UL 224:2021 PDF Download

UL 224:2021 is a standard that specifies the requirements for extruded insulating tubing. The tubing is typically round in cross-section and is made of thermosetting, elastomeric, or thermoplastic polymers. The standard also covers heat-shrinkable and crosslinked tubing.

The intended use of the tubing is for internal wiring of electrical devices and appliances in dry and damp locations. It is designed to insulate inadequately insulated conductors, bus bars, motor leads, transformer leads, terminal lugs, or small assemblies of electronic components. However, it is not intended for use in areas where it may come into contact with sharp edges, corners, projections, tension, compression, or repeated flexing. It is also not suitable for situations where standard insulated conductors specifically designed for the purpose are available.

The standard does not apply to fabric tubing, chemically dilated tubing, polymeric tubing extruded with reinforcement, or tubing intended solely for mechanical protection. The acceptability of the tubing for a specific device or appliance depends on its ability to continue functioning under the conditions present in actual service. In some cases, additional features may be required beyond those specified in the standard, such as a heavier wall thickness or a non-round cross-section. The tubing may also need to have resistance to immersion in water, oil, solvents, or other liquids, or be suitable for use in environments conducive to fungal growth.