Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

chain reaction
a process in which high-energy neutrons emitted from fissile radioactive material are directed into more fissile material such that more neutrons are emitted. The process creates heat which is used to power thermal power plants.
charge conservation
physical law (derived from Maxwell's equations) indicating that no change in the total charge within a
certain volume can exist without the proper flow of charge (current) through that volume.
charging current
that portion of an electric power line's current which goes to charge the capacitance of the line. The charging current is not available for power transmission.
chemical laser
a laser in which the amplification results from one or more chemical reactions; potentially very powerful with principal output lines in the mid-infrared.
circle diagram
(1) graphical representation of the operation of an induction machine. It is based on the approximate equivalent circuit and expresses stator and rotor current relations for all operating modes (motor, braking, generator) and all values of slip. Several variations of the diagram exist.
(2) graphical representation of the power flow through a transmission line. The maximum power flow through the line can be determined by the impedance of the line.
a physical device consisting of an interconnection of elements, or a topological model of such a device. For example, an electric circuit may be constructed by interconnecting a resistor and a capacitor to a voltage source.
circuit breaker
a circuit breaker is a device that makes and breaks the electrical contact between its input and output terminals. The circuit breaker is capable of clearing fault currents (tripping) as well as load currents. The circuit breaker consists of power contacts with arc clearing capability and associated control and auxiliary circuits for closing and tripping the breaker under the required conditions.
circuit protection
devices or control measures used to safeguard electrical circuits from unsafe operating regions, such as over-currents and over-voltages.
circular mil
the area of a circle which measures 0.001 inch in diameter. Used to specify the cross-sectional area of a wire.
circular polarization
a polarization state of a radiated electromagnetic field in which the tip of the electric field vector traces a circle as a function of time for a fixed position. The sense of rotation of the electric field vector is either right-hand or left-hand (clockwise or counter-clockwise).

See coaxial cable
coaxial cable
A transmission line formed by two concentric conductors separated by a dielectric designed to confine the fields and their energy in the medium between said conductors. It is often used in applications where signal interference between the cable and its surrounds must be kept to a minimum.

See coax
code letter

See NEMA code letter
coefficient of thermal expansion (CTE) mismatch
the difference between the coefficients of thermal expansion of two components, i.e., the difference in linear thermal expansion per unit change in temperature. (This term is not to be confused with thermal expansion mismatch).
coefficient of utilization (CU)
the ratio of the lumens reaching the working plane to the total lumens generated by the lamp. This factor takes into account the efficiency and distribution of the luminaire, its mounting height, the room proportions, and the reflectances of the walls, ceiling, and floor.

See cogeneration
(1) any of a number of energy generation systems in which two (or more) forms of energy are produced in forms practical for use or purchase by an end user. Typical systems produce electrical energy for sale to a utility and process steam for local space heating or other process uses. Cogeneration designs are generally adopted to increase the overall efficiency of a power generation process.
(2) typically, the production of heat energy, e.g. to heat buildings, as an adjunct to the production of electric power.
coherent illumination
a type of illumination resulting from a point source of light that illuminates the mask with light from only one direction. This is more correctly called "spatially coherent illumination."
coherent light
light having a relatively long coherence length; laser light.
a conductor shaped to form a closed geometric path. Note that the coil will not be a closed conducting path unless the two ends of the coil are shorted together. Coils may have multiple turns, and may have various constructions including spool, preformed, and mush-wound. The coil may be wrapped around an iron core or an insulating form, or it may be self-supporting. A coil offers considerable opposition to AC current but very little to DC current.