UL 988-2020 pdf download – Humidifiers.
5 Enclosures 5.1 General 5.1.1 Products shall be constructed so that they have the strength and rigidity necessary to resist the abuse to which they might be subjected, without increasing the risk of fire, electric shock, or injury to persons, due to partial collapse with resultant reduction of spacings, loosening or displacement of parts, or other defects. 5.1.2 In determining compliance with Clause 5.1.1, all elements that contribute to the enclosing function, including enclosures of individual components and the exterior (decorative) cabinet, shall be considered. 5.1.3 Enclosures made in the form of grilles, etc., of wire or sheet metal, and intended to accommodate air flow required for the operation of the equipment, shall be considered to comply with Clause 5.1.1 if they provide resistance to deflection or impact that would be acceptable to the requirements specifed in Clause 5.1.4 for enclosures of sheet metal. 5.1.4 Unless the surface under consideration is curved, ribbed, or otherwise reinforced, cast and sheet- metal sections of an enclosure shall not be thinner than as specified in Table 1. 5.1.5 A metal plate or metal plug used to cover an unused conduit opening or other hole that is required to be covered in the enclosure shall have a thickness not less than: a) 0.35 mm (0.014 in) if steel, or 0.48 mm (0.019 in) if nonferrous metal, for a hole having a 6.4 mm (1/4 in) maximum dimension; and b) 0.68 mm (0.027 in) if steel, or 0.81 mm (0.032 in) if nonferrous metal, for a hole having a 34.9 mm (1-3/8 in) maximum dimension. A closure for a larger hole shall have a thickness no less than that required for the enclosure of the product. Such plates or plugs shall be securely mounted.
17 Protection Against Corrosion 17.1 If corrosion of a part could result in a risk of fire, electric shock, or injury to persons, such a part shall be plated, painted, or the equivalent. Phosphate treatment with an oil or wax coating may be used for protecting magnets and armatures. Oil treatment may be used for steel springs. Stainless steel shall be acceptable without additional protection if it is polished or treated when necessary. 17.2 Metals shall be used in combinations that are galvanically compatible if galvanic action could adversely affect any cabinet, enclosure, or other parts. 17.3 Each hinge and other attachment shall be resistant to corrosion. 18 Cord-Connected Products 18.1 Equipment other than plenum- or duct-mounted humidifiers may be cord connected if: a) The voltage rating does not exceed 250 V; b) It will start and operate as intended from a circuit with a 30 A overcurrent protection (see Starting Test, Clause 55); or c) The marked rating does not exceed 24 A. 18.2 Plenum- or duct-mounted humidifiers may be cord connected if: a) The voltage rating does not exceed 150V; b) The current rating does not exceed 12 A; c) A branch circuit overcurrent protection of not more than 15 A is required for satisfactory starting and operating; and d) The design does not require that field-wiring connections operating at above 30 V shall be made at the time of installation to a furnace control or to a control for the humidifier.