Glossary

Abrasion Resistance: The ability of a material to tolerate mechanically induced surface wear.

Admittance: The ratio of current to voltage, the reciprocal of impedance. The unit of admittance is the Siemens (S). Admittance is typically abbreviated as "y" or "Y".

Ambient Temperature: The temperature of the medium surrounding an object. The term is often used to denote prevailing room temperature.

American Wire Gage: (AWG) System of numerical designations for wire size, based on specified ranges of circular mil area. American Wire Gauge starts with 4/0 (0000) at the largest size, going to 3/0 (000), 2/0 (00), 1/0 (0), 1, 2, and up to 40 and beyond for the smallest sizes.

Ampere: Abbreviated A or amp. Practical unit of electrical current; the current flow rate (i.e., quantity of electrons passing a point in 1 second). Voltage of 1 volt will send a current of 1 ampere through a resistance of 1 ohm.

Bus Bar: Power distribution device consisting of single or multiple layers of rectangular conductors separated by insulation material and which may be laminated to form a single unit. Outer insulation may be used to isolate the bus bar from other components or to provide safety to end-users.

Capacitance: The property of an electrical nonconductor (dielectric in a capacitor) that permits the storage of energy as a result of electric displacement. The basic unit of capacitance is the Farad, however measurement is more commonly in microfarads or picofarads.

Capacitance Reactance: The opposition to alternating current flow presented by a capacitance. The symbol for capacitive reactance is XC. The unit is the ohm. The formula for capacitive reactance is XC = 1/(2nFC), where F is the frequency of the alternating current signal, and C is the capacitance.

Capacitive Coupling: Desired or undesired interaction between two circuits or conductors caused by the capacitance between them.

Capacitor: A device to store electricity and release it when needed - consisting of conducting plates or foils separated by thin layers of dielectric, the plates on opposite sides of the dielectric layers being oppositely charged by a source of voltage, and the electrical energy of the charged system being stored in the polarized dielectric. (See also capacitance).

Circular Mil: CMA - a unit of area equal to the area of a circle whose diameter is 1 mil (0.001 inch). Used chiefly in specifying cross-sectional areas of conductors. To obtain the number of circular mils in a round solid wire of a given diameter, express the diameter in mils then square it. The CMA formula for stranded conductor is to square the mil diameter of one strand then multiply by the number of strands. (One circular mil is equal to 1/0.7854 sq mils or 1.2732 sq mils)

Clearance: The shortest distance through the air between two conductive elements.

Conductivity: The capability of a material to carry electrical current, usually expressed as a percentage of copper conductivity (copper being 100%). Specifically, the ratio of the current flow to the potential difference causing the flow. The reciprocal of resistance.

Contact Resistance: The DC resistance of a pair of mated contacts.

Creepage: The conduction of electricity across the surface of a dielectric.

Creepage Distance: The shortest distance along the surface of the insulation material between two conductive parts.

Cross-Sectional Area: For planar bus bars, the cross-sectional area of a conductor is the product of the thickness times the width of the conductor. For wires the cross-sectional area is the sum of the cross-section areas (90° cut) of the individual strands in a conductor.

Cross Talk: A magnetic or electrostatic coupling that causes the unwanted transfer of energy from one circuit (disturbing circuit) to another circuit (disturbed circuit).

Current Carrying Capacity: The current a conductor can carry safely without exceeding temperature rise limits.

Derating: The reduction in a rating of a component or device to provide safety margins or to insure satisfactory performance when the parts are subjected to severe operating conditions for which normal ratings do not apply.

Dielectric: The insulating (non-conducting) material between two conductors.

Dielectric Constant: The property of an insulating material, which is the ratio of the capacitance of a capacitor with the given dielectric to the capacitance of a capacitor with an air dielectric (but otherwise identical).

Dielectric Strength: The voltage that an insulating material can withstand without failure. (Normally indicated in volts per mil).

Dissipation Factor: The ratio of the conductance of a capacitor to its susceptance. Also, the ratio of the parallel reactance of a capacitor to its parallel resistance.

EMI (Electromagnetic Interference): Electro-Magnetic Interference - An unwanted electrical energy in any form. EMI is often used interchangeably with 'noise' and 'interference'.

Emissivity: The ratio of the radiant energy emitted by a radiation source to the radiant energy of a perfect radiator with identical dimensions under identical conditions.

Floating Ground: Any ground, or common current path, which is electrically isolated from earth ground or chassis ground.

Harness: A wire assembly involving two or more wires that are prepared and ready for installation into a unit or system.

Hermetic Seal: A gas-tight seal, which permits maximum gas leakage of 1.0-micron ft/hr at one atmosphere pressure.

Hertz: Term for cycles per second by international standard, adopted and now common in the U.S. From the German physicist's name, Heinrich R. Hertz. In use we find that 60 cycles/second (or 60 cps) becomes 60 hertz (or 60 Hz).

Impedance: The total opposition offered by a component or circuit to the flow of alternating or varying current at a particular frequency, including both the AC and DC component. Inpedance is expressed in ohms and is similar to the actual resistance in a direct current circuit. In computations, impedance is handled as a complex ratio of voltage to current. The ohm is the unit of impedance. Impedance is typically abbreviated as "z or "Z". The frequency-invariant, real component of impedance is resistance. The frequency-variant, imaginary component of impedance is reactance. The reciprocal of impedance is admittance.

Inductance: An electromagnetic phenomenon in which the expanding and collapsing of a magnetic field surrounding a conductor or device tends to impede changes in current. The effects of inductance become greater as frequencies increase. Inductance is measured in Henrys, and it is expressed by the equation: L = E / (di/dt).

Inductive Reactance: The opposition to alternating current flow presented by an inductor. The symbol for capacitive reactance is XL = 2nFL, where F is the frequency of the alternating current signal, and L is the inductance.

Inductor: A circuit component designed so that inductance is its most important property. Also called a coil.

Insulation Resistance: The property of a material that resists current flow through the material when a potential difference exists across the material.

IR Drop: The voltage measured across a circuit resistance R, when a current, I flows through that resistance.

Leakage Current: The undesirable current that flows through, or across the surface of an insulating material.

Loss Factor: The product of the dissipation and dielectric constant of an insulating material.

Mil: A unit equal to one one-thousandth of an inch (.001"), equivalent to 0.0254 millimeters or 25.4 micrometers; used in measuring the diameter of a conductor or thickness of insulation over a conductor.

Mho: Unit of conductance. Reciprocal of an ohm. One ampere of current passing through a material under a potential difference of one volt provides one mho of conductance. Also called siemens.

Noise: Random electrical signals, generated by circuit components or by natural disturbances.

RFI: (Radio Frequency Interference): Electromagnetic Interference (EFI) which exists in the frequency spectrum.

Reactance: The Imaginary part of the electrical impedance; a measure of opposition to a sinusoidal alternating current. See Inductive Reactance and Capacitive Reactance.

Resistivity: A physical property of a material to resist or oppose the movement of charge through the material. It is equal to the resistance of the material (in ohms) x (area of sample / length of sample). Typically expressed in ohm-cm, or ohm x Sq mm/m, or ohm x Sq mil/ft.

Shield: The metallic layer applied over or between dielectrics to prevent electrostatic or electromagnetic interference between the enclosed conductors and external fields.

Skin Effect: The tendency for alternating current to flow mostly near the outer surface of a solid electrical conductor, such as metal wire or rectangular bus, at frequencies above the audio range. The effect becomes more and more apparent as the frequency increases. At medium to high frequencies the skin effect essentially reduces the effective cross sectional area of the conductor and increases the resistance.

Square Mil: The area of a square, which mesaures on mil (0.001") by one mil (0.001"). Thus one square mil is equal to 0.000001 in2, or 1x10-6in (one square mil is equal to 0.7854 circular mils).

Susceptance: the imaginary part of admittance.

Temperature Coefficient of Resistivity: The ratio of the change in resistivity to the original resistivity value, for a unit change in temperature.

Voltage Drop: The voltage developed across a component or conductor by the flow of current through the resistance or impedance of that component or conductor. Often simply called voltage. Also called "drop". The voltage across a resistor is usually called IR drop, while that in a conductor is usually called resistance drop.

Watt: The unit for power, abbreviated as "W", equal to 1 joule per second. The practical unit of electric power. In a dc circuit, the power in watts is equal to voltage multiplied by current. In an ac curcuit, the true power in watts is effective voltage multiplied by effective current, then multiplied by the circuit power factor. Ther are 746 watts in 1 horsepower.

Wire Wrap: A method of connecting a wire by wrapping it tightly around a square, rectangular or V-shaped terminal.