# Glossary

a resistor so constructed that its resistance can be readily changed.*

Alternating Current:

Ambient Temperature:

the temperature of the surrounding coiling medium, such as gas or liquid, which comes into contact with heated parts of the apparatus.*

Ampere:

the unit of constant current which, maintained in two parallel rectilinear conductors of infinite length separated by a distance of one meter, produces between these conductors a force equal to 2x10-7 mks (meter-kilogramsecond) units of force per meter of length.

Armature Resistor:

a resistor connected in series with the armature of a motor either to limit the inrush current on starting, the gradual short circuiting of which brings the motor to normal speed, or to regulate the speed by armature-voltage control.

Axiohm†:

Bracket Terminal Resistor:

Capacitance:

Capacitor:

Clearance:

the shortest distance through space between two live parts, between live parts and supports or other objects, or between any live part and grounded part.

Conduction:

the transmission of heat or electricity through, or by means of, a conductor.

Conductor:

a body so constructed from conducting material that it may be used as a carrier of electric current.*

Continuous Duty:

Continuous Rating:

continuous rating is the rating that defines the load which can be carried for an indefinitely long time.*

Continuous-Duty Resistor:

a resistor that is capable of carrying continuously the current for which it is designed without exceeding the specified temperature rise.

Convection:

convection is the motion resulting in a fluid owing to differences of density and the action of gravity.

Corrib®†:

Creepage Distance:

Current-limiting Resistor:

a resistor inserted into an electric circuit to limit the flow of current to some predetermined value. note: a currentlimiting resistor, usually in series with a fuse or circuit breaker, may be employed to limit the flow of circuit or system energy at the time of a fault or short-circuit.*

Current-limiting Resistor:

Dielectric Strength:

Dielectric Test:

a test which consists of the application of a voltage higher than the rated voltage for a specified time for the purpose of determining the adequacy against breakdown of insulating materials and spacings under normal conditions.*

Direct Current:

a unidirectional current in which the changes in value are either zero or so small that they may be neglected. a given current would be considered a direct current in some applications, but would not necessarily be so considered in other applications.*

Dividohm®†:

a resistor with a bare side and clamp for adjustment.

EIA:

Edgeohm†:

a high-current resistor made of an alloy resistance ribbon wound on edge forming an oval-shaped coil supported by grooved insulators which space adjacent turns and insulate them from the support bars. support bars are secured to steel end pieces forming a sturdy resistor suitable for continuous-andintermittent-duty applications.

Electromotive Force:

the electromotive force is the agency causing the flow of current in a circuit. it is the electrical pressure (or drop) measured in volts.

the unit of capacitance of an electric condenser in which a charge of one coulomb produces a difference of potential of one volt between the poles of the capacitor.

Ferrule Resistor:

Field Discharge Switch:

a switch usually of the knife blade type having auxiliary contacts for connecting the field of a generator or motor across a resistor (field discharge) at the instant preceding the opening of the switch.

Fixed Resistor:

Henry:

the unit of inductance of a closed circuit in which an electromotive force of one volt is produced when the electric current traversing the circuit varies uniformly at the rate of one ampere per second.

Hot Spot:

the point or location of maximum temperature on the external surface of a resistor.

Impedance:

Inductance:

the (scalar) property of an electric circuit or of two neighboring circuits which determines the electromotive force induced in one of the circuits by a change of current in either of them.*

Intermittent Duty:

Intermittent-Duty Resistor:

a resistor capable of carrying for a short period of time the high overload current for which it is designed without exceeding the specified temperature rise.

MIL Resistor:

a resistor built in accordance with joint army-navy specifications.

Machine-Duty Resistor:

a resistor for use in the armature or rotor circuit of a motor in which the armature current is almost constant.

Mega Ohm:

a unit of resistance equal to one million ohms.

Multi-Section Resistor:

a resistor having two or more electrically independent sections.

NEC:

the national electrical code is the standard of the national board of fire underwriters for electric wiring and apparatus as recommended by the national fire protection association and approved by the american standards association.

NEDA:

national electronic distributors association.

NEMA:

Nominal Diameter:

as applied to tubular resistors, this is the diameter of the ceramic tube expressed in inches and/or fractions thereof.

Nominal Length:

Non-Inductive Resistor:

Ohm:

Ohmmeter:

an instrument for measuring electric resistance that is provided with a scale graduated in ohms.

Periodic Duty:

Periodic Rating:

the rating which defines the load which can be carried for the alternate periods of load and rest specified in the rating, the apparatus starting cold and for the total time specified in the rating without causing any of the specified limitations to be exceeded.*

Power Resistor:

a resistor capable of dissipating 5 watts or more.

Power:

the time rate of transferring or transforming energy; the rate of doing work or expending energy.

Rating:

a designated limit of operating characteristics of a machine, apparatus or device, based on definite conditions.

Note 1: Such operating characteristics as load, voltage, frequency, etc., may be given in the rating.

Note 2: The rating of control apparatus in general is expressed in volts, amperes, horsepower or kilowatts as may be appropriate, except that resistors are rated in ohms, amperes and class of service.*

Reactor:

a device used for introducing reactance into a circuit for purposes such as motor starting, paralleling transformers and control of current.*

Rectifier:

Resistance Method of Temperature Determination:

this method consists in the determination of temperature by comparison of the resistance of the winding at the temperature to be determined with the resistance at a known temperature.**

Resistance Tolerance:

the resistance tolerance of a power resistor is the extent to which its resistance may be permitted to deviate above or below the specified resistance. resistance tolerance is usually expressed in percent.

Resistance:

Resistive Conductor:

Resistivity:

the resistivity of a material is the resistance of a sample of the material having specified dimensions.

Resistor Core:

the resistor core or base of a power resistor is the insulating support on which the resistive conductor is wound.

Resistor:

a device, the primary purpose of which is to introduce resistance into an electric circuit.*

Rheostat:

an adjustable resistor so constructed that its resistance may be changed without opening the circuit in which it may be connected.*

Screw-Base Resistor:

a power-type resistor equipped with edison-type screw-base terminals for quick interchangeability.

Short-Time Rating:

the rating that defines the load which can be carried for a short and definitely specified time, the machine, apparatus or device being at approximately room temperature at the time the load is applied.*

Silicone:

a silicone coating meeting mil-r-26 used on power type wirewound resistors.

Single-Wound Resistor:

a resistor that has only one layer of resistance wire or ribbon wound around the insulating base or core.

Slim Mox:

a flat style resistor ohmite manufactures. they are available in a variety of sizes and values.

Stackohm®†:

Still Air:

still air is considered air having no circulation except that created by the heat of the resistor which is being operated.

Tapped Resistor:

a resistor with two or more steps.

Temperature Coefficient of Resistance:

a measure of the increase or decrease in resistance of a resistive conductor due to change in temperature in parts per million (ppm). rt = rr + [rr(αt – αtr)] where, rt = resistance of conductor at temperature t rr = resistance of conductor at reference temperature tr α = temperature coefficient of resistance at reference temperature tr

Temperature Rise:

temperature rise is the difference in temperature between the initial and final temperature of a resistor. temperature rise is expressed in degrees c or f, usually referred to an ambient temperature. temperature rise equals the hot spot temperature minus the ambient temperature.

Thermal Shock:

thermal shock consists of a sudden marked change in the temperature of the medium in which the device operates.

Thermocouple:

a device for converting heat energy into electrical energy consisting of a pair of dissimilar conductors so joined as to produce a thermo-electric effect. it is used with a millivoltmeter to measure temperature rise in apparatus.

Thermometer Method of Temperature Determination:

this method consists in the determination of the temperature by a mercury or alcohol thermometer, by a resistance thermometer, or by a thermocouple, any of these instruments being applied to the hottest part of the apparatus accessible to a mercury or alcohol thermometer.**

Tolerance (%):

the tolerance is the allowable deviation from teh nominal resistance value.

Varying Duty:

Voltage (V or E):

Voltage Coefficient (VCR):

Watt:

a unit of electric power. it is the power expended when one ampere of direct current flows through a resistor of one ohm.

Winding Pitch:

the distance from any point on a turn of a resistive conductor to the corresponding point on an adjacent turn measured parallel to the long axis of the winding.

Notes:
* ASA Standard
** NEMA Standard