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The Book of Terms

The Book of TermsThe WJI Book of Wire & Cable Terms: an interactive experience of learning and sharing
This book, written by industry volunteers and containing more than 5,000 entries, is an asset for newcomers to wire and cable.

At the same time, it also represents an opportunity for industry veterans to give back by either updating or adding to the more than 5,000 entries. This is an honor system process. Entries/updates must be non-commercial, and any deemed not to be so will be removed. Share your expertise as part of this legacy project to help those who will follow. Purchase a printed copy here.


All   0-9   A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

U-Bend Test

See Test, U-Bend.


Designation for underground distribution.


Designation for underground feeder and branch circuit cable, thermoplastic insulated, 60°C (140°F), wet and dry locations, including direct burial.


Designation for Universal Govern­ment. A two-letter designation that precedes the number on connectors for coaxial cable.


Designation for Ultra-High Frequency. A fre­quency in the band between 300 and 3,000 Mhz.


Designation for Underwriters’ Laboratories, a non-profit independent organization, which operates a listing service for electrical and electronic materials and equipment. (Canadian counterpart is CSA).

UL Approved

A product that has been tested and approved to Underwriters Laboratories’ standards.

Ultimate Tensile Strength

See Tensile Strength.

Ultrasonic Cleaning

Cleaning aided by the application of high frequency sound waves in a cleaning solution. The high frequency sound waves are produced by transducers that convert electrical energy to mechanical energy causing microagitation. Microagitation results in localized low and high pressure fronts. At a low pressure front the solution vaporizes (boils) to form tiny bubbles. At a high pressure front these bubbles implode (cavitate) producing intense shock waves. It is the cavitation of a multitude of tiny bubbles to both exposed and hidden crevices that enables ultrasonics to clean the surface of components and precision parts (including the holes of diamond drawing dies) as well as removal of lubricant and loose scale on wire.

Ultrasonic Cutting, Die

Technique of piercing a natural diamond in preparation for the manufacture of a diamond die.

Ultrasonic Detector

A device that detects the ultrasonic noise such as that produced by a corona or leaking gas.

Ultrasonic Gauge

A non-destructible test instrument using the principle of ultrasonic resonance to establish the thickness of metals and plastics. Mechanical vibrations are sent into the material under test, and the resonant frequency returning from the sample appears as two or more vertical traces on a cathode ray tube. It can be used for quality control in the production of such items as lead-sheathed cable.

Ultrasonic Testing

A nondestructive test applied to sound-conductive materials having elastic properties for the purpose of locating inhomogeneties or structural discontinuities within a material by means of an ultrasonic beam.

Ultrasonic Waves

Wave of acoustical radiation higher than about 20 kHz, i.e., higher than the range of audible sound. They include longitudinal, transverse, surface and standing waves.


Radiant energy within the wavelength range 10 to 380 nanometers.

Ultraviolet Degradation

Degradation caused by long-term exposure of a material to sunlight or other ultraviolet rays containing radiation. This can be a concern for the jacketing of cables, which can experience voltage breakdown as the jacketing degrades.

Ultraviolet Inhibitor

Chemicals in a PVC insulation compound that protect the insulation from breaking down when exposed to sunlight.

Unbalanced Circuit or Line

A transmission line in which voltages on the two conductors are unequal with respect to ground, i.e., a coaxial cable.

Uncropped Coils

Coils not sheared to length following hot rolling.


Less than normal operating current.

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