UL-5085-1:2011 pdf free download – Underwriters Laboratories Inc. Standard for Safety LoW Voltage Transformers – Part 1: General Requirements.
6.6 Barriers for openings
6.6.1 A barrier that is not an integral part of the enclosure intended for enclosure openings shall comply with the requirements specified in Clauses 6.6.3 — 6.6.6.
6.6.2 Transformers shall be constructed so that molten or flaming particles cannot fall on the surface on or over which the transformer is mounted.
Note: This requirement does not apply to transformers intended for floor-mounting marked in accordance with Clause
17.2.3.
6.6.3 When a barrier is provided for compliance with Clause 6.6.2, it shall be located and situated as illustrated in Figure 2.
6.6.4 A sheet-metal barrier shall be at least 1.35 mm (0.053 in) thick when uncoated steel, 1.42 mm (0.056 in) thick when zinc-coated, or 1 .91 mm (0.075 in) thick when aluminum.
Note: A metal barrier may be of thinner metal provided its strength and rigidity are not less than that of a flat sheet of steel having the same dimensions as the barrier and of the specified thickness.
6.6.5 For bottom openings, a perforated metal barrier shall be constructed with a metal screen, or the equivalent, having 14 x 14 mesh and wire with a minimum diameter of 0.46 mm (0.018 in) or the perforated metal panel shall comply with the Hot, Flaming Oil Test in Clause 23 and Figure 2. A ventilated bottom panel not meeting these construction requirements shall also be subjected to this test.
6.6.6 A polymeric barrier shall comply with the applicable requirements of Nonmetallic enclosures in Clause 6.2. A polymeric barrier that is not an integral part of the enclosure shall be rated minimum V-2.
6.7 Covers
6.7.1 When doors and covers are provided for enclosures, they shall be hinged:
a) When they provide access to normal operating renewable fuses, thermal cutoffs, or other protective devices or
b) When opening covers for normal operation of the transformer are necessary.
6.7.2 When doors or covers provide access to protective devices, they shall shut closely against a minimum 6.3 mm (0.25 in) rabbet or shall have close-fitting flanges that overlap at least 12.7 mm (0.5 in). Any other construction affording equivalent protection shall be subject to investigation.
6.7.3 When they are provided to comply with Clause 6.7.1, hinged doors or covers shall not depend solely on screws or other similar means requiring the use of a tool to hold them closed. They shall be provided with a spring latch or catch unless the screws are captive. For doors or covers other than those required by Clause 6.7.1 a hasp, sliding latch, or other means may be used to hold them closed.
6.7.4 The cover of an enclosure shall be provided with means (such as screws) for firmly securing it in place. Friction alone shall not be used.
6.7.5 A cover that must be removed for the connection of circuit conductors shall not be provided with means for the connection of conduit or armored cable.
6.7.6 A transformer mounted on an outlet box cover and provided with secondary leads emanating from a flexible conduit connector may be used when the volt-ampere and secondary voltage ratings are not more than 100 VA and 30 V, respectively.
7 Corrosion Resistance
7.1 The internal and external surfaces of an enclosure of iron or steel (other than stainless steel) shall be corrosion resistant. Examples of corrosion resistance that comply with these requirements are galvanizing, plating, and enameling.
Note: An interior surface covered by a compound is not required to be additionally resistant to corrosion.
7.2 A Type 3R enclosure made of sheet steel (other than stainless steel) having a thickness of 3.05 mm (0.120 in) or more shall be made corrosion resistant by one of the following coatings.