Rules, Definitions, Acronyms, & Formulas Flashcards
Voltage remains the same in a _____.
Parallel circuits ____ remains the same.
Current remains the same in _____ ckt.
Series ckt ____ remains the same.
Formula to find resistance in a series ckt :
Rt = R1 + R2 + R3 + R4…
To find resistance in a parallel ckt
Reciprocal
Product over sun
A method used to find resistance when you have two values in a parallel ckt
How do you find inductance in a parallel ckt?
Use the same as reciprocal
Formula for capacitive reactance
XC = 1/2(3.14)(f)(c)
Formula for inductive reactance
XL = 2(3.14)(f)(l)
Stationary part of a motor is called a ___.
Stator is the _____ part of an AC motor.
Rotating member of an AC motor is called ___.
Rotor is the ____ part of an AC motor.
The stationary part of an D.C. motor is a ____.
Field frame is the ___ of D.C. Motor.
Three types of DC motors:
Shunt
Series
Compound
Formula for synchronous speed
RPM = 120 x F
Formula for the actual speed of a motor:
Synchronous speed - slip
The average of all the instantaneous AC values during 1/2 cycle. The average value of a complete cycle is 0
AC Average
The AC level of power that will produce the same amount of heat produced by an equivalent DC power. Also referred to as the RMS (root means square) value
AC effective
The speed of the rotating field (sychronous) determined by the frequency and the number of poles
AC RPM
speed of the rotor in an AC motor determined by the load. Close to synchronous speed at no load and matches the nameplate at full load
Actual Speed
ease at which AC current flows in a circuit
Admittance
Maximum value that the current at full field and full armature voltage for a particular design
Amplitude
The speed of the armature at full at full speed and full armature voltage for a particular design.
base speed
the movement of electrons in a circuit as they are influenced by a magnetic field.
basic induction
max torque an AC motor developed under load without an abrupt drop in speed. the rotor will have a 45 degree phase angle
breakdown torque
the ability to store energy in an electrostatic field
capacitance
ability of a component to conduct
conductance
the speed of an armature determined by the design of the motor itself. Max is at full armature and full field
DC RPM
A potential or energy per unit of charge measured in volts
electromotive force
the direction of electrons as they flow from valence ring to valence ring, from negative to positive
electron flow
the weakening of the stationary field in a DC motor which will allow an increase in armature speed with loss of torque
field weakening
The force field of a magnet with the strongest point at the poles. the field surrounding a conductor with current flowing on it.
Flux
Number of magnetic flux lines per cross sectional area.
flux density
total opposition to current flow in an AC circuit, combining the counter voltage (XL) and the resistance (R)
impedance
The ability to store energy in an electromagnetic field.
inductance
the force that is produced by the by the magnetic lines in a circuit
magnamotive force
the ability of a material to keep the magnetic domains aligned and maintain the residual magnetic force.
permeance
the process of inducing current and voltage in a conductor as a direct result of current flow in another
mutual induction
the ability of a material to allow the passage of magnetic lines of flux as compaired to air.
permeability
a difference in charges between two points. A negative potential has an excess of electrons and a positive potential has an absence of electrons
potential
the amount of work that can by a load in a standard amount of time, usually one second. Can be useful (wall heater) or wasted (bad connection)
power
the ratio of true power (KW) to apparent power (KVA). AC motors with an uncorrected ___ run at 80%
power factor
the opposition to current flow in a DC ckt
resistance
opposition to current low in an AC ckt & the opposition to change. it is counter voltage that is induced in the ckt and can be inductive or capacitive
reactance
the opposition to magnetic lines of flux or a magnetic field
reluctance
an AC ckt where the XL and the XC have cancelled each other by being equal and the reactance is zero
resonance
AC: the interaction between the rotating field in the stator and the induced field in the rotor.
DC: the interaction between the stationary field (shunt, series, both) and the field in the armature.
rotation
the frequency induced in the rotor determined by the rotating field in the stator.
rotor frequency
inducing a counter voltage to the source determined by the direction of the flux as the source current flows in a ckt
self induction
a multiplier used on a nameplate that allows a motor to run over the rated current and horsepower for short periods
service factor
the difference in the speed of the rotor and rotating field in the stator
slip
the speed of the rotating field in a polyphase stator determined by the source frequency and the number of poles
synchronous speed
a turning or twisting force measured in foot pounds
torque
ELI the ICE man (inductive circuits - L)
voltage (E) leads the current (I)
ELI the ICE man * capacitive ckt’s - C)
current (I) leads the voltage (E)
the relationship and the effect of current, voltage, and resistance in a ckt. 1 volt applied to 1 ohm allows 1 amp of current flow
ohms law
induced current in any ckt creates a field that is always in such a direction as to oppose the field that caused it (CEMF)
Lenz’s Law
the sum of the voltage drops around any closed loop in a ckt is equal to the sum of EMF’s in that loop
Kirchhoff’s law = voltage
the sum of the current arriving at any junction point in a ckt is equal to the sum of the current leaving that point
Kirchhoff’s law = current
I (squared) R losses due to the resistnace of the winding dissipated in heat and temperature coefficient.
Copper loss (heat loss)
power consumed in an AC ckt to align molecules (magnetic domains) in a magnetic material each time the polarity changes.
hysteresis
lines of flux that miss the core and leak into space
flux leakage
circulating currents in the core that consume power. laminating the core will reduce the cross sectional area and reduce the current in the material
eddy currents
the point at which the core cannot hold any more magnetic lines of flux due to any increase in current
saturation
A rotor has ___, while an armature has a ____
(Slip rings) are found in a ___, while a (commutator) is part of a ___.
A rotor produces its poles through ___, while an armature produces its poles through a connected ____.
(Induction) creates poles in a ____ of a motor, while a (connected power supply) produces the poles in a an _____.
A ckt that is 10 times more resistive than it is inductive is considered ____, whereas a ckt that is 10 times more inductive than it is resistive is considered ____.
purely resistive
purely inductive
A magnetic field will surround a conductor as a direct result of ___ in that conductor & is proportional to the amount of ___.
current
the four factors that determine capacitance can be found by using the acronym D.A.N.S.
D = dielectric matter A= area of the plates N= number of the plates S= spacing of the plates
these four factors determine ____.
The four factors that determine inductance of an inductor by using the word CoNTroL
C = cross section of core
N= number of turns
T= type of core
L=length of the coil
these four factors determine ____.
measurement of current
amp
measurement of capacitance
Farad
measurement of inductance
Henry
measurement of conductance
MHO
measurement of resistance
ohm
measurement of potential
volt
measurement of power
watt
“C” = ___
symbol for capacitance
“E” = ____
symbol for voltage
“G” =
symbol for conductance
“FLA” =
symbol for full load amps
“H”
symbol for Henry
“I” =
symbol for current
“LRA” =
symbol for locked rotor amps
“P” =
symbol for power
“R” =
symbol for resistance
“SF” =
symbol for service factor
“X” =
symbol for reactance
“Z” =
symbol for impedance
“CEMF” =
symbol for counter electro motive force
“EMF” =
symbol for electro motive force
“MMF” =
symbol for magna motive force
I x E , I(sq) x R , E(sq) / R
formulas for power (P)
I x R , P/I , sq root of (P x R)
formulas for volts (E)
P/E , E/R , sq root of (P/R)
formulas for amps (I)
E/I , E(sq)/P , P/I(sq)
formuals for ohms (R)
Current in amperes is ____ to the voltage in volts and ____ to resistance in ohms
directly proportional
inversely proportional
when current finds an alternate path back to the source, rather than taking the path through the load, it is called a ____.
short circuit
current is _____ proportional to resistance in a ckt.
(“inversely” proportional:) the relationship btwn ____ and ____ in a ckt.
When the negative terminal of one battery is connected to the positive terminal of the next battery in a series ckt, it causes the ____ to be added to the next.
(voltage) is added when the negative terminal of one battery is added to the positive terminal of the next in a ____ type of ckt.
If power sources are connected so that their polarities are not in the same directions, they will oppose each other
E(total) = E(larger) - E(smaller)
the total ___ in a ckt always equals the source voltage.
total (voltage drop) in a is always equal to the ____.
If a ckt is ___, no current will flow.
if a ckt is (open) no _____ will flow.
___ is constant in a series DC ckt.
current is constant in ____ DC ckt
the current through any resistor is series with source voltage is equal to the total ____.
Total (current) is equal to source voltage when current flows through any resistor in ____ type of ckt.
The ___ across a resistor is equal to I x R regardless of the type of circuit.
“voltage drop” is equal to ____ (formula) regardless of the type of ckt
____ delivered to circuit is the measure of the amount of work done by a circuit per unit of time
power
as the current through a series circuit decreases, the total power dissipated in each component decreases.
relationship between current and power in a series ckt
The purpose of ____ in an electrical ckt is to cause electrons to flow.
voltage
An open in any branch of a parallel ckt will cause a decrease in total ____.
current
for a ckt to be considered a parallel ckt, there must be at least ____ of current flow
two paths
the unit of measurement of electrical power is the ____
watt
___ is a special type of adjustable resistor that is used to adjust the current in a branch of a ckt
rheostat
Three way switches are also known as ____
single pole, double throw switches SPDT
three way and four way switches shall be so installed that all switching is done in the ______
ungrounded ckt conductors
Fuses and ckt breakers are primarily designed to protect ____, ____, ____.
conductors, components, and equipment are protected by fuses and ckt breakers.
overcurrent devices such as ckt breakers and fuses are connected in ____ with the load.
series
Find the circular mils of a wire
diameter squared
____ is generated anytime current flows through a wire.
heat
a condition of no resistance and very high current is called a _____
short ckt
A ___ is an unintentional connection between an ungrounded conductor and any grounded raceway, box, enclosure, or fitting
ground fault
A GFCI will not protect a person from ____ contact hazards.
line to line
A GFCI will protect a person from _____ and ___ contact hazards.
line to neutral
line to ground
A GFCI (ground fault circuit interrupter is a device intended for the protection of personnel that functions to de-energize a ckt or portion thereof within an established period of time when a current to ___ exceeds ___ ma.
ground / ma
A(n) ____ is the operation of equipment in excess of normal, full-load rating or of a conductor in excess of rated ampacity, that when it persists for a sufficient length of time, would cause damage or dangerous overheating.
overload
____ is the maximum current, in amperes, that a conductor can carry continuously under the conditions of use w/o exceeding its ____ rating.
Ampacity
temperature rating
Conductors of branch ckt’s shall be sized to allow for maximum voltage drop of ___ supplying light, heat, or power & the maximum voltage drop allowable for feeders & branch ckt’s combined shall not exceed ___.
3%
5%
In a three wire, single phase system, the line to line voltage is ____ volts.
240 volts
In a three wire single phase system, the size of the neutral conductor is ____ % of the line conductors.
100%
The single greatest advantage of alternating current is the fact that AC current can be ____ & DC current cannot.
transformed
Copper losses are the I^2 x R in the windings of the _____ and ____.
field and armature
____ are currents induced in metals by changing magnetic fields and can produce enough heat in high current ckts to melt the insulation surrounding the conductors.
eddy currents
____ affects metals made of magnetic materials such as iron and steel caused by molecular friction from rapid magnetization and demagnetization, also producing heat.
Hysteresis.
The voltages of a three phase system are spaced ____ apart.
120 degrees
The maximum amount of voltage attained by the wave form.
peak value
The RMS value of voltage will produce as much power as a like amount of ____.
DC voltage
The total opposition to current flow in an AC circuit is most accurately referred to as the circuit’s ____.
impedance.
Two metal plates separated by a dielectric best describes a ____.
capacitor
A magnetic field is created around a conductor whenever ____.
current flows through a conductor.
The maximum points of the sine wave are at ___ and ___.
90 and 270 degrees
The minimum points of a sine wave are at ___ and ___.
0, 180, and 360 degrees
Skin effect is proportional to ____.
frequency
Skin effect can be reduced by using conductors with ____.
large surface area
In a wye connected system: E-line = ____
E-phase x 1.73
120v x 1.732 = 208v
In a delta connection E-line = ____
E-phase
480v = 480v
The ration of true power to apparent power
power factor
Single phase alternating voltage can be produced by rotating a magnetic field through the conductors of a ____.
stationary coil
Neutral current in a three-wire, single phase system will flow only when there is a(n) ____.
unbalance
An inductor stores energy in the form of a ____.
magnetic field
A three phase power source can be produced by rotating a magnetic field through _____.
3 sets of coils arranged 120 degrees apart.
In an AC ckt, current and voltage are in phase at the ____.
resistors
As an AC ckt adds parallel branches for current to flow, the ckt’s impedance will ____.
decrease
Poor power factor in a plant is normally caused by ____.
inductive loads
An electric device that uses electromagnetism to change voltage from one level to another level or to isolate one voltage from another.
transformer
The power in a single phase ckt drops to zero ___ times in a cycle.
two
Receptacles in dwelling units shall be installed such that no point measured horizontally along a floor line of any wall space is more than ____ from a receptacle outlet.
6 feet
A list of detailed job requirements under which all work must be performed is known as ____.
specifications
Bridge type ____ produce full-wave ____. both the positive and negative half of the AC wave form are changed to DC.
rectifier / rectification
____ ckt breakers are the most common type found in the electrical business.
molded case
In a wye-connected system, the only current that flows in the neutral wire is the ____.
unbalanced current
In a 3-phase ckt, power varies during a cycle, but never ___.
falls to zero
Before the aught sizes start, the largest size building wire listed in wire gauge number is ___.
1 AWG
The primary winding of a transformer is connected to the ____.
power line
The secondary winding is connected to the ____.
load
Dry-type transformers installed indoors and rated 112.5kVA or less shall have a separation of at least ___ from combustible material unless separated from the combustible material by a fire resistive, heat-insulated barrier.
12”
____ have only one winding which is used as both the primary and the secondary.
autotransformers
The NEC requires that a high leg be identified by an ____ or by tagging.
orange wire
Transformers are rated in ____ because the true power is determined by the ___ of the load.
kilo-volt-amps / power factor
Three phase transformer systems require about ____ than single phase systems to deliver the same amount of power to all loads.
25% less copper.
The current carrying capacities for most solid-state relays is less than ____ amperes.
ten
Section ___ of the NEC requires bonding all non current-carrying metal parts of the electrical distribution system together with inter-connenction to the grounded service neutral conductor or other grounded service conductor to from the ground fault path return.
250
Approved grounding electrodes are:
metal underground water pipe, metal frame of the building or structure, concrete encased electrodes, ground ring, and supplemental electrodes.
This must be run to each service disconnecting means, bonded to service disconnecting means enclosure, routed with phase conductors, & must be sized no smaller than the grounding electrode conductor (GEC).
grounded service conductor
In the service equipment panel, this should be used as the common tie point for all other grounding and bonding of the equipment.
grounded neutral busbar
From the point of entry or attachment to the building, to a bus in the service equipment enclosure, this is the common tie point for all ground fault return on both the supply and load sides of the service equipment
grounded service entrance neutral conductor
the grounding electrode establishes an electrical connection to ____.
earth
the maximum number of auxiliary contacts which can normally be installed on a magnetic contactor is ___.
eight
AC ckts of ____ volts or more must be grounded in accordance with NEC section ____.
50 / 250
devices which are activated by a magnetic field produced by an electrical current in a conductor.
electromechanical devices
a discrete switch (on/off) used to control the level in a tank is called a ____.
float switch
NEMA AC motors are designed ___ hertz power.
60
Motor power is rated in ___ or ____.
horsepower / watts
A relay that uses a resistive heating element to open a set of contacts.
thermal overload
a condition that causes the current to rise hundreds of times higher than normal at a very fast rate.
short ckt
an unintentional connection between an ungrounded conductor and any grounded raceway, box, enclosure, or fitting.
ground fault
a three position switch that can be used to manually change the direction of a three phase motor
drum switch
These generally step down the main line voltage to a control voltage of 120 or 24 volts AC.
control transformers
the most common system for industrial control applications
grounded system
a term used to describe a relay which enables the energy in a high powered ckt to be switched by the low powe ckt in a control system
interposing relay
relays that protect the motor of a motor ckt
overload relays
damage may occur to an AC motor if the supply voltage is varied more than ___ above or below the rated nameplate voltage
10%
electrical ratings including voltage rating, current rating, frequency rating, and phase are listed on the ___
motor nameplate
a single phase AC motor that includes a run winding and a resistive start winding used in applications such as fans, business machines, machine tools, and centrifugal pumps where starting is easy.
split-phase motor
the direction of rotation of a 3 phase motor can be reversed by interchanging ___
any two of the 3 phase power lines to the motor
the direction of rotation of a single phase motor can be reversed by switching the ___
two start leads, reversing the current and the poles in the rotor
a motor that can be operated on either single phase AC or DC power
universal motor
the amount of current drawn when the motor is connected to the maximum load the current is designed to drive
full-load current
the rotating member of a DC generator is called the ___.
armature
the stationary part of an alternator
stator
the horsepower rating for a 3 phase motor is about ____ than a single phase motor of about the same physical size.
150% greater
In split phase motors, when power is first applied, both the run winding and the start winding are energized. When the motor reaches approx ___ of the full speed, the ___ opens, disconnecting the start winding from the ckt.
75% / centrifugal switch
____ motors have the start winding and run winding connected at all times. they do not need a ____ to remove the start winding, thus increasing the running torque.
capacitor- run / centrifugal switch
a switch that opens to disconnect the start winding when the motor reaches a certain preset speed and reconnects the start winding when the speed falls below a preset value
centrifugal switch
the voltage rating that is the optimal voltage that should be connected to a motor for best operating performance
motor nameplate rating
a motor breaking technique when the motor is reconnected as a DC generator after it is disconnected from the main power
dynamic breaking
All AC motors have high initial ___ that can cause breakdown on the power distribution system.
inrush currents
The most common motor used in commercial and industrial applications.
3 phase motor, squirrel cage induction motor
ladder diagrams are read like a book from left to right with ___ on the left and ___ on the right.
input / output
devices that start a load are usually connected in ___ while devices that stop a load are connected in ____.
parallel / series
The part of the ladder diagram that contain control devices such as contact, coils, switches.
rungs
A ___ must be contained in every rung of a ladder diagram.
coil
a device that can sense the force exerted by pressure.
pressure switch
the most common manual operator interface device used in motor control applications is the ___.
push button
often referred to as low voltage release because the lower voltage in the control ckt is switch by the input pilot device. Also called automatic control because no operator action is required for an input signal and activation of the load.
two wire control
the most commonly used motor starter control, requires three wires between the input and the output. sometimes called semi-automatic control because operator action is required to initiate an input signal.
three wire control
a relay which maintains its contacts in the activated state without being continuously energized by means of a mechanical latch or residual magnetism in the coil’s core.
latching relay.
the dc motor is manually started with a ___.
rheostat
____ convert mechanical energy in electrical energy
generators
The most common indicating devices used in a motor control system is the ____.
pilot light
an electronic device for controlling the rotational speed of an AC motor by changing the frequency of the electrical power supplied to the motor.
VFD
Fire alarm initiating devices include:
thermal detectors, duct detectors, smoke detectors, manual switches, and flow switches
Fire alarm notification devices include:
horns, strobes, speakers, and annuciators
Auxiliary control functions include :
fans, door holders, and elevators
Two basic types of of smoke detectors:
ionization and photo electric
Two basic types of thermal detectors:
fixed temperature / rate-of-rise
All initiating and notification devices must be supervised by the ___.
Fire Alarm Control Panel (FACP)
Whether they are manual or automatic, smoke or thermal, flow or tamper, all initiating devices are also considered ___ devices.
monitoring type
For a STRAIGHT PULL, the critical measure of the pull box is its overall length from the raceway entry wall to the raceway exit wall opposite, shall be greater than or equal to __ the trade diameter of the largest raceway being used.
8 times
For an ANGLE PULL, the length and height of the box from the raceway-entry wall to the sidewall opposite must be a minimum of ____ the trade diameter of the raceway.
6 times
the corruption of the fundamental sine wave at frequencies that are multiples of the fundamental.
harmonic distortion
Overheated transformers, neutral conductors, & other electrical distribution equipment, nuisance tripping of ckt breakers, loss of synch on timing ckts that operate on a clean zero crossover sine wave trigger are all symptoms of ____.
harmonic distortion
a high voltage, short duration spike on any of the utility phase conductors.
transient impulse
___ can be as high as several thousand volts and can do tremendous damage to digital equipment. They can be caused by switching operations or weather.
transients
Sophisticated electrical devices that use utility power to synthesize a power source isolated and dedicated to the critical load equipment.
Uninterruptible power supplies
