UL Approved -- Designating a product or device which has been inspected, tested and approved by the Underwriters' Laboratories, Inc. See Underwriters' Laboratories, Inc. Cable will have the UL trademark or the "E" listing number printed on the jacket when approved.

Ultimate Strength -- Term used to describe the maximum unit stress a material will withstand when subjected to an applied load in a compression, tension or shear test.

Ultraviolet Degradation -- The degradation caused by long time exposure of a material to sunlight or other ultraviolet rays containing radiation.

Unbalanced Line -- A transmission line in which voltages on the two conductors are unequal with respect to ground or another pair of conductors.

Underground Cable -- Cable installed in below ground conduits or ducts. Usually terminates at certain intervals in manholes, allowing for the easy placing, replacing or removal of the cables.

Underwriter's Laboratories, Inc. -- A non-profit laboratory sponsored by the National Board of Fire Underwriters which examines and tests devices, materials and systems whose action may affect casualty, fire and life hazards. See CM, CMP, CMR, CMX and UL definitions.

Unidirectional Concentric Stranding -- A unidirectional stranding is where each successive layer has a different lay length, thereby, retaining a circular form without migration of strands form one layer to another.

Unidirectional Stranding -- A term denoting that in a stranded conductor all layers have the same direction lay.

Unilay -- A conductor with more than one layer of helically laid wires with the direction of lay and length of lay the same for all layers.

Unilay Stranding -- A bunched construction having 19, 27, 37 or any number of stands which might be found in a concentric stranding.

Units -- The grouping of twinned conductors used in forming a cable. Usually 25 pairs. The units may be divided into such units of 12 and 13 pairs or 8 and 9 pairs.