UL 506-2009 pdf download – Specialty Transformers.
3 Glossary 3.1 For the purpose of this standard, the following definitions apply. 3.2 COMPOUND-FILLED TRANSFORMER – A transformer in which the windings are enclosed with an insulating fluid that becomes solid, or remains plastic, at intended operating temperatures. 3.3 ENCAPSULATED COIL – A coil that is enclosed with an insulating fluid that becomes solid. 3.4 EXPOSED CORE TRANSFORMER – A transformer with exposed core lamination. 3.5 NONVENTILATED DRY-TYPE TRANSFORMER – A dry-type transformer other than of the compound-filled or exposed core-type that is constructed so as to provide no intentional circulation of ambient air through the transformer and is intended to operate at normal ambient room air pressure. 3.6 VENTILATED DRY-TYPE TRANSFORMER – A dry-type transformer that is constructed so that ambient air may circulate through the enclosure to cool the transformer core and windings. 3.7 WINDING – A continuous conductor made up of a number of turns magnetically coupled to a magnetic core, to which a voltage is either applied or induced. Two or more such conductors that are permanently factory connected together to form intermediate voltage taps, current taps, or the like are considered to be a single winding. The winding can consist of single or parallel-wound conductors.
4 Mechanical Assembly 4.1 A transformer shall be formed and assembled so that it will have the strength and rigidity necessary to resist the abuses to which it is likely to be subjected. A risk of fire, electric shock, or injury to persons shall not result from a reduction of spacings, loosening or displacement of parts, or other serious defect due to total or partial collapse of the transformer. 5 Enclosure 5.1 In addition to the overall enclosure, the requirements in 5.2 – 5.1 5 apply to those portions of an enclosure surrounding a terminal or wiring compartment. 5.2 A sheet steel enclosure shall be formed from stock having a thickness of not less than 0.026 inch (0.66 mm) if uncoated or not less than 0.029 inch (0.74 mm) if zinc coated. Exception: Sheet steel having a thickness of not less than 0.020 inch (0.51 mm) if uncoated or not less than 0.023 inch (0.58 mm) if zinc coated may be used for drawn end bells having a maximum width or length of 2-1 /4 inches (57.2 mm) on the flat portion and 1 -1 /2 inches (38.1 mm) at the base of the drawn portion. Figure 5.1 illustrates these portions of an end bell.