Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

node analysis
a circuit analysis technique in which KCL is used to determine the node voltages in a network.
nominal voltage
a number given to a system to name its classification of voltage, such as rated values.
non-time delay fuse

See single-element fuse
non-transposition
refers to a three-phase electric power transmission line whose conductors are not transposed See transposition.
normal demagnetization curve
the second quadrant portion of the hysteresis loop generated when magnetic induction (B)is plotted against applied field (H ), which is mathematically related to the intrinsic curve; used to determine the performance of a magnet in a magnetic circuit.
normally closed contact
contact of a contactor that is closed when the coil of the contactor is deenergized and opened when the coil is energized.
normally closed, time to close
a relay that is closed when the power to its actuator is off, but has a time delay to close when power is removed from the actuator. When power is applied, the relay immediately opens.
normally open contact
a contact that is open under normal operating conditions and closes when an action is initiated in its controller. For a contact that is part of a relay, the contact remains open when the relay is deenergized and closes when the relay is energized.
normally open, time to close a time delay
relay that is open when the power to its actuator is off. When power is applied to the actuator, the relay remains open for an adjustable time delay, after which it closes. When power is removed from the actuator, the relay opens immediately.
Norton theorem
states that the voltage across an element that is connected to two terminals of a linear, bilateral network is equal to the short-circuit current between these terminals in the absence of the element, divided by the admittance of the network looking back from the terminals into the network, with all generators replaced by their internal admittances.
notch
a disturbance of the normal voltage waveform of duration less than 0.5 cycles, is of a polarity that is opposite to the waveform and is hence subtracted from the normal waveform with respect to the peak value of the disturbance voltage.
NTSC

See National Television System Committee
nuclear magnetic resonance
the phenomenon in which the resonant frequency of nuclear spin is proportional to the frequency of an applied magnetic field.
See magnetic resonance imaging
nuclear power plant
a thermal electric power plant in which the heat for steam turbines is produced by nuclear fission.
nuclear reaction
a reaction which causes changes in the nucleus of an atom, thus changing elements to another element or isotope, usually with the release of energy.
nuclear reactor
(1) an apparatus designed to facilitate, contain, and control a nuclear chain reaction.

(2) any heat-producing array of fissile radioactive materials constructed so as to produce a controlled chain-reaction.
null a point on the radiation pattern that corresponds to zero or minimum values.
ODP

See open drip-proof
Oersted
Oersted, Hans Christian (1777-1851) Born: Rudkobing, Langeland, Denmark

is best known as the discoverer of electromagnetism. Oersted was a strong teacher and did much to bring Danish science up to world-class standards. Oersted predicted the magnetic effect of electric current in 1813, but was unable to prove it until 1820. The publication of his results spurred the work of Faraday and Ampere. Oerstad went on to make other contributions in other sciences. He did not, however, return to his study of electricity.
off-axis illumination
illumination that has no on-axis component, i.e., that has no light which is normally incident on the mask. Examples of off-axis illumination include annular and quadrupole illumination.
Ohm's Law
a fundamental law which states that the voltage across a resistance is directly proportional to the current flowing through it. The constant of proportionality is known as the resistance.

This concept can be generalized to include the relationship between the voltage and current in all situations, including alternating voltages and currents. In this case, all the quantities are measured as complex numbers, known as phasors, that are functions of frequency. This broadens the basic definition of resistance, which is a real number measured in ohms, to that of impedance, which is a complex number with magnitude measured in ohms and phase angle in degrees. The real part of the complex number representing impedance is the resistance while the imaginary part is the reactance. Ohm's Law is a central concept to most electrical engineering theories.
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