Formerly designated as "FR-1," it is a rating established by UL for wire and cables that pass a specifically designed vertical flame test for flammability. – Any cord that is designated by Underwriters Laboratories, Inc. (UL) for outdoor use.
Basic flammability test for single conductors; employs a tirrill burner applied intermittently to a Vertical Wire.
A flammability rating established by Underwriters Laboratories for wires and cables that pass a specially designed vertical flame test, formerly designated FR-1.