TRANSFORMERS AND TRANSFORMER VAULTS 70-451

Transformers with ventilating openings shall be installed so that the ventilating openings are not blocked by walls or other obstructions. The required clearances shall be clearly marked on the transformer. 450-10. Grounding. Exposed noncurrent-carrying metal parts of transformer installations, including fences, guards, etc., shall be grounded where required under the conditions and in the manner specified for electric equipment and other exposed metal parts in Article 250. 450-11. Marking. Each transformer shall be provided with a nameplate giving the name of the manufacturer; rated kilovolt-amperes; frequency; primary and secondary voltage; impedance of transformers 25 kVA and larger; required clearances for transformers with ventilating openings; and the amount and kind of insulating liquid where used. In addition, the nameplate of each dry-type transformer shall include the temperature class for the insulation system. 450-12. Terminal Wiring Space. The minimum wire bending space at fixed, 600 volts and below terminals of transformer line and load connections shall be as required in Section 373-6. Wiring space for pigtail connections shall conform to Table 370-16(b). 450-13. Location. Transformers and transformer vaults shall be readily accessible to qualified personnel for inspection and maintenance. Exception No. 1: Dry-type transformers 600 volts, nominal, or less, located in the open on walls, columns, or structures, shall not be required to be readily accessible. Exception No. 2: Dry-type transformers not exceeding 600 volts, nominal, and 50 kVA shall be permitted in fire-resistant hollow spaces of buildings not permanently closed in by structure and provided they meet the ventilation requirements of Section 450-9. Unless specified otherwise in this article, the term "fire-resistant" means a construction having a minimum fire rating of 1 hour. (FPN No. 1): See Method for Fire Tests of Building Construction and Materials, ANSI/ASTM E119-83, and Methods of Fire Tests of Building Construction and Materials, NFPA 251-1990. (FPN No. 2): The location of different types of transformers is covered in Part B of Article 450. The location of transformer vaults is covered in Section 450-41. B. Specific Provisions Applicable to Different Types of Transformers 450-21. Dry-type Transformers Installed Indoors. (a) Not Over 1121/2 kVA. Dry-type transformers installed indoors and rated 112½ kVA or less shall have a separation of at least 12 inches (305 mm) from combustible material. Exception No. 1: Where separated from the combustible material by a fire-resistant, heat-insulating barrier. Exception No. 2: Transformers 600 volts, nominal, or less completely enclosed, with or without ventilating openings. 70-452 NATIONAL ELECTRICAL CODE (b) Over 1121/2 kVA. Individual dry-type transformers of more than 112½ kVA rating shall be installed in a transformer room of fire-resistant construction. Exception No. 1: Transformers with 80°C rise or higher ratings and separated from combustible material by a fire-resistant, heat-insulating barrier or by not less than 6 feet (1.83 m) horizontally and 12 feet (3.66 m) vertically. Exception No. 2: Transformers with 80°C rise or higher ratings and completely enclosed except for ventilating openings. (c) Over 35,000 Volts. Dry-type transformers rated over 35,000 volts shall be installed in a vault complying with Part C of this article. 450-22. Dry-type Transformers Installed Outdoors. Dry-type transformers installed outdoors shall have a weatherproof enclosure. Transformers exceeding 112½ kVA shall not be located within 12 inches (305 mm) of combustible materials of buildings. Exception: Transformers with 80°C rise or higher ratings and completely enclosed except for ventilating openings. 450-23. Less-Flammable Liquid-Insulated Transformers. Transformers insulated with listed less-flammable liquids shall be permitted to be installed without a vault in Type I and Type II buildings in areas in which no combustible materials are stored, provided there is a liquid confinement area, the liquid has a fire point of not less than 300°C, and the installation complies with all restrictions provided for in the listing of the liquid. Such indoor transformer installations not meeting the restrictions of the liquid listing, or installed in other than Type I or Type II buildings, or in areas where combustible materials are stored, shall (1) be provided with an automatic fire extinguishing system and a liquid confinement area or (2) be installed in a vault complying with Part C of this article. Transformers installed indoors and rated over 35,000 volts shall be installed in a vault. Less-flammable liquid-insulated transformers shall be permitted to be installed outdoors attached to, adjacent to, or on the roof of Type I or Type II buildings. Such installations attached to, adjacent to, or on the roof of other than Type I or Type II buildings, adjacent to combustible material, fire escapes, or door and window openings, shall be provided with one or more safeguards according to the degree of hazard. Fire barriers, space separation, and compliance with all of the requirements provided for in the listing of the liquid are recognized safeguards. (FPN No. 1): As used in this section, "noncombustible" refers to Type I and Type II building construction and noncombustible materials as defined in Types of Building Construction, NFPA 220-1992 (ANSI). (FPN No. 2): See definition of "Listed" in Article 100. 450-24. Nonflammable Fluid-Insulated Transformers. Transformers insulated with a dielectric fluid identified as nonflammable shall be permitted to be installed indoors or outdoors. Such transformers installed indoors