Thursday, March 19, 2009
Letter Z
Zener: It is used to make votahe stable at certain fix volt,it always operate under reverse bias condition
Letter W
Watt
The basic unit of electric power. The symbol for watt is “W.”
Word
Usually one or more bytes used to represent instructions or
data in digital equipment.
Wye
A connection arrangement used for the primary and/or
secondary of a three-phase transformer.
The basic unit of electric power. The symbol for watt is “W.”
Word
Usually one or more bytes used to represent instructions or
data in digital equipment.
Wye
A connection arrangement used for the primary and/or
secondary of a three-phase transformer.
Letter Vo
Volt
The basic unit of voltage. The symbol for volt is “V.”
Voltage
Also called difference of potential, electromotive force, or EMF.
Voltage is a force that, when applied to a conductor, causes
current to flow. Voltage is symbolized by “E” or “V” and is
measured in volts.
Voltmeter
A meter designed to measure voltage.
Volts per Hertz (V/Hz)Operation
Describes the operation of many variable frequency drives that
control the speed of an AC motor by varying the frequency of
the voltage applied to the motor while maintaining a constant
voltage to frequency ratio.
Letter V
Var
The basic unit for reactive power. Shortened from volt-ampere
reactive.
Variable Frequency Drive (VFD)An electronic device used to control the speed a of an AC
motor. A VFD controls the motor speed by varying the
frequency and voltage applied to the motor. Also called an AC
drive.
Variable Speed Drive An electronic drive device used to control the speed of an electric motor. This term applies to both AC Drives and DC
Drives.
Vector Control
A technique employed by some variable frequency drives that
involves calculations of AC motor current vectors and precise
control of motor flux to provide excellent speed and torque
control.
Letter Tr
Transformer
Coils of wire wound on a common frame that allow electrical
energy to be transferred from one circuit to another.
Transformers used in low frequency applications are commonly
wound around an iron core to improve energy transfer.
Transistor
A semiconductor device which usually has three terminals
although the names of the terminals are different for different
types of transistors. Some types of transistors are used as
electronic switches.
Trim
The front cover of a panelboard which includes an access door.
Trip Unit
The part of the circuit breaker that determines when the
breaker will trip. Many circuit breakers use a thermal-magnetic
or magnetic-only trip unit. Other circuit breakers have a solidstate
trip unit with multiple adjustments to custom fit the circuit
breaker’s time current curve to the application.
True Power
Also called real power, true power is the power dissipated by
circuit resistance. True power is equal to I2R and is measured in
watts. True power is also equal to the apparent power multiplied
by the power factor.
Coils of wire wound on a common frame that allow electrical
energy to be transferred from one circuit to another.
Transformers used in low frequency applications are commonly
wound around an iron core to improve energy transfer.
Transistor
A semiconductor device which usually has three terminals
although the names of the terminals are different for different
types of transistors. Some types of transistors are used as
electronic switches.
Trim
The front cover of a panelboard which includes an access door.
Trip Unit
The part of the circuit breaker that determines when the
breaker will trip. Many circuit breakers use a thermal-magnetic
or magnetic-only trip unit. Other circuit breakers have a solidstate
trip unit with multiple adjustments to custom fit the circuit
breaker’s time current curve to the application.
True Power
Also called real power, true power is the power dissipated by
circuit resistance. True power is equal to I2R and is measured in
watts. True power is also equal to the apparent power multiplied
by the power factor.
Letter Ti
Timing Relay
A control relay that incorporates a preset delay in contact
response. Some timing relays begin the time delay when the
relay is energized. Others begin the time delay when the relay
is de-energized.
Torque
A turning or twisting force. Since torque is expressed as a force
times the length of the radius at which the force is measured,
torque is represented in compound units such as pound-feet
(lb.-ft.)
Totally Enclosed Fan Cooled (TEFC )A motor enclosure type that restricts the flow of air into or out of the motor, but uses a fan to blow air over the
motor’s exterior.
Totally Enclosed Non-ventilated (TENV) A motor enclosure type that restricts the flow of air into or out of the motor. Because there are no ventilating openings, all
heat generated by the motor must be dissipated by conduction
through the encl
A control relay that incorporates a preset delay in contact
response. Some timing relays begin the time delay when the
relay is energized. Others begin the time delay when the relay
is de-energized.
Torque
A turning or twisting force. Since torque is expressed as a force
times the length of the radius at which the force is measured,
torque is represented in compound units such as pound-feet
(lb.-ft.)
Totally Enclosed Fan Cooled (TEFC )A motor enclosure type that restricts the flow of air into or out of the motor, but uses a fan to blow air over the
motor’s exterior.
Totally Enclosed Non-ventilated (TENV) A motor enclosure type that restricts the flow of air into or out of the motor. Because there are no ventilating openings, all
heat generated by the motor must be dissipated by conduction
through the encl
Letter T
Thermal-Magnetic
Used to describe a device that uses both heat and magnetism
as part of its operating principles. For example, a thermalmagnetic
circuit breaker can be tripped either by heat or
magnetic force resulting from an overcurrent.
Thermistor
A device used to sense temperature that varies in resistance as
temperature changes.
Thyristor
A family of multi-layer semiconductor devices that includes
silicon controlled rectifiers (SCR), gate turnoff (GTO) thyristors,
and other similar devices. Thyristors are often used in rectifier or
power switching circuits.
Time-Current Curve
A graph showing how long before a circuit breaker will trip at
each level of fault current.
Used to describe a device that uses both heat and magnetism
as part of its operating principles. For example, a thermalmagnetic
circuit breaker can be tripped either by heat or
magnetic force resulting from an overcurrent.
Thermistor
A device used to sense temperature that varies in resistance as
temperature changes.
Thyristor
A family of multi-layer semiconductor devices that includes
silicon controlled rectifiers (SCR), gate turnoff (GTO) thyristors,
and other similar devices. Thyristors are often used in rectifier or
power switching circuits.
Time-Current Curve
A graph showing how long before a circuit breaker will trip at
each level of fault current.
Letter Su
Step-up Transformer
A transformer with fewer turns of wire in its primary coil than
in its secondary coil. The step-up transformer is used to step up
the primary voltage to a higher secondary voltage.
Surge
An increase of at least ten percent in current and voltage that
typically lasts only a few microseconds.
Surge Protection Device (SPD)
A device designed to provide a degree of protection for
electrical equipment from the damaging effects of a surge. This
term applies to both secondary surge arresters and transient
voltage surge suppressors.
Switchboard
A large panel or assembly of panels containing switches,
overcurrent protective devices, buses, and associated
instruments. Unlike panelboards, switchboards sometimes
must be mounted away from a wall to allow access to rearmounted
equipment.
Switchgear
A coordinated design consisting of switching and interrupting
devices and associated equipment such as control and
protective devices and metering.
Synchronous Speed
The speed of the rotating magnetic field in a three-phase motor.
Synchronous speed is determined by the line frequency and the
number of motor poles.
..
A transformer with fewer turns of wire in its primary coil than
in its secondary coil. The step-up transformer is used to step up
the primary voltage to a higher secondary voltage.
Surge
An increase of at least ten percent in current and voltage that
typically lasts only a few microseconds.
Surge Protection Device (SPD)
A device designed to provide a degree of protection for
electrical equipment from the damaging effects of a surge. This
term applies to both secondary surge arresters and transient
voltage surge suppressors.
Switchboard
A large panel or assembly of panels containing switches,
overcurrent protective devices, buses, and associated
instruments. Unlike panelboards, switchboards sometimes
must be mounted away from a wall to allow access to rearmounted
equipment.
Switchgear
A coordinated design consisting of switching and interrupting
devices and associated equipment such as control and
protective devices and metering.
Synchronous Speed
The speed of the rotating magnetic field in a three-phase motor.
Synchronous speed is determined by the line frequency and the
number of motor poles.
..
Letter Sp
Speed-Torque Curve
A graphical representation of the torque provided by a motor
over a range of speeds.
Splice Plates, Splice Bars Plates or bars used to join the horizontal bus bars of adjoining switchboard or motor control center sections.
Starter Ratings
Motor Starters are rated according to size and type of load.
NEMA and IEC rate motor starters differently. IEC-rated devices
are rated according to maximum operational current. NEMA
specifies sizes from size 00 to size 9.
Stator
The stationary elements of the magnetic circuit of a rotating
machine such as a motor.
Step-down Transformer A transformer with more turns of wire in its primary coil than in
its secondary coil. The step-down transformer is used to step
down the primary voltage to a lower secondary voltage.
A graphical representation of the torque provided by a motor
over a range of speeds.
Splice Plates, Splice Bars Plates or bars used to join the horizontal bus bars of adjoining switchboard or motor control center sections.
Starter Ratings
Motor Starters are rated according to size and type of load.
NEMA and IEC rate motor starters differently. IEC-rated devices
are rated according to maximum operational current. NEMA
specifies sizes from size 00 to size 9.
Stator
The stationary elements of the magnetic circuit of a rotating
machine such as a motor.
Step-down Transformer A transformer with more turns of wire in its primary coil than in
its secondary coil. The step-down transformer is used to step
down the primary voltage to a lower secondary voltage.
Letter Sh
Short Circuit A normally unintended low resistance path for current.
Shunt Trip
A circuit breaker accessory used to remotely trip a circuit
breaker.
Single Quadrant Operation
Describes the operation of a variable speed drive that can
provide torque to drive the motor, but cannot provide braking
torque.
Slip
The difference between the synchronous speed of a threephase
induction motor and the rotor speed. Slip is often
expressed as a percentage.
Solid-State
Used to describe equipment that contains semiconductor
devices in an electronic circuit.
Shunt Trip
A circuit breaker accessory used to remotely trip a circuit
breaker.
Single Quadrant Operation
Describes the operation of a variable speed drive that can
provide torque to drive the motor, but cannot provide braking
torque.
Slip
The difference between the synchronous speed of a threephase
induction motor and the rotor speed. Slip is often
expressed as a percentage.
Solid-State
Used to describe equipment that contains semiconductor
devices in an electronic circuit.
Letter Se
Sensing Switch
A device, sometimes called a sensor, that turns on or off to
indicate presence or absence of an object or material. Examples
include limit switches and photoelectric , inductive, capacitive,
and sonar proximity switches.
Service Entrance
The place where power cables enter a building.
Service Factor
A numerical value that is multiplied by a motor’s rated
horsepower to determine the maximum horsepower at which
the motor should be operated.
Service Head
A device used to connect busway at the service entrance.
Service Section
The switchgear, switchboard, or power panelboard section
connected to incoming power.
Servo Drive
Usually refers to an electronic device used to control the speed
and torque of a servo motor as part of a closed-loop positioning
control system.
Letter S
Safety Switch
A type of enclosed switch that may also include provisions
for fuses. Single-throw safety switches are used to provide a
means for disconnecting power. Double-throw switches are
used to transfer loads from one power source to another or to
transfer power from one load to another.
Secondary Unit Substation
A coordinated design consisting of one or more transformers
mechanically and electrically linked to switchgear or
switchboard assemblies with an outgoing voltage rated below
1000 volts.
Selective Coordination
Applying circuit breakers in a manner that minimizes the extent
of an outage in the event of a fault. Circuit breakers are typically
installed in a branching arrangement. In the event of a fault, the
breaker electrically closest to the fault should trip first. This can
be accomplished by properly sizing and adjusting all breakers.
Selector Switch
A manual switch with multiple contact positions.
Semiconductor
A type of material, such as silicon, with more resistance than a
conductor, but less than that of an insulator. Semiconductors
can be manufactured to produce devices such as diodes,
transistors, thyristors, etc.
A type of enclosed switch that may also include provisions
for fuses. Single-throw safety switches are used to provide a
means for disconnecting power. Double-throw switches are
used to transfer loads from one power source to another or to
transfer power from one load to another.
Secondary Unit Substation
A coordinated design consisting of one or more transformers
mechanically and electrically linked to switchgear or
switchboard assemblies with an outgoing voltage rated below
1000 volts.
Selective Coordination
Applying circuit breakers in a manner that minimizes the extent
of an outage in the event of a fault. Circuit breakers are typically
installed in a branching arrangement. In the event of a fault, the
breaker electrically closest to the fault should trip first. This can
be accomplished by properly sizing and adjusting all breakers.
Selector Switch
A manual switch with multiple contact positions.
Semiconductor
A type of material, such as silicon, with more resistance than a
conductor, but less than that of an insulator. Semiconductors
can be manufactured to produce devices such as diodes,
transistors, thyristors, etc.
Letter Re
Reduced-Voltage Starter
A type of motor starter that applies less than the full-line
voltage to a three-phase induction motor while it is starting.
There are a variety of reduced-voltage starters. Some types
use electromechanical components and others use electronic
components. Electronic reduced voltage starters are often
referred to as solid-state reduced voltage starters or soft
starters.
Resistance
A property of a material or circuit that opposes current flow.
Resistance is symbolized by “R” and is measured in ohms.
Resistance Temperature Detector (RTD) A device used to sense temperature that varies in resistance as temperature changes.
A type of motor starter that applies less than the full-line
voltage to a three-phase induction motor while it is starting.
There are a variety of reduced-voltage starters. Some types
use electromechanical components and others use electronic
components. Electronic reduced voltage starters are often
referred to as solid-state reduced voltage starters or soft
starters.
Resistance
A property of a material or circuit that opposes current flow.
Resistance is symbolized by “R” and is measured in ohms.
Resistance Temperature Detector (RTD) A device used to sense temperature that varies in resistance as temperature changes.
Letter R
Random Access Memory (RAM)
Usually refers to a type of semiconductor memory often used
for temporary storage. RAM requires the continual application
of power to retain information. For some systems, battery
backup is used to prevent data or program loss in the event of a
power outage.
Reactance
The opposition to alternating current resulting from circuit
inductance and capacitance. The symbol for reactance is “X.”
The unit for reactance is the ohm.
Reactive Power
Power associated with inductance or capacitance. The unit for
reactive power is the var.
Read Only Memory (ROM)
Usually refers to a type of semiconductor memory often used
for permanent storage of data or programs that do not change.
Rectifier
A device or circuit that converts alternating current to direct
current.
Usually refers to a type of semiconductor memory often used
for temporary storage. RAM requires the continual application
of power to retain information. For some systems, battery
backup is used to prevent data or program loss in the event of a
power outage.
Reactance
The opposition to alternating current resulting from circuit
inductance and capacitance. The symbol for reactance is “X.”
The unit for reactance is the ohm.
Reactive Power
Power associated with inductance or capacitance. The unit for
reactive power is the var.
Read Only Memory (ROM)
Usually refers to a type of semiconductor memory often used
for permanent storage of data or programs that do not change.
Rectifier
A device or circuit that converts alternating current to direct
current.
Letter Pid
Programmable Logic Controller (PLC) A type of industrial computer used to control machines and processes. The PLC accepts inputs from switches and sensors
and uses these inputs together with other data and program
logic to control output devices.
Proportional-Integral-Derivative (PID) Control A closed-loop control technique that seeks to minimize error by
reacting to three values, one that is proportional to the error,
one that is representative of the error over time, and one that is
representative of the rate of change of the error.
Proximity Sensor
A type of sensing switch that detects the presence or absence
of an object without physical contact.
Pulse Width Modulation (PWM) As applied to variable frequency drives, this is a technique for
controlling the voltage applied to an AC motor by varying the
pulse width while also controlling the frequency of the pulses.
Pushbutton
A control device used to manually open and close a set of
contacts.
Letter Pl
PLC Scan
A complete execution cycle of a programmable logic controller.
The PLC scan involves updating the status of inputs, executing
the user program, performing diagnostic and communication
functions, and updating the status of outputs. A PLC scan is
repetitively executed.
Plug-in Busway
Busway that incorporates plug-in units, called bus plugs, to
allow loads to be distributed over the length of the run.
Power
The rate at which work is done or energy is transformed. In
an electric circuit, power is measured in watts, or sometimes
in horsepower. The term power is also often used to refer to
electrical energy and as an adjective to describe devices or
circuits designed to carry a high level of current.
Power Factor
The ratio of true power to apparent power in a circuit. Power
factor is also equal to the cosine of the phase angle.
A complete execution cycle of a programmable logic controller.
The PLC scan involves updating the status of inputs, executing
the user program, performing diagnostic and communication
functions, and updating the status of outputs. A PLC scan is
repetitively executed.
Plug-in Busway
Busway that incorporates plug-in units, called bus plugs, to
allow loads to be distributed over the length of the run.
Power
The rate at which work is done or energy is transformed. In
an electric circuit, power is measured in watts, or sometimes
in horsepower. The term power is also often used to refer to
electrical energy and as an adjective to describe devices or
circuits designed to carry a high level of current.
Power Factor
The ratio of true power to apparent power in a circuit. Power
factor is also equal to the cosine of the phase angle.
Letter P
Pad-Mounted Transformer
An enclosed transformer mounted on a concrete pad.
Panelboard
A front-accessible panel containing overcurrent protection
devices for use in controlling lighting and appliance or power
circuits.
Photoelectric Proximity Switch A type of sensing switch that uses light to detect the presence of an object without coming into physical contact with the
object.
Pilot Light
An indicator light typically used to represent a condition in a
machine or process.
Letter Ov
Overcurrent A current in excess of the rated current for a device or
conductor. An overcurrent can result from an overload, short
circuit, or ground fault.
Overload
Can refer to an operating condition in excess of the full-load
rating or a current high enough to cause damage if it is present
long enough. Short circuits and ground faults are not overloads.
Overload Relay
A device used to protect a motor from damage resulting from
an overload.
Overload Relay Class
Defines the length of time an overload condition can exist
before an overload relay trips. For example, a class 10 overload
relay allows 600% of full load amperes for up to 10 seconds.
Letter O
Ohm The basic unit of resistance, reactance and impedance. The
symbol for the ohm is “W”, the Greek letter omega.
Ohmmeter A meter designed to measure resistance.
Ohm’s Law
A law that states that the current in a circuit is directly
proportional to the voltage and inversely proportional to the
resistance.
Open Drip Proof (ODP)
A motor enclosure type that permits air flow through the motor,
but is designed to prevent liquids or solids falling from above
at angles up to 15 degrees from the vertical from entering the
motor.
Open-Loop Control A control technique that does not use a feedback signal.
Letter Ne
NEMA Motor Design
A letter designation based upon standards established by the
National Electrical Manufacturers Association that corresponds
to a motor’s speed and torque characteristics.
Neutral A reference connection in a power distribution system.
A letter designation based upon standards established by the
National Electrical Manufacturers Association that corresponds
to a motor’s speed and torque characteristics.
Neutral A reference connection in a power distribution system.
Letter N
National Electrical Code (NEC ®)® A document revised every three years based upon inputs to and recommendations of volunteer committee members of the
National Fire Protection Association. The intent of the NEC ®,
also called NFPA 70®, is to describe safe electrical practices.
Although the NEC® is an advisory document, its use is often
mandated by state and local building codes.
NEMA Enclosure Type
A designation given to an enclosure based on standards
published by the National Electrical Manufacturers Association.
The NEMA type identifies of the degree of protection provided
by the enclosure.
NEMA Frame Size
A designation that identifies motor dimensions based upon
standards provided by the National Electrical Manufacturers
Association. Motors too large to correspond to NEMA frame
sizes are referred to as above NEMA motors.
National Fire Protection Association. The intent of the NEC ®,
also called NFPA 70®, is to describe safe electrical practices.
Although the NEC® is an advisory document, its use is often
mandated by state and local building codes.
NEMA Enclosure Type
A designation given to an enclosure based on standards
published by the National Electrical Manufacturers Association.
The NEMA type identifies of the degree of protection provided
by the enclosure.
NEMA Frame Size
A designation that identifies motor dimensions based upon
standards provided by the National Electrical Manufacturers
Association. Motors too large to correspond to NEMA frame
sizes are referred to as above NEMA motors.
Letter Mr
Motor Control Center
A metal structure containing multiple motor control units.
Typically, individual control circuits are mounted in removable
containers, often referred to as pans or buckets.
Motor Insulation Class
Standards established by the National Electrical Manufacturers
Association (NEMA) to meet motor temperature requirements
found in different operating environments. The combination of
an ambient temperature of 40°C and allowed temperature rise
equals the maximum winding temperature of a motor. A margin
is also allowed to provide for a point at the center of the motor’s
windings where the temperature is higher.
Motor Starter
Often refers to a contactor and an overload relay assembled
together to remotely control the operation of a motor while
providing overload protection. This definition applies to a
full voltage starter. A variety of other starter types are also
available.
Mutual Induction
A process that occurs when varying lines of magnetic flux from
one conductor induce a voltage in an adjacent conductor. This is
the basic operating principle of a transformer.
A metal structure containing multiple motor control units.
Typically, individual control circuits are mounted in removable
containers, often referred to as pans or buckets.
Motor Insulation Class
Standards established by the National Electrical Manufacturers
Association (NEMA) to meet motor temperature requirements
found in different operating environments. The combination of
an ambient temperature of 40°C and allowed temperature rise
equals the maximum winding temperature of a motor. A margin
is also allowed to provide for a point at the center of the motor’s
windings where the temperature is higher.
Motor Starter
Often refers to a contactor and an overload relay assembled
together to remotely control the operation of a motor while
providing overload protection. This definition applies to a
full voltage starter. A variety of other starter types are also
available.
Mutual Induction
A process that occurs when varying lines of magnetic flux from
one conductor induce a voltage in an adjacent conductor. This is
the basic operating principle of a transformer.
Letter Mo
Molded Case Circuit Breaker
A circuit breaker enclosed in an insulated housing. In the United
States, molded case circuit breakers conform to NEMA AB-1
and UL 489 specifications.
Molded Case Switch
A switch enclosed in the same type of insulated housing as a
molded case circuit breaker. Siemens molded case switches
employ the same operating mechanism as thermal-magnetic
and magnetic only circuit breakers. A preset instantaneous
function is factory installed to allow the switch to trip and
protect itself at a high fault current, but the switch provides no
thermal overload protection or short circuit protection.
Motor (Electric)
A device that transforms electrical energy into mechanical
energy.
..
A circuit breaker enclosed in an insulated housing. In the United
States, molded case circuit breakers conform to NEMA AB-1
and UL 489 specifications.
Molded Case Switch
A switch enclosed in the same type of insulated housing as a
molded case circuit breaker. Siemens molded case switches
employ the same operating mechanism as thermal-magnetic
and magnetic only circuit breakers. A preset instantaneous
function is factory installed to allow the switch to trip and
protect itself at a high fault current, but the switch provides no
thermal overload protection or short circuit protection.
Motor (Electric)
A device that transforms electrical energy into mechanical
energy.
..
Letter M
Main Breaker
The circuit breaker in or upstream from a load center,
panelboard, switchboard, switchgear or other equipment that
supplies the full current for that equipment.
Main Lug
Only A designation given to indicate that a main breaker or main
switch is not included.
MCM
Abbreviation for a thousand circular mils. Circular mills are used
to designate the cross-sectional area of a round conductor.
One mill is equal to 1/1000 of an inch. The circular mill area of a
solid, round conductor is calculated by squaring the conductor’s
diameter (in mills). 1 MCM is 1000 circular mils (also shown as
1 kcmil).
Metric Unit Prefix
A prefix added to a unit of measure to increase or decrease the
size of that unit of measure. For example, the metric unit prefix
kilo can be added to meter to form a unit of length (kilometer)
equal to 1000 meters. Metric unit prefixes are associated with
powers of ten.
The circuit breaker in or upstream from a load center,
panelboard, switchboard, switchgear or other equipment that
supplies the full current for that equipment.
Main Lug
Only A designation given to indicate that a main breaker or main
switch is not included.
MCM
Abbreviation for a thousand circular mils. Circular mills are used
to designate the cross-sectional area of a round conductor.
One mill is equal to 1/1000 of an inch. The circular mill area of a
solid, round conductor is calculated by squaring the conductor’s
diameter (in mills). 1 MCM is 1000 circular mils (also shown as
1 kcmil).
Metric Unit Prefix
A prefix added to a unit of measure to increase or decrease the
size of that unit of measure. For example, the metric unit prefix
kilo can be added to meter to form a unit of length (kilometer)
equal to 1000 meters. Metric unit prefixes are associated with
powers of ten.
Letter L
Ladder Logic
A method of programming a programmable logic controller that
uses symbols that evolved from the diagrams used with control
relays.
Limit Switch
A type of switch that opens or closes its contacts when its
actuator is moved by an object.
Load Center
An industry term used to identify a lighting and appliance
panelboard designed for use in residential and light commercial
applications.
Local Area Network (LAN)
A communication system that interconnects devices within a
limited area, but may also connect to other networks for largerscale
communication.
Letter J,K
Joule
The basic unit of electrical energy. 1 Joule is equal to 1 wattsecond
or the amount of energy transferred in one second
when the power is one watt.
Knockout
A place in an enclosure where a piece of the enclosure can be
easily removed to allow for cable entry.
Letter Iv
Insulator
A material with a high resistance to the flow of electrons.
Plastic, rubber, glass, and mica are examples of materials that
are good insulators.
Interrupting Rating
The maximum level of fault current that a circuit breaker or fuse
can safely interrupt at a specific voltage. The interrupting rating
is also called the ampere interrupting rating.
Inverter
A device that converts direct current to alternating current.
Inverter is also used as a synonym for an AC drive even though
the AC drive usually includes other circuits.
Isolation Transformer A transformer used to limit the transfer of electrical noise from
one circuit to another.
Letter In
Instrument Transformer
A type of transformer used to sense the voltage or current
of associated conductors and provide proportional electrical
energy to measurement devices or circuits. A potential
transformer (PT) is used for voltage measurements and a
current transformer (CT) is used for current measurements.
Insulated Case Circuit Breaker A type of circuit breaker that conforms to NEMA AB-1 and
UL 489 standards for molded case circuit breakers and is often
used as a main breaker in switchboards, motor control centers,
or in other applications requiring a molded case circuit breaker
with a high continuous current rating.
Insulated Gate Bipolar Transistor (IGBT) A type of transistor often used as a switching device in the inverter section of a variable frequency drive. Voltage on the gate element is used to control the current flowing between the collector and emitter.
A type of transformer used to sense the voltage or current
of associated conductors and provide proportional electrical
energy to measurement devices or circuits. A potential
transformer (PT) is used for voltage measurements and a
current transformer (CT) is used for current measurements.
Insulated Case Circuit Breaker A type of circuit breaker that conforms to NEMA AB-1 and
UL 489 standards for molded case circuit breakers and is often
used as a main breaker in switchboards, motor control centers,
or in other applications requiring a molded case circuit breaker
with a high continuous current rating.
Insulated Gate Bipolar Transistor (IGBT) A type of transistor often used as a switching device in the inverter section of a variable frequency drive. Voltage on the gate element is used to control the current flowing between the collector and emitter.
Letter Iu
Inductive Reactance
The opposition to alternating current resulting from circuit
inductance. Inductive reactance is directly proportional to
frequency (f) and inductance (l). The symbol for inductive
reactance is “XL” The unit for inductive reactance is the ohm.
Inductor
A device manufactured to have a specific inductance. An
inductor is often made from a coil of wire and is sometimes
called a coil or choke.
Input/Output (I/O) System
The part of a control system that interfaces to the real world.
The I/O system accepts signals from switches and sensors, and
provides signals to actuating and display devices.
Letter I
IEEE
An organization open to individual membership that provides a
variety of services for its members, but also develops numerous
standards for technology and practices. The organization is
now officially known as IEEE (pronounced eye-triple-e) and no
longer refers to itself as the Institute of Electrical and Electronic
Engineers.
Impedance
The total opposition to alternating current. Impedance is
the vector sum of resistance and reactance. The symbol for
impedance is “Z.” The unit for impedance is the ohm.
Inductance
The property of an electrical circuit that opposes changes in
current. Inductance is designated by the symbol “L” and is
measured in henries.
Inductive Proximity Switch
A type of sensing switch that uses an electromagnetic coil
to detect the presence of a metal object without coming into
physical contact with it.
An organization open to individual membership that provides a
variety of services for its members, but also develops numerous
standards for technology and practices. The organization is
now officially known as IEEE (pronounced eye-triple-e) and no
longer refers to itself as the Institute of Electrical and Electronic
Engineers.
Impedance
The total opposition to alternating current. Impedance is
the vector sum of resistance and reactance. The symbol for
impedance is “Z.” The unit for impedance is the ohm.
Inductance
The property of an electrical circuit that opposes changes in
current. Inductance is designated by the symbol “L” and is
measured in henries.
Inductive Proximity Switch
A type of sensing switch that uses an electromagnetic coil
to detect the presence of a metal object without coming into
physical contact with it.
Letter Hx
Hexadecimal
A number system that uses powers of 16 .
Horsepower
A unit of power. Horsepower is abbreviated “HP.” 1 horsepower
is equal to 746 watts.
Letter H
Harmonics
The base frequency produced by a circuit is said to be the
fundamental frequency or first harmonic. Additional harmonics
are multiples of the first harmonic. The 3rd harmonic of a 60 Hz
power supply, for example, is 3 x 60 Hz = 180 Hz.
Harmonic Distortion
The effect of harmonics on the fundamental frequency.
Harmonic distortion can interfere with the operation of
electronic devices.
Henry
The basic unit of inductance. The symbol for the henry is “H.”
Hertz
A unit of frequency equal to one cycle per second. Hertz is
abbreviated Hz.
The base frequency produced by a circuit is said to be the
fundamental frequency or first harmonic. Additional harmonics
are multiples of the first harmonic. The 3rd harmonic of a 60 Hz
power supply, for example, is 3 x 60 Hz = 180 Hz.
Harmonic Distortion
The effect of harmonics on the fundamental frequency.
Harmonic distortion can interfere with the operation of
electronic devices.
Henry
The basic unit of inductance. The symbol for the henry is “H.”
Hertz
A unit of frequency equal to one cycle per second. Hertz is
abbreviated Hz.
Letter G
Ground A connection to the earth or to a conductive object such as an equipment chassis.
Ground Fault
A condition in which current takes an unintentional path to
ground. Ground faults can endanger people and damage
equipment. For this reason, some circuits are equipped with a
ground fault circuit interrupter (GFCI).
Ground Fault Circuit Interrupter (GFCI) A device designed to interrupt current in a circuit if a ground fault is sensed. If a GFCI is installed near the receptacles it
protects, overcurrent protection is required separately. A GFCI
circuit breaker combines protection for ground faults, overloads,
and short circuits in one device.
Ground Fault
A condition in which current takes an unintentional path to
ground. Ground faults can endanger people and damage
equipment. For this reason, some circuits are equipped with a
ground fault circuit interrupter (GFCI).
Ground Fault Circuit Interrupter (GFCI) A device designed to interrupt current in a circuit if a ground fault is sensed. If a GFCI is installed near the receptacles it
protects, overcurrent protection is required separately. A GFCI
circuit breaker combines protection for ground faults, overloads,
and short circuits in one device.
Letter Fu
Fuse
A device designed to open a circuit when its rated current is
exceeded. This is usually accomplished when a metal link in the
fuse melts. Renewable fuses allow the user to replace the link
and non-renewable fuses do not. Fuses are available in various
sizes and types. Some have a time delay.
Fuse Class
A letter designation given to a fuse to identify its operating and
construction characteristics.
Letter Fi
Filler Plates
Plates used to cover unused spaces in a panel.
Four-Quadrant Operation
Describes the operation of a variable speed drive that is capable
of providing forward or reverse torque with the motor rotating in
either the forward or reverse direction.
Frequency
The rate of variation of a periodic waveform. The symbol for
frequency is “f.” The unit for frequency is Hertz.
Full-Voltage Starter
A type of motor starter often used for three-phase induction
motors that applies the full line voltage to the motor
immediately. Sometimes called an across-the-line starter.
Letter F
Farad
The basic unit of capacitance. The symbol for the farad is “F.”
Feedback
A signal provided to a control circuit that is representative of an
actual condition in a machine or process.
Feeder
Often refers to a set of conductors that originates at a main
distribution center and supplies power to one or more
secondary or branch distribution centers.
Feeder Busway
Busway used to distribute feeder current to loads that are
sometimes remote from the power source.
The basic unit of capacitance. The symbol for the farad is “F.”
Feedback
A signal provided to a control circuit that is representative of an
actual condition in a machine or process.
Feeder
Often refers to a set of conductors that originates at a main
distribution center and supplies power to one or more
secondary or branch distribution centers.
Feeder Busway
Busway used to distribute feeder current to loads that are
sometimes remote from the power source.
Letter EX
Explosion Proof (XP)
A motor enclosure type used in hazardous locations. Explosion
proof enclosures are also available for other types of equipment.
A motor enclosure type used in hazardous locations. Explosion
proof enclosures are also available for other types of equipment.
Letter E
Effective Value
A measure of the amplitude of alternating current or voltage.
Also called the root-mean-square or RMS value. Test meters
used to measure alternating current or voltage usually display
effective values.
EEPROM A type of semiconductor memory often used for storage of
data or programs that change less frequently than rand access memory. The contents of EEPROM chips are erased with electrical pulses rather than with ultraviolet light as with erasable programmable read only memory. EEPROMs retain
their contents when power is turned off.
Enclosure
A protective housing. Guidelines for various types of
electrical enclosures are provided by the National Electrical
Manufacturers Association (NEMA). and International
Electrotechnical Commission (IEC).
Encoder
Often refers to a digital device that provides angular position
information. Some encoders provide this information as
incremental pulses as position changes. Other types of
encoders provide a digital signal representative of absolute
position.
..
A measure of the amplitude of alternating current or voltage.
Also called the root-mean-square or RMS value. Test meters
used to measure alternating current or voltage usually display
effective values.
EEPROM A type of semiconductor memory often used for storage of
data or programs that change less frequently than rand access memory. The contents of EEPROM chips are erased with electrical pulses rather than with ultraviolet light as with erasable programmable read only memory. EEPROMs retain
their contents when power is turned off.
Enclosure
A protective housing. Guidelines for various types of
electrical enclosures are provided by the National Electrical
Manufacturers Association (NEMA). and International
Electrotechnical Commission (IEC).
Encoder
Often refers to a digital device that provides angular position
information. Some encoders provide this information as
incremental pulses as position changes. Other types of
encoders provide a digital signal representative of absolute
position.
..
Letter Di
Discrete I/O
Inputs (I) and outputs (O) that are either on or off.
Distribution Section
A switchgear, switchboard , or power panelboard section that
receives power from the service section and distributes power
to other circuits.
Duty Cycle
The ratio of a device’s on time to its total cycle time. Duty cycle
is normally expressed as a percentage; therefore, a device with
a 50% duty cycle is on half the time.
Letter De
Digital
Used to describe circuits that use on or off (binary) signals. Also
used to describe equipment that includes these circuits.
DIN Rail
A mounting bracket manufactured to German Institute for
Standardization (DIN) standards. Typically used to mount
devices such as small PLCs, motor starters, control relays,
power supplies, and other components that are DIN rail
compatible.
Diode
A component with two terminals (anode and cathode) that
passes current primarily in one direction. Often used as part of
a rectifier circuit.
Direct Current (DC) Current with a constant direction.
Disconnect Switch
A switch designed to disconnect electrical power from a circuit.
Letter D
DC Drive
An electronic device used to control the speed of a DC motor.
The term variable speed drive applies to both DC Drives and AC
Drives.
DC Motor
A motor that converts direct current electrical energy into
mechanical energy.
Dead Front
A front portion of a panelboard or switchboard that limits
exposure to electrical connections.
Delta
A connection arrangement used for the primary and/or
secondary of a three-phase transformer.
..
An electronic device used to control the speed of a DC motor.
The term variable speed drive applies to both DC Drives and AC
Drives.
DC Motor
A motor that converts direct current electrical energy into
mechanical energy.
Dead Front
A front portion of a panelboard or switchboard that limits
exposure to electrical connections.
Delta
A connection arrangement used for the primary and/or
secondary of a three-phase transformer.
..
Letter Co
Counter EMF
A voltage created in an inductive circuit that opposes a change
in current flow. EMF stands for electromotive force.
Crest Factor
The ratio of the peak value of an alternating current to its
effective value.
Current
The flow of electrons in a circuit. Current is designated by the
symbol “I” and is measured in amperes.
letter Cy
Contactor
Usually refers to a device with large contacts that close when
current is applied to its electromagnet; however, solid state
contactors are also available. Contactors are used to control the
power applied to motors, lights, or heating components.
Control Relay
Usually refers to a device with contacts that open and close
electromagnetically, but solid state control relays are also
available. Control relays typically handle smaller currents than
contactors, but are capable of switching more rapidly.
Coulomb
A unit of electrical charge moved in 1 second by a current of 1
ampere. This is equal to approximately 6.24 x 1018 electrons.
Coulomb’s Law
A law that states that charged objects attract or repel each
other with a force that is directly proportional to the product
of their charges and inversely proportional to the square of the
distance between them.
letter Cp
Central Processor Unit (CPU) The decision-making part of a computer. May also be used to describe the processing circuits together with memory and other circuits needed for processing information.
Circuit Breaker A device that can be used to open or close a circuit manually and also opens a circuit automatically when it senses an overcurrent.
Closed-Loop Control A control technique that compares a feedback signal representative of an actual value with a desired value and
responds to minimize the error.
Conductor
A material that permits electrons to easily move through it.
Copper, silver, and aluminum are examples of materials that are
good conductors. Also used generically to refer to a wire, cable,
or bus bar that is made from a conducting material.
Circuit Breaker A device that can be used to open or close a circuit manually and also opens a circuit automatically when it senses an overcurrent.
Closed-Loop Control A control technique that compares a feedback signal representative of an actual value with a desired value and
responds to minimize the error.
Conductor
A material that permits electrons to easily move through it.
Copper, silver, and aluminum are examples of materials that are
good conductors. Also used generically to refer to a wire, cable,
or bus bar that is made from a conducting material.
letter C
Capacitance The property of a circuit or device that allows it to store an electrical charge. The symbol for capacitance is “C.” The unit for capacitance is the farad.
Capacitive Proximity Switch A type of sensing switch that produces an electrostatic field to detect the presence of an object without touching the object.
Capacitive Reactance The opposition to alternating current resulting from circuit
capacitance. Capacitive reactance is inversely proportional to
frequency (f) and capacitance (C). The symbol for capacitive
reactance is “XC.” The unit for capacitive reactance is the ohm.
Capacitor A device manufactured to have a specific capacitance.
Capacitive Proximity Switch A type of sensing switch that produces an electrostatic field to detect the presence of an object without touching the object.
Capacitive Reactance The opposition to alternating current resulting from circuit
capacitance. Capacitive reactance is inversely proportional to
frequency (f) and capacitance (C). The symbol for capacitive
reactance is “XC.” The unit for capacitive reactance is the ohm.
Capacitor A device manufactured to have a specific capacitance.
letter Br
Bus A group of conductors used to supply power, data, or control signals.
Bus Bar A conductor that serves as a common connection for two or more circuits.
Bus Plug A device used with plug-in busway to provide power connections close to the intended load.
Busway A prefabricated electrical distribution system that uses bus bars in a protective enclosure.
Busway Hangers Devices used to suspend busway from a ceiling or mount it to a
wall.
Byte Eight consecutive bits.
Bus Bar A conductor that serves as a common connection for two or more circuits.
Bus Plug A device used with plug-in busway to provide power connections close to the intended load.
Busway A prefabricated electrical distribution system that uses bus bars in a protective enclosure.
Busway Hangers Devices used to suspend busway from a ceiling or mount it to a
wall.
Byte Eight consecutive bits.
letter B
Binary-Coded Decimal Usually refers to the 8-4-2-1 code where four bits are used to
(BCD) represent decimal digits 0 through 9.
Binary Number A number made up only of 1’s and 0’s that represent powers
of two (2). Digital equipment uses binary numbers to represent
numerical values and the on or off condition of devices.
Bit A 1 or 0 representing one position in a binary number.
Bonding The permanent joining of metal parts to form an electrically conductive path.
Branch Circuit A part of a power distribution system extending beyond the
final overcurrent protection device.
(BCD) represent decimal digits 0 through 9.
Binary Number A number made up only of 1’s and 0’s that represent powers
of two (2). Digital equipment uses binary numbers to represent
numerical values and the on or off condition of devices.
Bit A 1 or 0 representing one position in a binary number.
Bonding The permanent joining of metal parts to form an electrically conductive path.
Branch Circuit A part of a power distribution system extending beyond the
final overcurrent protection device.
letter ar
Arc Fault An electrical arc which causes current to flow in unintended
ways, but often not in sufficient amounts to cause a standard
circuit breaker to trip. Arc faults result from worn or damaged
insulation and are a common cause of fires.
Arc Fault CircuitInterrupter (AFCI)A circuit breaker designed to provide protection from the effects of an arc fault by recognizing the characteristicsunique to arcing and de-energizing the circuit when an arc
fault is detected. The most effective AFCI circuit breakers are
combination AFCIs which provide protection against all three
known types of arc faults.
Autotransformer A type of transformer in which the secondary coil is part of the
primary coil. Often the secondary voltage is adjustable via a
movable tap.
ways, but often not in sufficient amounts to cause a standard
circuit breaker to trip. Arc faults result from worn or damaged
insulation and are a common cause of fires.
Arc Fault CircuitInterrupter (AFCI)A circuit breaker designed to provide protection from the effects of an arc fault by recognizing the characteristicsunique to arcing and de-energizing the circuit when an arc
fault is detected. The most effective AFCI circuit breakers are
combination AFCIs which provide protection against all three
known types of arc faults.
Autotransformer A type of transformer in which the secondary coil is part of the
primary coil. Often the secondary voltage is adjustable via a
movable tap.
letter am
Ammeter A meter designed to measure current.
Ampacity The continuous current rating in amperes for a conductor.
Ampere, Amp The basic unit for current. An ampere, also called an amp, is
equal to a current of 1 Coulomb per second. The symbol for
ampere is “A.”
Amplitude The total variation of a waveform. Amplitude can be expressed
as a peak value, peak-to-peak value, or effective value.
Analog A value that is continuously variable. Also used to describe
Analog Input An input to a system that can continuously vary over a range of
current or voltage such as 4 to 20 milliamps or 0 to 10 volts.
circuits that work with analog signals.
Analog Output An output from a system that can continuously vary over a
range of current or voltage such as 4 to 20 milliamps or 0 to 10
volts.
Apparent Power The vector sum of true power and reactive power. Apparent
power is calculated by multiplying current times voltage. The
unit for apparent power is the volt-ampere, abbreviated “VA.”
Arc Chute Assembly An assembly of metal plates surrounding circuit breaker or
contactor contacts. Arc chutes are used to reduce contact
damage by quickly extinguishing the arc created when contacts
open.
Ampacity The continuous current rating in amperes for a conductor.
Ampere, Amp The basic unit for current. An ampere, also called an amp, is
equal to a current of 1 Coulomb per second. The symbol for
ampere is “A.”
Amplitude The total variation of a waveform. Amplitude can be expressed
as a peak value, peak-to-peak value, or effective value.
Analog A value that is continuously variable. Also used to describe
Analog Input An input to a system that can continuously vary over a range of
current or voltage such as 4 to 20 milliamps or 0 to 10 volts.
circuits that work with analog signals.
Analog Output An output from a system that can continuously vary over a
range of current or voltage such as 4 to 20 milliamps or 0 to 10
volts.
Apparent Power The vector sum of true power and reactive power. Apparent
power is calculated by multiplying current times voltage. The
unit for apparent power is the volt-ampere, abbreviated “VA.”
Arc Chute Assembly An assembly of metal plates surrounding circuit breaker or
contactor contacts. Arc chutes are used to reduce contact
damage by quickly extinguishing the arc created when contacts
open.
letter a
AC Drive An electronic device used to control the speed of an AC motor.
Also called a variable frequency drive and an inverter. The term
variable speed drive applies to both AC Drives and DC Drives.
AC Motor A motor that uses alternating current to convert electrical
energy into mechanical energy. Many AC motors used in
industrial applications are three-phase induction motors.
Alternating Current (AC) Current that periodically reverses direction.
Ambient Temperature The temperature of the medium (air, water, etc.) surrounding a
device.
Also called a variable frequency drive and an inverter. The term
variable speed drive applies to both AC Drives and DC Drives.
AC Motor A motor that uses alternating current to convert electrical
energy into mechanical energy. Many AC motors used in
industrial applications are three-phase induction motors.
Alternating Current (AC) Current that periodically reverses direction.
Ambient Temperature The temperature of the medium (air, water, etc.) surrounding a
device.
Subscribe to:
Posts (Atom)
Posts
