Resolución 2535: adopta el Código Eléctrico Nacional, versión 1993. (Sustituye el Anejo A del Reglamento 4435)

501-6. Switches, Circuit Breakers, Motor Controllers, and Fuses. (a) Class I, Division 1. In Class I, Division 1 locations, switches, circuit breakers, motor controllers, and fuses, including pushbuttons, relays, and similar devices, shall be provided with enclosures, and the enclosure in each case, together with the enclosed apparatus, shall be approved as a complete assembly for use in Class I locations. (b) Class I, Division 2. Switches, circuit breakers, motor controllers, and fuses in Class I, Division 2 locations shall comply with the following: (1) Type Required. Circuit breakers, motor controllers, and switches intended to interrupt current in the normal performance of the function for which they are installed shall be provided with enclosures approved for Class I, Division 1 locations in accordance with Section 501-3(a), unless general-purpose enclosures are provided and (1) the interruption of current occurs within a chamber hermetically sealed against the entrance of gases and vapors, or (2) the current make-and-break contacts are oil-immersed and of the general-purpose type having a 2-inch (50.8-mm) minimum immersion for power contacts and a 1-inch (25.4-mm) minimum immersion for control contacts, or (3) the interruption of current occurs within a factory-sealed explosionproof chamber approved for the location. (2) Isolating Switches. Fused or unfused disconnect and isolating switches for transformers or capacitor banks that are not intended to interrupt current in the normal performance of the function for which they are installed shall be permitted to be installed in general-purpose enclosures. (3) Fuses. For the protection of motors, appliances, and lamps, other than as provided in (b)(4) below, standard plug or cartridge fuses shall be permitted, provided they are placed within enclosures approved for the location; or fuses shall be permitted if they are within general-purpose enclosures, and if they are of a type in which the operating element is immersed in oil or other approved liquid, or the operating element is enclosed within a chamber hermetically sealed against the entrance of gases and vapors. (4) Fuses or Circuit Breakers for Overcurrent Protection. Where not more than ten sets of approved enclosed fuses or not more than ten circuit 70-480 NATIONAL ELECTRICAL CODE breakers that are not intended to be used as switches for the interruption of current are installed for branch-circuit or feeder protection in any one room, area, or section of the Class I, Division 2 location, general-purposetype enclosures for such fuses or circuit breakers shall be permitted if the fuses or circuit breakers are for the protection of circuits or feeders supplying lamps in fixed positions only. (FPN): A set of fuses is all the fuses required to protect all the ungrounded conductors of a circuit. For example, a group of three fuses protecting an ungrounded 3-phase circuit and a single fuse protecting the ungrounded conductor of an identified 2-wire, single-phase circuit is a set of fuses in each instance. Fuses complying with (b)(3) above shall not be required to be included in counting the ten sets of fuses permitted in general-purpose enclosures. (5) Fuses Internal to Lighting Fixtures. Approved cartridge fuses shall be permitted as supplementary protection within lighting fixtures. 501-7. Control Transformers and Resistors. Transformers, impedance coils, and resistors used as, or in conjunction with, control equipment for motors, generators, and appliances shall comply with (a) and (b) below. (a) Class I, Division 1. In Class I, Division 1 locations, transformers, impedance coils, and resistors, together with any switching mechanism associated with them, shall be provided with enclosures approved for Class I, Division 1 locations in accordance with Section 501-3(a). (b) Class I, Division 2. In Class I, Division 2 locations, control transformers and resistors shall comply with the following: (1) Switching Mechanisms. Switching mechanisms used in conjunction with transformers, impedance coils, and resistors shall comply with