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
A
Accent Lighting - Directional lighting to emphasize a
particular object or draw attention to a part of the field
of view.
Accessible - (As applied to wiring methods)
Capable of being removed or exposed without damaging the
building structure or finish, or not permanently closed in
by the structure or finish of the building.
Accessible - (as applied to equipment) Admitting
close approach: not guarded by locked doors, elevation, or
other effective means. (see
Accessible, Readily)
Accessible, Readily - (Readily Accessible) Capable of
being reached quickly for operation, renewal, or
inspections, without requiring those to whom ready access is
requisite to climb over or remove obstacles or to resort to
portable ladders, chairs, etc.
Ambient Temperature - The temperature of the air, water, or surrounding earth. Conductor ampacity
is corrected for changes in ambient temperature including
temperatures below 86°F. The cooling effect can increase the
current carrying capacity of the conductor. (Review Section
310-10 of the Electrical Code for more understanding)
Ammeter - An electric meter used to measure
current, calibrated in amperes.
Ampacity
- The current-carrying capacity of conductors or
equipment, expressed in amperes.
Ampere - The
basic unit measuring the quantity of electricity.
Anodizing - Any electrolytic or chemical process
by which a protective or decorative film is released on a
metal surface.
Apparent Power-The
product of voltage and current in a circuit.
Arc-Sparking that results when
undesirable current flows between two points of differing
potential. This may be due to leakage through the
intermediate insulation or a leakage path due to
contamination.
Armature Coil-A
winding that develops current output from a generator when
its turns cut a magnetic flux.
Arrester-A
nonlinear device to limit the amplitude of voltage on a
power line. The term implies that the device
stops
overvoltage problems (i.e.
lightning). In actuality, voltage clamp levels, response
times and installation determine how much voltage can be
removed by the operation of an arrester.
Asymmetric - Unequal distribution about one or
more axes.
Attenuation-The
reduction of a signal from one point to another. For an electrical surge, attenuation
refers to the reduction of an incoming surge by a limiter
(attenuator). Wire resistance, arresters,
power conditioners attenuate surges to varying degrees.
AWG-American
Wire Gage.
This term refers to the U.S. standard for wire size.
Autotransformer-A transformer used to step voltage up
or down. The primary and secondary windings share common
turns, and it provides no isolation.
Auxiliary Source-A power source dedicated to providing emergency power to a critical load
when commercial power is interrupted.
Back
to the top
B
Ballast - An auxiliary electrical device for
fluorescent and other discharge light sources.
Bonding Jumper - A bare or insulated conductor used
to ensure the required electrical conductivity between metal
parts required to be electrically connected. Frequently used
from a bonding bushing to the service equipment enclosure to
provide a path around concentric knockouts in an enclosure
wall: also used to bond one raceway to another.
BTU-British
Thermal Unit.
Energy required to raise one
pound of water one degree Fahrenheit. One pound of water at
32 degrees F requires the transfer of 144 BTUs to freeze
into solid ice.
Buck-Boost Transformer-A small, low voltage transformer
placed in series with the power line to increase or reduce
steady state voltage.
Busbar-A
heavy, rigid conductor used for high voltage feeders.
Back
to the top
C
Candlepower (or Candela) - Basic unit for measuring luminous intensity from a light
source in a given direction.
Coefficient of
Utilization
- The amount of light (lumens) delivered in a workplace as
a percent of the rated lumens of the lamp.
Cold Cathode Lamp - An electric-discharge lamp whose
mode of operation is that of a glow discharge (Neon Lights).
Common Mode (CM)-The term refers to electrical
interference which is measurable as a ground referenced
signal. In true common mode a signal is common to both the
current carrying conductors.
Common Node Noise-An undesirable voltage which appears between the power conductors and
ground.
Conduit-A
tubular raceway for data or power cables. Metallic conduit is common, although non-metallic
forms may also be used. A conduit may also be a path or duct
and need to be tubular.
Continuity - The state of being whole, unbroken.
Continuous Load
- A load where the maximum current is expected to continue
for three hours or more.
Rating of the branch circuit protection device shall not
be less tan 125% of the continuous load.
Current-The
movement of electrons through a conductor. Measured in amperes and its symbol is "I".
Current Transformer-(or
CT)
- A transformer used in instrumentation to assist in
measuring current. It utilizes the strength of the magnetic
field around the conductor to form an induced current that
can then be applied across a resistance to form a
proportional voltage.
Back
to the top
D
Demand Factor - For an electrical system or feeder
circuit, this is a ratio of the amount of connected load (in
kV or amperes) that will be operating at the same time to
the total amount of connected load on the circuit. An 80%
demand factor, for instance, indicates that only 80% of the
connected load on a circuit will ever be operating at the
same time. Conductor capacity can be based on that amount of
load.
Dropout-A
discrete voltage loss. A voltage sag (complete or partial) for a very
short period of time (milliseconds) constitutes a dropout
Dustproof - Constructed or protected so that
dust will not interfere with its successful operation.
Dust-tight - Constructed so that dust will not
enter the enclosing case under specified test conditions.
Duty, continuous - A service requirement that demands
operation at a substantially constant load for an
indefinitely long time.
Duty, intermittent - A service requirement that demands
operation for alternate intervals of load and no load, load
and rest, or load, no load, and rest.
Duty, periodic - A type of intermittent duty in
which the load conditions regularly reoccur.
Duty, short time - A requirement of service that
demands operations at a substantially constant load for a
short and definitely specified time.
Duty, varying - A requirement of service that
demands operation at loads, and for intervals of time, both
of which may be subject to wide variation.
Back
to the top
E
Earth Ground-A
low impedance path to earth for the purpose of discharging
lightning, static, and radiated energy, and to maintain the
main service entrance at earth potential.
Efficiency-The
percentage of input power available for used by the load. The mathematical formula is: Efficiency = P o/ Pi
Where "Po" equals
power output, "Pi"
equals power input, and power is represented by watts.
Electrical Degrees-One cycle of AC. power is divided into
360 degrees. This allows mathematical relationships between
the various aspects of electricity.
Also, what the mothers of many liberal arts majors
wish their daughters had married (or vice-versa)
Electromagnetic-A
magnetic field cause by an electric current. Power lines cause electromagnetic
fields which can interfere with nearby data cables.
Electromechanical-A mechanical device which is controlled by an electric device. Solenoids and shunt trip circuit
breakers are examples of electromechanical devices.
Electrostatic-A
Potential difference (electric charge) measurable between
two points which is caused by the distribution if dissimilar
static charge along the points. The voltage level is usually in
kilovolts (volts times 1000).
EMF-Electromotive force or voltage
EMI, RFI-Acronyms for various types of
electrical interference: electromagnetic interference, radio
frequency interference.
ESD-Electrostatic Discharge (static
electricity). The effects of static discharge can range from
simple skin irritation for an individual to degraded or
destroyed semiconductor junctions for an electronic device.
Explosion-proof
- Designed and constructed to withstand and internal
explosion without creating an external explosion or fire.
Back
to the top
F
Feeder - A circuit, such as conductors in
conduit or a busway run, which
carries a large block of power from the service equipment to
a sub-feeder panel or a branch circuit panel or to some
point at which the block power is broken into smaller
circuits.
Ferroresonance-Resonance resulting when the iron
core of an inductive component of an LC circuit is saturated, increasing the
inductive reactance with respect to the capacitance
reactance.
Ferroresonant Transformer-A voltage regulating transformer
which depends on core saturation and output capacitance.
Filter Frequency Range
-The
frequency range within which the filter operates.
Flashover-Flashing
due to high current flowing between two points of different
potential. Usually due to
insulation breakdown resulting from arcing.
Fluctuation-A surge or sag in voltage amplitude,
often caused by load switching or fault clearing.
Flux-The lines
of force of a magnetic field.
Forward Transfer
Impedance-The
amount of impedance placed between the source and load with
installation of a power conditioner. With no power
conditioner, the full utility power is delivered to the
load; even a transformer adds some opposition to the
transfer of power. On transformer based power conditioners,
a high forward transfer impedance limits the amount
of inrush current available to the load.
Frequency (Noise) Attenuation - The
range of attenuation (limiting) for a given frequency range.
In this case, the greater the negative number, the more
noise reduction.
Back
to the top
G
Ground - A large conducting body (as the
earth) used as a common return for an electric circuit and
as an arbitrary zero of potential.
Grounded, effectively - Intentionally connected to earth
through a ground connection or connections of sufficiently
low impedance and having sufficient current-carrying
capacity to prevent the buildup of voltages that may result
in undue hazards to connect equipment or to persons.
Grounded Conductor - A system or circuit conductor that
is intentionally grounded, usually gray or white in color.
Grounding Conductor - A conductor used to connect metal
equipment enclosures and/or the system grounded conductor to
a grounding electrode, such as the ground wire run to the
water pipe at a service; also may be a bare or insulated
conductor used to ground motor frames, panel boxes, and
other metal equipment enclosures used throughout electrical
systems. In most conduit systems, the conduit is used as the
ground conductor.
Grounding Equipment Conductor - The conductor used to connect the non-current-carrying
metal parts of equipment, raceways, and other enclosures to
the system grounded conductor, the grounding electrode
conductor, or both, of the circuit at the service equipment
or at the source of a separately derived system.
Grounding Electrode - The conductor used to connect the
grounding electrode to the equipment-grounding conductor, to
the grounded conductor, or to both, of the circuit at the
service equipment or at the source of a separately derived
system.
Ground Fault Circuit
Interrupter
- A device intended for the protection of personal that
functions to de-energize a circuit or portion thereof within
an established period of time when a current to ground
exceeds some predetermined value that is less than required
to operate the overcurrent
protection device of the supply circuit.
Ground Fault Protection
of Equipment
- A system intended to provide protection of equipment
from damaging line to ground fault currents by operating to
cause a disconnecting means to open all ungrounded
conductors of the faulted circuit. This protection is
provided at current levels less than those required to
protect conductors from damage through the operations of a
supply circuit overcurrent
device.
Back
to the top
H
High Intensity Discharge
Lamps (HID.)
- A general group of lamps consisting of mercury, metal
halide, high-pressure sodium, and low pressure sodium lamps.
High-pressure Sodium
Lamps
- A sodium vapor in which the partial pressure of the
vapor during operation is the order of 0.1 atmospheres.
Hot Cathode Lamp - An electrical discharge lamp whose mode of operation is that of an arc
discharge.
Back
to the top
I
Impedance-Forces
which resist current flow in AC circuits, i.e. resistance,
inductive reactance, capacitive reactance.
Inductance-The
ability of a coil to store energy and oppose changes in
current flowing through it.
A function of the cross sectional area, number of turns of coil,
length of coil and core material.
Input Power Frequency
- This
is the frequency range that can be input into the suppressor
without damaging it.
In Sight From - (within sight from, within sight)
Where this Code specifies that one equipment shall be "in
sight from", "within sight from" or "within sight", etc. of
another equipment, the specified equipment is to be visible
and not more that 50'
distant from the other.
Interrupter Rating - The highest current at rated
voltage that a device is intended to interrupt under
standard test conditions.
Back
to the top
J
Joule - A measure of the amount of energy
delivered by one watt of power in one second, or 1 million
watts of power in one microsecond. The joule rating of a
surge protection device is the amount of energy that it can
absorb before it becomes damaged. In comparing surge
protection performance, the Joule rating of a surge
suppressor is less important than the let-through voltage
rating. This reflects the fact that surge suppressors may
protect equipment by deflecting surges as well as absorbing
them. There is no standard for measuring the joule rating of
surge suppressors which has resulted in wildly exaggerated
claims by unscrupulous vendors.
Back
to the top
K
Kilo--(K)- -A
metric prefix meaning 1000 or 10 to the 3rd power.
KVA-(Kilovolt amperes) (volts times
amperes) divided by 1000. 1 KVA=1000 VA. KVA is actual
measured power (apparent power) and is used for circuit
sizing.
KW-(Kilowatts)
watts divided by 1000. KW is real power and is important in sizing Uninterruptible Power
Supplies, motor generators or other power conditioners. See
also "power factor".
KWH-(Kilowatt
hours) KW times hours. A measurement of power and time used by utilities for
billing purposes.
Back
to the top
L
Labeled - Items to which a label, trademark,
or other identifying mark of nationally recognized testing
labs has been attached to identify the items as having been
tested and meeting appropriate standards.
Lagging Load-An
inductive load with current lagging voltage. Since inductors tend to resist
changes in current, the current flow through an inductive
circuit will lag behind the voltage. The number of
electrical degrees between voltage and current is known as
the "phase angle". The cosine of this angle is equal to the
power factor (linear loads only).
LC Circuit-An electrical network containing both
inductive and capacitive elements.
Leading Load-A
capacitive load with current leading voltage. Since capacitors resist changes in
voltage, the current flow in a capacitive circuit will lead
the voltage.
Linear Load-A load in which the current
relationship to voltage is constant based on
a relatively
constant load impedance.
Line Conditioner - This term isn't used consistently,
therefore its meaning has been blurred. The term is
sometimes used to describe equipment that provides some type
of filtering or Regulation to an AC power source and may be
any of the following devices: Surge Suppressor, Ferroresonant Transformer, AC Filter or Tap Changing
Regulator.
Line Imbalance-Unequal loads on the phase lines of a
multiphase feeder.
Listed - Equipment or materials included in
a list published by an organization acceptable to the
authority having jurisdiction and concerned with product
evaluation, that maintains periodic inspection of production
of listed equipment or materials, and whose listing states
either that the equipment or material meets appropriate
designated standards or has been tested and found suitable
for use in specified manner.
Load-The driven device that uses the power
supplied from the source.
Load Balancing-Switching the various loads on a
multi-phase feeder to equalize the current in each line.
Load Fault-A malfunction that causes the load to
demand abnormally high amounts of current from the source.
Load Regulation-A term used to describe the effects
of low forward transfer
impedance. A power conditioner with "load regulation"
may not have voltage regulation. Removing the power
conditioner altogether will improve load regulation.
Load Switching-Transferring the load from one source
to another.
Load Unbalance-Unequal loads on the phase lines of a
multi- phase system.
Location, damp - A location subject to moderate
amount of moisture such as some basements, barns, cold
storage, warehouse and the like.
Location, dry - A location not normally subject to
dampness or wetness: a location classified as dry may be
temporarily subject to dampness or wetness, as in case of a
building under construction.
Location, wet - A location subject to saturation
with water or other liquids.
Back
to the top
M
Maximum Operating
Voltage - This
is the maximum 50 to 60 Hz AC voltage the unit can sustain
without damage or failure of the suppressor.
Measured Limiting (used
to be known as "let-through") Voltage - This
is the maximum voltage measured across the terminals of the
suppressor during the time the testing voltages were applied
to the unit..
Mega--(M)--A metric prefix meaning 1,000,000 or
10 to the 6th power.
Megger
- A test instrument for measuring the insulation
resistance of conductors and other electrical equipment;
specifically, a mega-ohm (million ohms) meter; this is a
registered trademark of the James Biddle Co.
Mega-ohm - A unit of electrical resistance
equal to one million ohms.
Mega-ohmmeter
- An instrument for measuring extremely high resistance.
Megger
- A test instrument for measuring the insulation
resistance of conductors and other electrical equipment;
specifically, a mega-ohm (million ohms) meter; this is a
registered trademark of the James Biddle Co.
Mercury Lamps - An electric discharge lamp in which
the major portion of the radiation is produced by the
excitation of mercury atoms.
Metal Halide Lamps - A discharge lamp in which the light
is produced by the radiation from the mixture of metallic
vapor and the products of disassociation.
Metal Oxide Varistor-(MOV)-A MOV is a voltage sensitive breakdown device which is
commonly used to limit overvoltage
conditions (electrical surges) on power and data lines. When
the applied voltage exceeds the breakdown point, the
resistance of the MOV decreases from a very high level
(thousands of ohms) to a very low level (a few ohms). The
actual resistance of the device is a function of the rate of
applied voltage and current.
Micro--(U)-A metric prefix meaning one millionth of a unit or 10-6.
Micron-A
metric term meaning one millionth of a meter.
Milli--(m)-A metric prefix meaning one
thousandth of a unit or 10-3
Motor, Shunt- Wound - This type of motor runs practically
constant speed, regardless of the load. It is the type
generally used in commercial practice and is usually
recommended where starting conditions are not usually
severe. Speed of the shunt-wound motors may be regulated in
two ways: first, by inserting resistance in series with the
armature, thus decreasing speed: and second, by inserting
resistance in the field circuit, the speed will vary with
each change in load: in the latter, the
speeds is
practically constant for any setting of the controller.
This latter is the most generally used for adjustable-speed
service, as in the case of machine tools.
Motor, DC, Series- Wound
- This type of motor speed varies automatically with the
load, increasing as the load decreases. Use of sbe started without load, since they
will race to a dangerous degree.
Motor, DC, Compound-
Wound
- A combination of the shunt wound and series wound type,
which combines the characteristics of both. Varying the
combination of the two windings may vary characteristics.
These motors are generally used where severe starting
conditions are met and constant speed is required at the
same time.
Motor,
Squirrel-Cage-Induction - The most simple and reliable of all electric motors. Essentially a constant speed machine, which is adaptable for users
under all but the most severe starting conditions.
Requires little attention as there is no
commutator
or slip rings, yet operates with good efficiency.
Motor, Wound-Rotor (Slip Ring) Induction - Used for constant speed-service
requiring a heavier starting torque than is obtainable with
squirrel cage type. Because of its lower starting
current, this type is frequently used instead of the
squirrel-cage type in larger sizes. These motors are also
used for varying-speed-service. Speed varies with this load,
so that they should not be used where constant speed at each
adjustment is required, as for machine tools.
Motor, Single-Phase
Induction
- This motor is used mostly in small sizes, where
polyphase
current is not available. Characteristics are not as good
as the polyphase motor and for size larger that 10 HP, the line
disturbance is likely to be objectionable. These motors are
commonly used for light starting and for running loads up to
1/3 HP Capacitor and repulsion types provide greater torque
and are built in sizes up to 10 HP.
Motor, Synchronous - Run at constant speed fixed by
frequency of the system. Require direct current for
excitation and have low starting torque. For large
motor-generators sets, frequency changes, air compressors
and similar apparatus which permits starting under a light
load, for which they are generally used. These motors are
used with considerable advantage, particularly on large
power systems, because of their inherent ability to improve
the power factor of the system.
MTBF-(Mean Time Between
Failure) the probable length of time that a component
taken from a particular batch will survive if operated under
the same conditions as a sample from the same batch.
Back
to the top
N
Nano--(n)-A metric
prefix meaning one billionth of a unit or 10-9.
NEMA-National
Electrical Manufacturers Association.
NEC-National
Electrical Code.
Neutral-The grounded junction point of the
legs of a wye circuit. Or, the
grounded center point of one coil of a delta transformer
secondary. Measuring the phase to neutral voltage of each of
the normal three phases will show whether the system is wye or delta. On a wye system, the
phase to neutral voltages will be approximately equal and
will measure phase to phase voltage divided by 1.73. On a
center tapped delta system, one phase to neutral voltage
will be significantly higher than the other two. This higher
phase is often called the "high leg".
Neutralizing Winding-An extra winding used to cancel
harmonics developed in a saturated secondary winding,
resulting in a sinusoidal output waveform from a
ferroresonant
transformer.
Nominal Voltage-The
normal or designed voltage level. For three phase wye systems,
nominal voltages are 480/277 (600/346 Canada) and 208/120 where the first number
expresses phase to phase ( or line
to line) voltages and the second number is the phase to
neutral voltage. The nominal voltage for most single phase
systems is 240/120.
Non-inductive Circuit - A circuit in which the magnetic
effect of the current flowing has been reduced by one
several methods to a minimum or to zero.
Non-linear Load - A load where the wave shape of the
steady state current does not follow the wave shape of the
applied voltage.
Back
to the top
O
Ohm - The derived unit for electrical
resistance or impedance; one ohm equals one volt per ampere.
Ohmmeter - an instrument for measuring
resistance in ohms. Take a look at this diagram to see how
an ohmmeter is used to check a small control transformer.
The ohmmeter's pointer deflection is controlled by the
amount of battery current passing through the moving coil.
Before measuring the resistance of an unknown resistor or
electrical circuit, the ohmmeter must first be calibrated.
If the value of resistance to be measured can be estimated
within reasonable limits, a range selected that will give
approximately half-scale deflection when the resistance is
inserted between the probes. If the resistance is unknown,
the selector switch is set on the highest scale. Whatever
range is selected, the meter must be calibrated to read zero
before the unknown resistance is measured.
Overcurrent - Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short
circuit or ground fault.
Overload - Load greater than the load for
which the system or mechanism was intended. A fault, such as
a short circuit or ground fault, is not an overload.
Back
to the top
P
Panelboard - A single panel or group of panel units designed for assembly in the
form of a single panel: includes buses and may come with or
without switches and/or automatic
overcurrent
protective devices for the control of light, heat, or
power circuits of individual as well as aggregate capacity.
It is designed to be placed in a cabinet or cutout box that
is in or against a wall or partition and is accessible only
from the front.
Peak Surge Current
- The
maximum current allowed for a single impulse with continuous
voltage applied.
Plenum - Chamber or space forming a part of
an air conditioning system
Power-Electrical energy measured according
to voltage and current (normally watts). Power in watts
equals volts times amperes for DC circuits. For single phase AC circuits,
watts equal volts times amperes
times power factor.
Power Factor-Watts divided by
voltamps
(VA), KW divided by KVA. Power factor: leading and lagging
of voltage versus current caused by inductive or capacitive
loads, and 2) harmonic power factor: from nonlinear current.
Propagation-The
travel of an electrical waveform along a medium. In other words, a
surge passing along a power cord to a system.
Protector-A protector is another name for an
arrester or diverter.
Back
to the top
R
Rainproof - So constructed, projected, or
treated as to prevent rain from interfering with the
successful operation of the apparatus under specified test
conditions.
Rain-tight - So constructed or protected that
exposure to a beating rain will not result in the entrance
of water.
Real Power-Watts.
Reactance-Opposition
to the flow of alternating current. Capacitive reactance is the opposition offered by capacitor,
and inductive reactance is the opposition offered by a coil
or other inductance.
Recloser-The automatic closing of a
circuit-interrupting device following automatic tripping.
Rectifier-An electrical device used to change
AC power into DC power. A battery charger is a rectifier.
Redundancy-The
inclusion of additional assemblies and circuits (as within a
UPS) with provision for automatic switchover from a failing
assembly or circuit to its backup counterpart.
Reflection-The return wave generated when a
traveling wave reaches a load, a source, or a junction where
there is a change in line impedance.
Reliability-The
statistical probability of trouble-free operation of a given
component or assembly.
Used principally as a function of MTBF (Mean Time
Before
Failure) and MTTR (Mean Time to Repair).
RFI-Radio
Frequency Interference.
Ride through-The ability of a power conditioner to
supply output power when input power is lost.
RMS-(Root mean square)-
used for AC voltage and current values. It is the square
root of the average of the squares of all the instantaneous
amplitudes occurring during one cycle. RMS is called the
effective value of AC because it is the value of AC voltage
or current that will cause the same amount of head to be
produced in a circuit containing only resistance that would
be caused by a DC voltage or current of the same value. In a
pure sine wave the RMS value is equivalent to .707 times the
peak value and the peak value is 1.414 times the RMS value.
The normal home wall outlet which supplies 120 volts RMS has
a peak voltage of 169.7 volts.
Back
to the top
S
Separately Derived
System
- A premises wiring system whose power is derived from a
battery, a solar photovoltaic system, or from a generator,
transformer, or converter windings, and that has no direct
electrical connection, including solidly connected grounded
circuit conductor, to supply conductors originating in
another system.
Service Drop - Run of cables from the power
company's aerial power lines to the point of connection to a
customer's premises.
Service Conductors - The supply conductors that extend
from the street main or transformers to the service
equipment of the premises being supplied
Service Entrance
Conductors
- (Overhead) The service conductors between the terminals
of the service equipment and a point usually outside the
building, clear of building walls, where joined by tap or
splice to the service drop.
Service Entrance
Conductors
- (Underground) The service
conductors between the terminals of the service equipment
and the point of connection to the service lateral.
Service Equipment - The necessary equipment, usually
consisting of a circuit breaker or switch and fuses and
their accessories, located near the point entrance of supply
conductors to a building and intended to constitute the main
control and cutoff means for the supply to the building.
Service Lateral - The underground service conductors
between the street main, including any risers at a pole or
other structure or from transformers, and the first point of
connection to the service-entrance conductors in a terminal
box, meter, or other enclosure with adequate space, inside
or outside the building wall. Where there is no terminal
box, meter, or other enclosure with adequate space, the
point of connection is the entrance point of the service
conductors into the building.
Service Point - The point of connection between the
facilities of the serving utility and the premises wiring.
Surge-A short
duration high voltage condition. A surge lasts for several cycles where a transient lasts
less than one half cycle.
Often confused with "transient".
Switchboard - A large single panel, frame, or
assembly of panels having switches,
overcurrent, and other protective devices, buses, and
usually instruments mounted on the face or back or both.
Switchboards are generally accessible from the rear and from
the front and are not intended to be installed in cabinets.
Switch, general use - A switch intended for use in
general distribution and branch circuits. It is rated in
amperes and is capable of interrupting its rated voltage.
Switch, general-use snap
- A type of general-use switch so constructed that it can
be installed in flush device boxes or on outlet covers, or
otherwise used in conjunction with wiring systems recognized
by the National Electric Code.
Switch, isolating - A switch intended for isolating an
electrical circuit from the source of power. It has no
interrupting rating and is intended to be operated only
after the circuit has been opened by some other means.
Switch, knife - A switch in which the circuit is
closed by a moving blade engaging contact clips.
Switch, motor-circuit - A switch, rated in horsepower,
capable of interrupting the maximum operating overload
current of a motor of the same horsepower rating as the
switch at the rated voltage.
Switch, transfer - A transfer switch is an automatic or
non-automatic device for transferring one or more load
conductor connections from one power source to another.
Switch-Leg - That part of a circuit run from a
lighting outlet box where a luminaire
or lamp-holder is installed down to an outlet box that
contains the wall switch that turns the light or other load
on or off: it is a control leg of the branch circuit.
Back
to the top
T
Tap Changing Regulator
- a device that improves the
regulation of an AC power source. The regulator is placed
between an AC power source and the load to be protected. A
tap-changing regulator has a special transformer with
multiple outputs or taps. Typically, one of the output taps
provides a voltage equal to the input voltage, while other
taps provide various voltages which are a few percent higher
or lower than the input voltage. An automatic selector
switch chooses the tap which provides the voltage closest to
the desired output voltage. In operation, if the AC power
source were to suddenly decrease in voltage by 5% from
nominal and remain at that voltage, then the Tap-Changing
Regulator would respond by choosing a transformer tap 5%
higher than the input voltage and would supply this
corrected voltage to the load. Tap-Changing Regulators are
especially useful in situations where a site is experiencing
chronically high or low line voltage.
Three-Phase Power-Three separate outputs from a single
source with a phase differential of 120 electrical degrees
between any two adjacent voltages or currents. Mathematical
calculations with three phase power must allow for the
additional power delivered by the third phase. Remember,
both single phase and three phase
have the same phase to phase voltages, therefore you must
utilize the square root of 3 in your calculations. For
example, KVA equals volts times
amps for DC and for single phase. For three
phase
the formula is volts times the square root of three times
amps.
Total Harmonic
Distortion (THD)-The
square root of the sum of the squares of the RMS harmonic
voltages or currents divided by the RMS fundamental voltage
or current. Can also be calculated in the
same way for only even harmonics or odd harmonics.
Transformer-A static electrical device which , by electromagnetic induction, regenerates AC power
from one circuit into another. Transformers are also used to
change voltage from one level to another. This is
accomplished by the ratio of turns on the primary to turns
on the secondary (turns ratio). If the primary windings have
twice the number of windings as the secondary, the secondary
voltage will be half of the primary voltage.
Transient-A high amplitude, short duration
pulse superimposed on the normal voltage wave form or ground
line.
Transient Response-The ability of a power conditioner to respond to a change. Transient step load response is the
ability of a power conditioner to maintain a constant output
voltage when sudden load (current) changes are made.
Transmission Line-The conductors used to carry
electrical energy from one location to another.
Transverse Mode Noise-(Normal mode)-
An undesirable voltage which appears from line to line of
a power line.
Back
to the top
U
UL 1449 - a UL
(UNDERWRITER'S LABORATORIES) safety specification that
surge suppression products are tested against. This specification includes a
requirement that surge suppression devices be marked with
the surge let-through voltage for a specific UL test
UL Approved - This is a widely used term which is
technically not correct. The correct terms are UL Listed or UL Recognized.
UL Listed - UL grants this form of approval to
equipment that will be user installed or operated and that
is found to meet the safety requirements of the applicable
UL standards. If a product is UL Listed, then it must be
marked with the UL insignia.
UL Recognized
- This is a form of formal approval granted by UL to
devices that are not used as free standing equipment on
their own, but are to be installed into some other system by
a manufacturer, electrician, or possibly by an end user.
Examples of UL Recognized equipment are wall switches, wire
connectors, wires, fuses, and circuit breakers. (See also
UL Listed above).
Back
to the top
V
VAC-Volts of
alternating current.
VDC-Volts of
direct current.
Volt (V)-The unit of voltage or potential
difference.
Voltage Drop -
The loss of voltage between the input to a device and the
output from a device due to the internal impedance or
resistance of the device. In all electrical systems, the
conductors should be sized so that the voltage drop never
exceeds 3% for power, heating, and lighting loads or
combinations of these. Furthermore, the maximum total
voltage drop for conductors for feeders and branch circuits
combined should never exceed 5%.
VOM-Volt
ohm-meter.
Voltage-Electrical
pressure, the force which causes current to flow through a
conductor. Voltage must be expressed as a
difference of potential between two points since it is a
relational term. Connecting both voltmeter leads to the same
point will show no voltage present although the voltage
between that point and ground may be hundred or thousands of
volts. This is why most nominal voltages are expressed as
"phase to phase" or "phase to neutral". The unit of
measurement is "volts". The electrical symbol is "e".
Back
to the top
W
WATT (W)-The unit of power. Equal to one joule
per second
Watertight - So constructed that water/moisture
will not enter the enclosure under specified test
conditions.
Weatherproof - So constructed or protected that
exposure to the weather will not interfere with successful
operation.
Back
to the top
Z
Zero Signal Reference-A connection point, bus, or conductor
used as one side of a signal circuit. It may or may not be
designated as ground. Is sometimes
referred to as circuit common.
