UL 1581 is a standard for testing electrical wires, cables, and flexible cords. The vertical flame test is one of the tests specified in this standard, which determines the flammability of the insulation or jacket material used in these products.
During the vertical flame test, a wire or cable sample is exposed to a small flame for a specified period of time, and various parameters such as flame spread distance, drip flaming, and sustained combustion are observed and measured. The test is intended to evaluate the ability of the insulation or jacket material to resist ignition and prevent the spread of flames.
The UL 1581 standard specifies the testing procedures and criteria for pass/fail determination for the vertical flame test, and compliance with this standard is often required by regulatory bodies and industry organizations to ensure product safety and performance.