INTRINSICALLY SAFE SYSTEMS

70-499 (FPN): See Section 250-78 for additional bonding requirements in hazardous (classified) locations. (b) Types of Equipment Grounding Conductors. Where flexible conduit is used as permitted in Section 503-3, it shall be installed with internal or external bonding jumpers in parallel with each conduit and complying with Section 250-79. Exception: In Class III, Division 1 and 2 areas, the bonding jumper shall be permitted to be deleted where all the following conditions are met: a. Approved liquidtight flexible metal 6 feet (1.83 m) or less in length, with approved fittings, is used; b. Overcurrent protection in the circuit is limited to 10 amperes or less; c. The load is not a power utilization load. ARTICLE 504 - INTRINSICALLY SAFE SYSTEMS 504-1. Scope. This article covers the installation of intrinsically safe (I.S.) apparatus, wiring, and systems for Class I, II, and III locations. (FPN): For further information, see Installation of Intrinsically Safe Instrument Systems in Class I Hazardous Locations, ANSI/ISA RP 12.6-1987. 504-2. Definitions. For the purpose of this article: Associated Apparatus: Apparatus in which the circuits are not necessarily intrinsically safe themselves, but that affect the energy in the intrinsically safe circuits and are relied upon to maintain intrinsic safety. Associated apparatus may be either: 1. Electrical apparatus that has an alternative type protection for use in the appropriate hazardous (classified) location, or 2. Electrical apparatus not so protected that shall not be used within a hazardous (classified) location. (FPN): Associated apparatus has identified intrinsically safe connections for intrinsically safe apparatus and also may have connections for nonintrinsically safe apparatus. Control Drawing: A drawing or other document provided by the manufacturer of the intrinsically safe or associated apparatus that details the allowed interconnections between the intrinsically safe and associated apparatus. Different Intrinsically Safe Circuits: Different intrinsically safe circuits are intrinsically safe circuits in which the possible interconnections have not been evaluated and approved as intriniscally safe. Intrinsically Safe Apparatus: Apparatus in which all the circuits are intrinsically safe. Intrinsically Safe Circuit: A circuit in which any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under prescribed test conditions. 70-500 NATIONAL ELECTRICAL CODE (FPN): Test conditions are described in Standard for Safety, Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1, Hazardous (Classified) Locations, ANSI/UL 913-1988. Intrinsically Safe System: An assembly of interconnected intrinsically safe apparatus, associated apparatus, and interconnecting cables in that those parts of the system that may be used in hazardous (classified) locations are intrinsically safe circuits. (FPN): An intrinsically safe system may include more than one intrinsically safe circuit. 504-3. Application of Other Articles. Except as modified by this article, all applicable articles of this Code shall apply. 504-4. Equipment Approval. All intrinsically safe apparatus and associated apparatus shall be approved. 504-10. Equipment Installation. (a) Control Drawing. Intrinsically safe apparatus, associated apparatus, and other equipment shall be installed in accordance with the control drawing(s). (FPN): The control drawing identification is marked on the apparatus. (b) Location. Intrinsically safe and associated apparatus shall be permitted to be installed in any hazardous (classified) location for which it has been approved. (FPN): Associated apparatus may be installed in hazardous (classified) locations if protected by other means permitted by Articles 501 through 503. General-purpose enclosures shall be permitted for intrinsically safe apparatus. 504-20. Wiring Methods. Intrinsically safe apparatus and wiring shall be permitted to be installed using any of the wiring methods suitable for unclassified locations. Sealing shall be as provided in Section 504-70, and separation shall be as provided in Section 504-30. 504-30. Separation of Intrinsically Safe Conductors. (a) From Nonintrinsically Safe Circuit Conductors. (1) Open Wiring. Conductors and cables of intrinsically safe circuits not in raceways or cable trays shall be separated at least 2 inches (50.8 mm) and secured from conductors and cables of any nonintrinsically safe circuits. Exception: Where either (1) all of the intrinsically safe circuit conductors are in Type MI, MC, or SNM cables or (2) all of the nonintrinsically safe circuit conductors are in raceways or Type MI, MC, or SNM cables where the sheathing or cladding is capable of carrying fault current to ground. (2) In Raceways, Cable Trays, and Cables. Conductors of intrinsically safe circuits shall not be placed in any raceway, cable tray, or cable with conductors of any nonintrinsically safe circuit. ARTICLE 504 - INTRINSICALLY SAFE SYSTEMS 70-501 Exception No. 1: Where conductors of intrinsically safe circuits are separated from conductors of nonintrinsically safe circuits by a distance of at least 2 inches (50.8 mm) and secured, or by a grounded metal partition or an approved insulating partition. (FPN): No. 20 gauge sheet metal partitions 0.0359 inch (912 micrometers) or thicker are generally considered acceptable. Exception No. 2: Where either (1) all of the intrinsically safe circuit conductors or (2) all of the nonintrinsically safe circuit conductors are in grounded metal-sheathed or metal-clad cables where the sheathing or cladding is capable of carrying fault current to ground. (FPN): Cables meeting the requirements of Articles 330, 334, and 337 are typical of those considered acceptable. (3) Within Enclosures. a. Conductors of intrinsically safe circuits shall be separated at least 2 inches (50.8 mm) from conductors of any nonintrinsically safe circuits, or as specified in Section 504-30(a)(2). b. All conductors shall be secured so that any conductor that might come loose from a terminal cannot come in contact with another terminal. (FPN No. 1): The use of separate wiring compartments for the intrinsically safe and nonintrinsically safe terminals is the preferred method of complying with this requirement. (FPN No. 2): Physical barriers such as grounded metal partitions or approved insulating partitions or approved restricted access wiring ducts separated from other such ducts by at least 3/₄ in. (19 mm) can be used to help assure the required separation of the wiring. (b) From Different Intrinsically Safe Circuit Conductors. Different intrinsically safe circuits shall be in separate cables or shall be separated from each other by one of the following means: (1) The conductors of each circuit are within a grounded metal shield; (2) The conductors of each circuit have insulation with a minimum thickness of 0.01 inches (254 micrometers). Exception: Unless otherwise approved. 504-50. Grounding. (a) Intrinsically Safe Apparatus, Associated Apparatus, and Raceways. Intrinsically safe apparatus, associated apparatus, cable shields, enclosures, and raceways, if of metal, shall be grounded. (FPN): Supplementary bonding to the grounding electrode may be needed for some associated apparatus, e.g., zener diode barriers, if specified in the control drawing. See Installation of Intrinsically Safe Instrument Systems in Class I Hazardous Locations, ANSI/ISA RP 12.6-1987. (b) Connection to Grounding Electrodes. Where connection to a grounding electrode is required, the grounding electrode shall be as specified in Sections 250-81(a), (b), (c), (d) and shall comply with Section 250-26(c). Section 250-83 shall not be used if electrodes specified in Section 250-81 are available. 70-502 NATIONAL ELECTRICAL CODE (c) Shields. Where shielded conductors or cables are used, shields shall be grounded. Exception: Where a shield is part of an intrinsically safe circuit. 504-60. Bonding. (a) Hazardous Locations. In hazardous (classified) locations, intrinsically safe apparatus shall be bonded in the hazardous (classified) location in accordance with Section 250-78. (b) Nonhazardous Locations. In nonhazardous locations, where metal raceways are used for intrinsically safe system wiring in hazardous locations, associated apparatus shall be bonded in accordance with Sections 501-16(a), 502-16(a), or 503-16(a), as applicable. 504-70. Sealing. Conduits and cables that are required to be sealed by Sections 501-5 and 502-5 shall be sealed to minimize the passage of gases, vapors, or dust. Exception: Seals are not required for enclosures that contain only intrinsically safe apparatus except as required by Section 501-5(f)(3). (FPN): It is not the intent of this section to require an explosionproof seal. 504-80. Identification. Labels required by this section shall be suitable for the environment where they are installed with consideration given to exposure to chemicals and sunlight. (a) Terminals. Intrinsically safe circuits shall be identified at terminal and junction locations in a manner that will prevent unintentional interference with the circuits during testing and servicing. (b) Wiring. Raceways, cable trays, and open wiring for intrinsically safe system wiring shall be identified with permanently affixed labels with the wording "Intrinsic Safety Wiring" or equivalent. The labels shall be so located as to be visible after installation and placed so that they may be readily traced through the entire length of the installation. Spacing between labels shall not be more than 25 feet (7.62 m). Exception: Circuits run underground shall be permitted to be identified where they become accessible after emergence from the ground. (FPN No. 1): Wiring methods permitted in nonhazardous locations may be used for intrinsically safe systems in hazardous (classified) locations. Without lables to identify the application of the wiring, enforcement authorities cannot determine that an installation is in compliance with the Code. (FPN No. 2): In nonhazardous locations, the identification is necessary to assure that nonintrinsically safe wire will not be inadvertently added to existing raceways at a later date. (c) Color Coding. Color coding shall be permitted to identify intrinsically safe conductors where they are colored light blue and where no other conductors colored light blue are used.