the insulation system.
450.12 Terminal Wiring Space. The minimum wire- bending space at fixed, 600-volt and below terminals of transformer line and load connections shall be as required in 312.6. Wiring space for pigtail connections shall conform to Table 314.16(B).
450.13 Accessibility. All transformers and transformer vaults shall be readily accessible to qualified personnel for inspection and maintenance or shall meet the requirements of 450.13(A) or 450.13(B).
(A) Open Installations. 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.
(B) Hollow Space Installations. Dry-type transformers
600 volts, nominal, or less and not exceeding 50 kVA
shall be permitted in hollow spaces of buildings not
permanently closed in by structure, provided they meet
the ventilation requirements of 450.9 and separation
from combustible materials requirements of 450.21(A).
Transformers so installed shall not be required to be
readily accessible.
II. Specific Provisions Applicable to Different Types of
Transformers
450.21 Dry-Type Transformers Installed Indoors. (A) Not over 112Vi kVA. Dry-type transformers
installed indoors and rated 112'/2 kVA or less shall have
a separation of at least 300 mm (12 in.) from
combustible material unless separated from the
combustible material by a fire-resistant, heat-insulated
barrier.
Exception: This rule shall not apply to transformers rated for 600 volts, nominal, or less that are completely enclosed, with or without ventilating openings.
(B) Over 112 1/2 kVA. Individual dry-type transformers of more than 112'/2 kVA rating shall be installed in a trans former room of fire-resistant construction. Unless specified otherwise in this article, the term fire resistant means a construction having a minimum fire rating of 1 hour.
Exception No. 1: Transformers with Class 155 or higher insulation systems and separated from combustible material by afire-resistant, heat-insulating barrier or by not less than 1.83 m (6 ft) horizontally and 3.7 m (12 ft) vertically.
Exception No. 2: Transformers with Class 155 or higher insulation systems and completely enclosed except for ventilating openings.
FPN: See ANSI/ASTM El 19-1995, Method for Fire Tests of Building Construction and Materials, and NFPA 251-
2006, Standard Methods of Tests of Fire Resistance of
Building Construction and Materials.
(C) Over 35,000 Volts. Dry-type transformers rated over
35,000 volts shall be installed in a vault complying with
Part III of this article.
450.22 Dry-Type Transformers Installed Outdoors.
Dry-type transformers installed outdoors shall have a weatherproof enclosure.
Transformers exceeding 112'/2 kVA shall not be located within 300 mm (12 in.) of combustible materials of buildings unless the transformer has Class 155 insulation systems or higher and is completely enclosed except for ventilating openings.
450.23 Less-Flammable Liquid-Insulated Transformers.
Transformers insulated with listed less-flammable liquids that have a fire point of not less than 300°C shall be permitted to be installed in accordance with
450.23(A) or 450.23(B).
(A) Indoor Installations. Indoor installations shall be per mitted in accordance with one of the following:
(1) In Type I or Type II buildings, in areas where all of the following requirements are met:
a. The transformer is rated 35,000 volts or less. b. No combustible materials