or Pre-Amplifier. Electronic equipment that increases the current or voltage, or both, of an audio signal intended for use by another piece of audio equipment. Ampli‐ fier is the term used within this article to denote an audio amplifier.Audio Autotransformer. A transformer with a single winding and multiple taps intended for use with an amplifier loud‐ speaker signal output.Audio Signal Processing Equipment. Electrically operated equipment that produces, processes, or both, electronic signalsthat, when appropriately amplified and reproduced by a loud‐ speaker, produce an acoustic signal within the range of normal human hearing (typically 20–20 kHz). Within this article, the terms equipment and audio equipment are assumed to be equiva‐ lent to audio signal processing equipment.Informational Note: This equipment includes, but is not limited to, loudspeakers; headphones; pre-amplifiers; microphones and their power supplies; mixers; MIDI (musical instrument digital interface) equipment or other digital control systems; equaliz‐ ers, compressors, and other audio signal processing equipment; and audio media recording and playback equipment, including turntables, tape decks and disk players (audio and multimedia), synthesizers, tone generators, and electronic organs. Electronic organs and synthesizers may have integral or separate amplifica‐ tion and loudspeakers. With the exception of amplifier outputs, virtually all such equipment is used to process signals (utilizing analog or digital techniques) that have nonhazardous levels of voltage or current.Audio System. Within this article, the totality of all equipment and interconnecting wiring used to fabricate a fully functional audio signal processing, amplification, and reproduction system.Audio Transformer. A transformer with two or more electri‐ cally isolated windings and multiple taps intended for use with an amplifier loudspeaker signal output.Equipment Rack. A framework for the support, enclosure, or both, of equipment; can be portable or stationary.Informational Note: See EIA/ECIA 310-E-2005, Cabinets, Racks, Panels and Associated Equipment.Loudspeaker. Equipment that converts an ac electric signal into an acoustic signal. The term speaker is commonly used to mean loudspeaker.Maximum Output Power. The maximum power delivered by an amplifier into its rated load as determined under specified test conditions.Informational Note: The maximum output power can exceed the manufacturer’s rated output power for the same amplifier.Mixer. Equipment used to combine and level match a multi‐ plicity of electronic signals, such as from microphones, elec‐ tronic instruments, and recorded audio.Portable Equipment. Equipment fed with portable cords or cables intended to be moved from one place to another.Rated Output Power. The amplifier manufacturer’s stated or marked output power capability into its rated load.Technical Power System. An electrical distribution system with grounding in accordance with 250.146(D), where the equip‐ ment grounding conductor is isolated from the premises grounded conductor and the premises equipment grounding conductor except at a single grounded termination point within a branch-circuit panelboard, at the originating (main breaker) branch-circuit panelboard, or at the premises ground‐ ing electrode.Temporary Equipment. Portable wiring and equipment inten‐ ded for use with events of a transient or temporary nature where all equipment is presumed to be removed at the conclu‐ sion of the event.
  3. Locations and Other Articles. Circuits and equipment shall comply with 640.3(A) through (M), as applicable.
    1. Spread of Fire or Products of Combustion.Section 300.21 shall apply.
    2. Ducts, Plenums, and Other Air-Handling Spaces. Section 300.22(B) shall apply to circuits and equipment installed in ducts specifically fabricated for environmental air. Section 300.22(C) shall apply to circuits and equipment installed in other spaces used for environmental air (plenums).
      Exception No. 1: Class 2 and Class 3 cables installed in accordancewith 725.135(B) and Table 725.154 shall be permitted to be installed in ducts specifically fabricated for environmental air.
      Exception No. 2: Class 2 and Class 3 cables installed in accordancewith 725.135(C) and Table 725.154 shall be permitted to be installed in other spaces used for environmental air (plenums).Informational Note: NFPA 90A -2015, Standard for the Installation of Air-Conditioning and Ventilating Systems, 4.3.10.2.6.5, permits loudspeakers, loudspeaker assemblies, and their accessories listed in accordance with UL 2043-2013, Fire Test for Heat and Visi‐ ble Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces, to be installed in other spaces used for envi‐ ronmental air (ceiling cavity plenums).
    3. Cable Trays. Cable trays and cable tray systems shall be installed in accordance with Article 392.Informational Note: See 725.135(H), 725.136(G), and Table 725.154 for the use of Class 2, Class 3, and Type PLTC cable in cable trays.
    4. Hazardous (Classified) Locations. Equipment used in hazardous (classified) locations shall comply with the applica‐ ble requirements of Chapter 5.
    5. Assembly Occupancies. Equipment used in assembly occupancies shall comply with Article 518.
    6. Theaters, Audience Areas of Motion Picture and Television Studios, and Similar Locations. Equipment used in theaters, audience areas of motion picture and television studios, and similar locations shall comply with Article 520.
    7. Carnivals, Circuses, Fairs, and Similar Events. Equipment used in carnivals, circuses, fairs, and similar events shall comply with Article 525.
    8. Motion Picture and Television Studios. Equipment used in motion picture and television studios shall comply with Arti‐ cle 530.
    9. Swimming Pools, Fountains, and Similar Locations. Audio equipment used in or near swimming pools, fountains, and similar locations shall comply with Article 680.
    10. Combination Systems. Where the authority having juris‐ diction permits audio systems for paging or music, or both, to be combined with fire alarm systems, the wiring shall comply with Article 760.Informational Note: For installation requirements for such combination systems, refer to NFPA 72 -2013, National Fire Alarm and Signaling Code, and NFPA 101-2015, Life Safety Code.
    11. Antennas. Equipment used in audio systems that contain an audio or video tuner and an antenna input shall comply with Article 810. Wiring other than antenna wiring that connects such equipment to other audio equipment shall comply with this article.
    12. Generators. Generators shall be installed in accordance with 445.10 through 445.12, 445.14 through 445.16, and445.18. Grounding of portable and vehicle-mounted genera‐ tors shall be in accordance with 250.34.
    13. Organ Pipes. Additions of pipe organ pipes to an elec‐ tronic organ shall be in accordance with 650.4 through 650.9 .
  4. Protection of Electrical Equipment. Amplifiers, loud‐ speakers, and other equipment shall be so located or protected as to guard against environmental exposure or physical damage, such as might result in fire, shock, or personal hazard.
  5. Access to Electrical Equipment Behind Panels Designed to Allow Access. Access to equipment shall not be denied by an accumulation of wires and cables that prevents removal of panels, including suspended ceiling panels.
  6. Mechanical Execution of Work.•
    1. Installation of Audio Distribution Cables. Cables installedexposed on the surface of ceilings and sidewalls shall be supported in such a manner that the audio distribution cables will not be damaged by normal building use. Such cables shall be secured by straps, staples, cable ties, hangers, or similar fittings designed and installed so as not to damage the cable. The installation shall conform to 300.4 and 300.11(A).
    2. Abandoned Audio Distribution Cables. The accessible portion of abandoned audio distribution cables shall be removed.
    3. Installed Audio Distribution Cable Identified for Future Use.
      1. Cables identified for future use shall be marked with a tag of sufficient durability to withstand the environment involved.
      2. Cable tags shall have the following information:
    1. Date cable was identified for future use
    2. Date of intended use
    3. Information related to the intended future use of cable
  7. Grounding.
    1. General. Wireways and auxiliary gutters shall be connec‐ ted to an equipment grounding conductor(s), to an equipment bonding jumper, or to the grounded conductor where permit‐ ted or required by 250.92(B)(1) or 250.142. Where the wireway or auxiliary gutter does not contain power-supply wires, the equipment grounding conductor shall not be required to be larger than 14 AWG copper or its equivalent. Where the wire‐ way or auxiliary gutter contains power-supply wires, the equip‐ ment grounding conductor shall not be smaller than specified in 250.122.
    2. Separately Derived Systems with 60 Volts to Ground. Grounding of separately derived systems with 60 volts to ground shall be in accordance with 647.6.
    3. Isolated Ground Receptacles. Isolated grounding-type receptacles shall be permitted as described in 250.146(D), and for the implementation of other technical power systems in compliance with Article 250. For separately derived systems with 60 volts to ground, the branch-circuit equipment ground‐ ing conductor shall be terminated as required in 647.6(B).
    Informational Note: See 406.3(D) for grounding-type recepta‐ cles and required identification.
  8. Grouping of Conductors. Insulated conductors of different systems grouped or bundled so as to be in close physi‐ cal contact with each other in the same raceway or other enclo‐ sure, or in portable cords or cables, shall comply with 300.3(C)(1).
  9. Wiring Methods.
    1. Wiring to and Between Audio Equipment.
      1. Power Wiring. Wiring and equipment from source of power to and between devices connected to the premises wiring systems shall comply with the requirements of Chap‐ ters 1 through 4, except as modified by this article.
      2. Separately Derived Power Systems. Separately derived systems shall comply with the applicable articles of this Code, except as modified by this article. Separately derived systems with 60 volts to ground shall be permitted for use in audio system installations as specified in Article 647.
      3. Other Wiring. All wiring not connected to the premises wiring system or to a wiring system separately derived from the premises wiring system shall comply with Article 725.
    2. Auxiliary Power Supply Wiring. Equipment that has a separate input for an auxiliary power supply shall be wired in compliance with Article 725. Battery installation shall be in accordance with Article 480. This section shall not apply to the use of uninterruptible power supply (UPS) equipment, or other sources of supply, that are intended to act as a direct replacement for the primary circuit power source and are connected to the primary circuit input.Informational Note: Refer to NFPA 72 -2013, National Fire Alarm and Signaling Code, where equipment is used for a fire alarm system.
    3. Output Wiring and Listing of Amplifiers. Amplifiers with output circuits carrying audio program signals shall be permit‐ ted to employ Class 1, Class 2, or Class 3 wiring where the amplifier is listed and marked for use with the specific class of wiring method. Such listing shall ensure the energy output is equivalent to the shock and fire risk of the same class as stated in Article 725. Overcurrent protection shall be provided and shall be permitted to be inherent in the amplifier.Audio amplifier output circuits wired using Class 1 wiring methods shall be considered equivalent to Class 1 circuits and shall be installed in accordance with 725.46, where applicable.Audio amplifier output circuits wired using Class 2 or Class 3 wiring methods shall be considered equivalent to Class 2 or Class 3 circuits, respectively. They shall use conductors insula‐ ted at not less than the requirements of 725.179 and shall be installed in accordance with 725.133 and 725.154.Informational Note No. 1: ANSI/UL 1711-2006, Amplifiers for Fire Protective Signaling Systems, contains requirements for the listing of amplifiers used for fire alarm systems in compliance with NFPA 72 -2013, National Fire Alarm and Signaling Code.Informational Note No. 2: Examples of requirements for listing amplifiers used in residential, commercial, and professional use are found in ANSI/UL 813-1996, Commercial Audio Equipment; ANSI/UL 1419-2011, Professional Video and Audio Equipment; ANSI/UL 1492-2010, Audio-Video Products and Accessories; ANSI/ UL 6500-2006, Audio/Video and Musical Instrument Apparatus for Household, Commercial, and Similar Use; and UL 62368-1-2012, Audio/Video, Information and Communication Technology Equipment— Part 1: Safety Requirements.
    4. Use of Audio Transformers and Autotransformers. Audio transformers and autotransformers shall be used only for audio signals in a manner so as not to exceed the manufacturer’s stated input or output voltage, impedance, or power limita‐ tions. The input or output wires of an audio transformer or autotransformer shall be allowed to connect directly to the amplifier or loudspeaker terminals. No electrical terminal or lead shall be required to be grounded or bonded.
  10. Audio Systems Near Bodies of Water. Audio systems near bodies of water, either natural or artificial, shall be subject to the restrictions specified in 640.10(A) and (B).

Exception: This section does not include audio systems intended for use on boats, yachts, or other forms of land or water transportation used near bodies of water, whether or not supplied by branch-circuit power.

Informational Note: See 680.27(A) for installation of underwa‐ ter audio equipment.

  1. Equipment Supplied by Branch-Circuit Power. Audio system equipment supplied by branch-circuit power shall not be placed horizontally within 1.5 m (5 ft) of the inside wall of a pool, spa, hot tub, or fountain, or within 1.5 m (5 ft) of the prevailing or tidal high water mark. The equipment shall be provided with branch-circuit power protected by a ground-fault circuit interrupter where required by other articles.
  2. Equipment Not Supplied by Branch-Circuit Power. Audio system equipment powered by a listed Class 2 power supply or by the output of an amplifier listed as permitting the use of Class 2 wiring shall be restricted in placement only by the manufacturer’s recommendations.

Informational Note: See 640.10(A) for placement of the power supply or amplifier if supplied by branch-circuit power.

Part II. Permanent Audio System Installations

  1. Use of Flexible Cords and Cables.
    1. Between Equipment and Branch-Circuit Power. Power supply cords for audio equipment shall be suitable for the use and shall be permitted to be used where the interchange, main‐ tenance, or repair of such equipment is facilitated through the use of a power-supply cord.
    2. Between Loudspeakers and Amplifiers or Between Loud‐ speakers. Cables used to connect loudspeakers to each other or to an amplifier shall comply with Article 725. Other listed cable types and assemblies, including optional hybrid commu‐ nications, signal, and composite optical fiber cables, shall be permitted.
    3. Between Equipment. Cables used for the distribution of audio signals between equipment shall comply with Article 725. Other listed cable types and assemblies, including optional hybrid communications, signal, and composite optical fiber cables, shall be permitted. Other cable types and assemblies specified by the equipment manufacturer as acceptable for the use shall be permitted in accordance with 110.3(B).
      Informational Note: See 770.3 for the classification of compositeoptical fiber cables.
    4. Between Equipment and Power Supplies Other Than Branch-Circuit Power. The following power supplies, other than branch-circuit power supplies, shall be installed and wired
      between equipment in accordance with the requirements of this Code for the voltage and power delivered:
      1. Storage batteries
      2. Transformers
      3. Transformer rectifiers
      4. Other ac or dc power suppliesInformational Note: For some equipment, these sources such as in items (1) and (2) serve as the only source of power. These could, in turn, be supplied with intermittent or continuous branch-circuit power.
    5. Between Equipment Racks and Premises Wiring System. Flexible cords and cables shall be permitted for the electrical connection of permanently installed equipment racks to the premises wiring system to facilitate access to equipment or for the purpose of isolating the technical power system of the rack from the premises ground. Connection shall be made either by using approved plugs and receptacles or by direct connection within an approved enclosure. Flexible cords and cables shall not be subjected to physical manipulation or abuse while the rack is in use.
  2. Wiring of Equipment Racks and Enclosures. Metal equipment racks and enclosures shall be bonded and groun‐ ded. Bonding shall not be required if the rack is connected to a technical power ground.Wires, cables, structural components, or other equipment shall not be placed in such a manner as to prevent reasonable access to equipment power switches and resettable or replacea‐ ble circuit overcurrent protection devices.Supply cords or cables, if used, shall terminate within the equipment rack enclosure in an identified connector assembly. The supply cords or cable (and connector assembly if used) shall have sufficient ampacity to carry the total load connected to the equipment rack and shall be protected by overcurrent devices.
  3. Conduit or Tubing.
    1. Number of Conductors. The number of conductors permitted in a single conduit or tubing shall not exceed the percentage fill specified in Table 1, Chapter 9.
    2. Nonmetallic Conduit or Tubing and Insulating Bushings. The use of nonmetallic conduit or tubing and insulating bush‐ ings shall be permitted where a technical power system is employed and shall comply with applicable articles.
  4. Wireways, Gutters, and Auxiliary Gutters. The use of metallic and nonmetallic wireways, gutters, and auxiliary gutters shall be permitted for use with audio signal conductors and shall comply with applicable articles with respect to permit‐ ted locations, construction, and fill.
  5. Loudspeaker Installation in Fire Resistance–Rated Partitions, Walls, and Ceilings. Loudspeakers installed in a fire resistance–rated partition, wall, or ceiling shall be listed and labeled, or identified as speaker assemblies for fire resistance, or installed in an enclosure or recess that maintains the fire resistance rating.

Informational Note: Fire-rated construction is the fire-resistive classification used in building codes.

Part III. Portable and Temporary Audio System Installations

  1. Multipole Branch-Circuit Cable Connectors. Multipole branch-circuit cable connectors, male and female, for power- supply cords and cables shall be so constructed that tension on the cord or cable is not transmitted to the connections. The female half shall be attached to the load end of the power supply cord or cable. The connector shall be rated in amperes and designed so that differently rated devices cannot be connected together. Alternating-current multipole connectors shall be polarized and comply with 406.7(A) and (B) and406.10. Alternating-current or direct-current multipole connec‐ tors utilized for connection between loudspeakers and amplifi‐ ers, or between loudspeakers, shall not be compatible with nonlocking 15- or 20-ampere rated connectors intended for branch-circuit power or with connectors rated 250 volts or greater and of either the locking or nonlocking type. Signal cabling not intended for such loudspeaker and amplifier inter‐ connection shall not be permitted to be compatible with multi‐ pole branch-circuit cable connectors of any accepted configuration.Informational Note: See 400.14 for pull at terminals.
  2. Use of Flexible Cords and Cables.
    1. Between Equipment and Branch-Circuit Power. Power supply cords for audio equipment shall be listed and shall be permitted to be used where the interchange, maintenance, or repair of such equipment is facilitated through the use of a power-supply cord.
    2. Between Loudspeakers and Amplifiers, or Between Loud‐ speakers. Installation of flexible cords and cables used to connect loudspeakers to each other or to an amplifier shall comply with Part I of Article 400 and Parts I, II, III, and IV of Article 725, respectively. Cords and cables listed for portable use, either hard or extra-hard usage as defined by Article 400, shall also be permitted. Other listed cable types and assemblies, including optional hybrid communications, signal, and compo‐ site optical fiber cables, shall be permitted.
    3. Between Equipment and/or Between Equipment Racks. Installation of flexible cords and cables used for the distribu‐ tion of audio signals between equipment shall comply with Parts I and II of Article 400 and Parts I, II, and III of Arti‐ cle 725, respectively. Cords and cables listed for portable use, either hard or extra-hard service as defined by Article 400, shall also be permitted. Other listed cable types and assemblies, including optional hybrid communications, signal, and compo‐ site optical fiber cables, shall be permitted.
    4. Between Equipment, Equipment Racks, and Power Supplies Other Than Branch-Circuit Power. Wiring between the following power supplies, other than branch-circuit power supplies, shall be installed, connected, or wired in accordance with the requirements of this Code for the voltage and power required:
      1. Storage batteries
      2. Transformers
      3. Transformer rectifiers
      4. Other ac or dc power supplies
    5. Between Equipment Racks and Branch-Circuit Power. The supply to a portable equipment rack shall be by means of listed extra-hard usage cords or cables, as defined in Table 400.4. For outdoor portable or temporary use, the cords or cables shall be further listed as being suitable for wet loca‐
      tions and sunlight resistant. Sections 520.5, 520.10, and 525.3 shall apply as appropriate when the following conditions exist:
      1. Where equipment racks include audio and lighting and/or power equipment
      2. When using or constructing cable extensions, adapters, and breakout assemblies
  3. Wiring of Equipment Racks. Equipment racks fabrica‐ ted of metal shall be bonded and grounded. Nonmetallic racks with covers (if provided) removed shall not allow access to Class 1, Class 3, or primary circuit power without the removal of covers over terminals or the use of tools.Wires, cables, structural components, or other equipment shall not be placed in such a manner as to prevent reasonable access to equipment power switches and resettable or replacea‐ ble circuit overcurrent protection devices.Wiring that exits the equipment rack for connection to other equipment or to a power supply shall be relieved of strain or otherwise suitably terminated such that a pull on the flexible cord or cable will not increase the risk of damage to the cable or connected equipment such as to cause an unreasonable risk of fire or electric shock.
  4. Environmental Protection of Equipment. Portable equipment not listed for outdoor use shall be permitted only where appropriate protection of such equipment from adverse weather conditions is provided to prevent risk of fire or electric shock. Where the system is intended to remain operable during adverse weather, arrangements shall be made for maintaining operation and ventilation of heat-dissipating equipment.
  5. Protection of Wiring. Where accessible to the public, flexible cords and cables laid or run on the ground or on the floor shall be covered with approved nonconductive mats. Cables and mats shall be arranged so as not to present a trip‐ ping hazard. The cover requirements of 300.5 shall not apply to wiring protected by burial.
  6. Equipment Access. Equipment likely to present a risk of fire, electric shock, or physical injury to the public shall be protected by barriers or supervised by qualified personnel so as to prevent public access.

information technology equipment and information technology equipment areas.

  1. Definitions.Abandoned Supply Circuits and Interconnecting Cables. Instal‐ led supply circuits and interconnecting cables that are not terminated at equipment and not identified for future use with a tag.Critical Operations Data System. An information technology equipment system that requires continuous operation for reasons of public safety, emergency management, national security, or business continuity.•Information Technology Equipment Room. A room within theinformation technology equipment area that contains the information technology equipment. [75:3.3.9]Remote Disconnect Control. An electric device and circuit that controls a disconnecting means through a relay or equivalent device.Zone. A physically identifiable area (such as barriers or separa‐ tion by distance) within an information technology equipment room, with dedicated power and cooling systems for the infor‐ mation technology equipment or systems.
  2. Other Articles. Circuits and equipment shall comply with 645.3(A) through (I), as applicable.
  1. Spread of Fire or Products of Combustion. Sections 300.21, 770.26, 800.26, and 820.26 shall apply to penetrations of the fire-resistant room boundary.
  2. Wiring and Cabling in Other Spaces Used for Environmen‐ tal Air (Plenums). The following sections and tables shall apply to wiring and cabling in other spaces used for environ‐ mental air (plenums) above an information technology equip‐ ment room:

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