THEATERS AND SIMILAR LOCATIONS

70-565 wireway, the sum of the cross-sectional areas of all contained conductors at any cross section shall not exceed 20 percent of the interior cross-sectional area of the auxiliary gutter or wireway. The thirtyconductor limitation of Sections 362-5 and 374-5 shall not apply. 520-6. Enclosing and Guarding Live Parts. Live parts shall be enclosed or guarded to prevent accidental contact by persons and objects. All switches shall be of the externally operable type. Dimmers, including rheostats, shall be placed in cases or cabinets that enclose all live parts. 520-7. Emergency Systems. Control of emergency systems shall comply with Article 700, Emergency Systems. 520-8. Branch Circuits. A branch circuit of any size supplying one or more receptacles shall be permitted to supply stage set lighting. The voltage rating of the receptacles shall not be less than the circuit voltage. Receptacle ampere ratings and branch-circuit conductor ampacity shall not be less than the branch-circuit overcurrent device ampere rating. Table 210-21(b)(2) shall not apply. B. Fixed Stage Switchboard 520-21. Dead Front. Stage switchboards shall be of the dead-front type and shall comply with Part C of Article 384 unless approved based on suitability as a stage switchboard as determined by a qualified testing laboratory and recognized test standards and principles. 520-22. Guarding Back of Switchboard. Stage switchboards having exposed live parts on the back of such boards shall be enclosed by the building walls, wire mesh grills, or by other approved methods. The entrance to this enclosure shall be by means of a self-closing door. 520-23. Control and Overcurrent Protection of Receptacle Circuits. Means shall be provided at a stage lighting switchboard to which load circuits are connected for overcurrent protection of stage lighting branch circuits, including branch circuits supplying stage and auditorium receptacles used for cord- and plug-connected stage equipment. Where the stage switchboard contains dimmers to control nonstage lighting, the locating of the overcurrent protective devices for these branch circuits at the stage switchboard shall be permitted. 520-24. Metal Hood. A stage switchboard that is not completely enclosed dead-front and dead-rear or recessed into a wall shall be provided with a metal hood extending the full length of the board to protect all equipment on the board from falling objects. 520-25. Dimmers. Dimmers shall comply with (a) through (d) below. (a) Disconnection and Overcurrent Protection. Where dimmers are installed in ungrounded conductors, each dimmer shall have overcurrent protection not greater than 125 percent of the dimmer rating, and shall be 70-566 NATIONAL ELECTRICAL CODE disconnected from all ungrounded conductors when the master or individual switch or circuit breaker supplying such dimmer is in the open position. (b) Resistance- or Reactor-type Dimmers. Resistance- or series reactortype dimmers shall be permitted to be placed in either the grounded or the ungrounded conductor of the circuit. Where designed to open either the supply circuit to the dimmer or the circuit controlled by it, the dimmer shall then comply with Section 380-1. Resistance- or reactor-type dimmers placed in the grounded neutral conductor of the circuit shall not open the circuit. (c) Autotransformer-type Dimmers. The circuit supplying an autotransformer-type dimmer shall not exceed 150 volts between conductors. The grounded conductor shall be common to the input and output circuits. (d) Solid-State-type Dimmers. The circuit supplying a solid-state dimmer shall not exceed 150 volts between conductors unless the dimmer is specifically approved for higher voltage operation. Where a grounded conductor supplies a dimmer, it shall be common to the input and output circuits. Dimmer chassis shall be connected to the equipment grounding conductor. (FPN): See Section 210-9 for circuits derived from autotransformers. 520-26. Type of Switchboard. Stage switchboard shall be either one or a combination of the following types: (a) Manual. Dimmers and switches are operated by handles mechanically linked to the control devices. (b) Remotely Controlled. Devices are operated electrically from a pilottype control console or panel. Pilot control panels shall either be part of the switchboard or shall be permitted to be at another location. (c) Intermediate. A stage switchboard with circuit interconnections is a secondary switchboard (patch panel) or panelboard remote to the primary stage switchboard. It shall contain overcurrent protection. Where the required branch circuit overcurrent protection is provided in the dimmer panel, it shall be permitted to be omitted from the intermediate switchboard. 520-27. Stage Switchboard Feeders. Feeders supplying stage switchboards shall be one of the following: (a) Single Feeder. A single feeder disconnected by a single disconnect device. The neutral of feeders supplying solid-state, 3-phase, 4-wire dimming systems shall be considered a current-carrying conductor. (b) Multiple Feeders to Intermediate Stage Switchboard (Patch Panel). Multiple feeders of unlimited quantity shall be permitted, provided that all multiple feeders are part of a single system. Where combined, neutral conductors in a given raceway shall be of sufficient ampacity to carry the maximum unbalanced current supplied by multiple feeder conductors in the same raceway, but need not be greater than the ampacity of the neutral supplying the primary stage switchboard. Parallel neutral conductors shall comply with Section 310-4. The neutral of feeders supplying solidstate, 3-phase, 4-wire dimming systems shall be considered a currentcarrying conductor. ARTICLE 520 - THEATERS AND SIMILAR LOCATIONS 70-567 (c) Separate Feeders to Single Primary Stage Switchboard (Dimmer Bank). Installations with separate feeders to a single primary stage switchboard shall have a disconnecting means for each feeder. The primary stage switchboard shall have a permanent and obvious label stating the number and location of disconnecting means. If the disconnecting means are located in more than one distribution switchboard, the primary stage switchboard shall be provided with barriers to correspond with these multiple locations. The neutral of feeders supplying solid-state, 3-phase, 4-wire dimming systems shall be considered a current-carrying conductor. For purposes of computing supply capacity to switchboards, it shall be permissible to consider the maximum load that the switchboard is intended to control in a given installation, provided that all feeders supplying the switchboard shall be protected by an overcurrent device with a rating not greater than the ampacity of the feeder, and that the opening of the overcurrent device does not have any effect on the egress or emergency lighting systems. (FPN): For computation of stage switchboard feeder loads, see Section 220-10. C. Stage Equipment-Fixed 520-41. Circuit Loads. Footlights, border lights, and proscenium side lights shall be so arranged that no branch circuit supplying such equipment will carry a load exceeding 20 amperes. Exception: Where heavy-duty lampholders only are used, such circuits shall be permitted to comply with Article 210 for circuits supplying heavyduty lampholders. 520-42. Conductor Insulation. Foot, border, proscenium, or portable strip light fixtures and connector strips shall be wired with conductors having insulation suitable for the temperature at which the conductors will be operated, but not less than 125°C (257°F). The ampacity of the 125°C (257°F) conductors shall be that of 60°C (140°F) conductors. All drops from connector strips shall be 90°C (194°F) wire with no more than 6 inches (152 mm) of conductor extending into the connector strip. Article 310, Note 8(a), Notes to Ampacity Tables of 0 to 2000 Volts, shall not apply. (FPN): See Table 310-13 for conductor types. 520-43. Footlights. (a) Metal Trough Construction. Where metal trough construction is employed for footlights, the trough containing the circuit conductors shall be made of sheet metal not lighter than No. 20 MSG treated to prevent oxidation. Lampholder terminals shall be kept at least ½ inch (12.7 mm) from the metal of the trough. The circuit conductors shall be soldered to the lampholder terminals. (b) Other-than-Metal-Trough Construction. Where the metal trough construction specified in Section 520-43(a) is not used, footlights shall consist of individual outlets with lampholders wired with rigid metal conduit, intermediate metal conduit, or flexible metal conduit, Type MC cable, or mineral-insulated, metal-sheathed cable. The circuit conductors shall be soldered to the lampholder terminals. 70-568 NATIONAL ELECTRICAL CODE (c) Disappearing Footlights. Disappearing footlights shall be so arranged that the current supply will be automatically disconnected when the footlights are replaced in the storage recesses designed for them. 520-44. Borders and Proscenium Sidelights. (a) General. Borders and proscenium sidelights shall be (1) constructed as specified in Section 520-43; (2) suitably stayed and supported; and (3) so designed that the flanges of the reflectors or other adequate guards will protect the lamps from mechanical damage and from accidental contact with scenery or other combustible material. (b) Cables for Border Lights. Cables for supply to border lights shall be listed for extra-hard usage. The cables shall be suitably supported. Such cables shall be employed only where flexible conductors are necessary. Ampacity of the conductors shall be as provided in Section 400-5. Exception: Listed multiconductor extra-hard usage type cords not in direct contact with equipment containing heat-producing elements shall be permitted to have their ampacity determined by Table 520-44. Maximum load current in any conductor shall not exceed the values in Table 520-44. Table 520-44. Allowable Ampacity of Listed Extra-Hard Usage Cords with Temperature Ratings of 75°C (167°F) and 90°C (194°F)* [Based on Ambient Temperature of 30°C (86°F)] Size Temperature Rating of Cord Maximum Rating of Over- AWG 75° (167°F) 90°C (194°F) current Device 14 24 28 15 12 32 35 20 10 41 47 25 8 57 65 35 6 77 87 45 4 101 114 60 2 133 152 80 *Ampacity shown is the allowable ampacity for multiconductor cords where only three copper conductors are current-carrying. If the number of current-carrying conductors in a cord exceeds three and the load diversity factor is a minimum of 50 percent, the allowable ampacity of each conductor shall be reduced as shown in the following table. Percent of Number of Allowable Conductors Ampacity 4 thru 6 80 7 thru 24 70 25 thru 42 60 43 and above 50 Note: Ultimate Insulation Temperature. In no case shall conductors be associated together in such a way with respect to the kind of circuit, the wiring method used, or the number of conductors such that the temperature limit of the conductors will be exceeded. ARTICLE 520 - THEATERS AND SIMILAR LOCATIONS 70-569 520-45. Receptacles. Receptacles for electrical equipment or fixtures on stages shall be rated in amperes. Conductors supplying receptacles shall be in accordance with Articles 310 and 400. 520-46. Connector Strips, Drop Boxes, and Stage Pockets. Receptacles for the connection of portable stage lighting equipment shall be pendant or mounted in suitable pockets or enclosures and comply with Section 520-45. Supply cables for connector strips and drop boxes shall be as specified in