UL 551:2018 pdf download.Transformer-Type Arc-Welding Machines.
10.3.4 Means shall be provided so that the flexible cord cannot be pushed into the enclosure through thecord-entry hole if such displacement is likely to:
a) Subject the cord to mechanical damage,
b) Expose the cord to a temperature higher than that for which it is rated, or
c) Reduce spacings, such as to a metal strain relief clamp, below the minimum acceptablevalues.
10.3.5 lf a knot in a flexible cord serves as a strain relief, the surface against which the knot may bear orwhich it may contact shall be free from projections,sharp edges, burrs,fins, or the like that may causeabrasion of the cord insulation.
10.3.6 At a point where a flexible cord passes or is intended to pass through an opening in a wall, barrier,or enclosing case, there shall be a bushing or the equivalent that is substantial, secured in place,andsmoothly rounded on the surface against which the cord may bear.
10.3.7 Ceramic materials, some molded compositions, smooth metal grommets,or the equivalent areacceptable for bushings,but a separate bushing of wood，rubber，or hot-molded shellac-and-tarcomposition is not acceptable.
10.4 Wiring terminals and leads
10.4.1 Other than as noted in 10.4.10, a product that is not provided with an attached flexible cord shallhave wiring terminals or supply leads for the connection of supply conductors sized in accordance withTable 10.3 with the ampacity based on the value determined from the formula in 10.2.4.
