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119 Cards in this Set

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  • Back
when the terminals on a control transformer have to be linked by wire, the ____ wire types and sizes should be used.
manufacturer recommended
To step down from 480 v ac to 120 v ac, the primary windings are connected in _______ and the secondary windings are connected in ____________.
Series
Parallel
Control transformers are rated in ....
VA Volt Ampere.
Generally, control transformers step down the main line voltage to a control voltage of _______ or ______V AC
_120
_24v ac
The wiring terminals of a control tranformer are connectred together witha metal clip to minimize the __________.
VOLTAGE DROP
The NEMA standard specifies that ac magnetic motor starting devices must funtion at voltages as loq as >>>>>>>>>>> of ther rated coil voltage.
85%
Control transformers generally have overcurrent protection provied by _______ or _______.
Fuse or Circuit breakers
List three common installation configuration options for control transformer fuse blocks
fuse clips
fuse holders
DIN rail mounted.
Some industrial application require fuse protection on one ______ line and in both _______ lines.
Secondary
Primary
the use of fuses on the primary and secondary side of a control tranformer is specified by the
NEC
AC ckts of ____________V or more must be grounded in accordance with the NEC section 250.
50
The ___________ system is the most common for industrial control applications.
grounded
Voltage measurements should be made in the _______ condition and the _______ load condition.
no load full load
Early example of a motor controller
Knife Switch
Difference between a contactor and a motor starter
starter has overloads
three factors for discontinuing use of knife switch to control motors
hitting contacts
mechanical failure
contact damage
Pilot devices used with manual motor starters are restricted to _______ operations and are connected in ________ with the line or load circuits.
singles phase
series
using pilot devices with maintined contacts to control a motor starter is known as ________ control
2 wire
Fuses and breakers protect what part of the motor ckt
conductors
although knife witches are no longer used as motor controllersk a modern version of the knife witch can be found in what device.?
disconnect switch
double break contacfts are used instead of single break... why>
arcing is reduced
what material is used on the surface of most starter contacts?
Silver
why are contact surfaces curved?
better connection
self cleaning
name three types of contacters other than motor starters
magnetic contactor
definite purpose magnetic contactor
manuel contactor
which type of magnetic contactor has the options to keep the contacts pulled in when power to the coil is remove?
definite purpose magnetic contactor
three types of contacts fouind on contactors
NO
NC
Auxillary
a lihgting load which has a continuoius current ratring of 250 amperes is to be controlled using a magnetic contactor. what size nema contactor would be required for this load???
SIZE 5
what is the maximum size of motor which can be controlled using size 2 nema contactor???
25 HP
what class of IEC contactor is used to control a motor when starting plugging and inching are typical operations required for the control of this motor
AC 4 squirrel cage starter
if you were replacing an AC-3, 23 A IEC contactor with a nema contactor what sizwe contactor would bne required???
size 2
arc chutes are designed to quench the arc by ____, ____ and ____ the arc produced by each set of contacts./
devide confine extinguish
the most common definite use contactor is the _______ contactor
lighting
What is the difference between a contactor and a motor starter???
contactors are with out an overload protective device.
what is a magnetic motor starter?
electromechanical device provides a means to start and stop the motor.
List some common examples of typical fractional horspower motors that would be controlled by manual motor starters.
exhaust fan, small drill, presses and commercial garbage disposals, blower motors small pumps.
overlaod relys protect what part of the motor circuit.?
THE MOTOR
THE NEC requires a motor controller to perform what two functions?
disconnect power to the motor
provide overload protection
why cant fuses and breakers be used to protect from overloads
because of inrush current.
the damage to a motor caused by an overload is proportional to what two factors?
magnitude
duration
what is the main fuction of an overload relay>?
detects excessive over-current conditions in the motor by measuring motor current
the three overloads (heaters) are ________ connected in series with the motor, but are _______ connected to a single normally closed overload contact in the control circuit ,
electrically
mechanically
what are the three types of overload relays?
Thermal (heat)
magnetic
electronic
what is the cause of most motor failures?
HEAT
all overlaod relays muyst have a way to ________ once the overload condition has been corrected
reset
list the parts of a thermal overlaod relay
heater
contacts
reset button
how are the main motor contacts of a magnetic starter closed?
an electromagnetic solenoid
the most common of the melting alloy type heaters is comprised of what basic parts?
eutectic alloy
2 types of thermal overload relays
melting alloy
bi-metallic
what limits the size of a magnetic motor starter?>
as motor current increases the size of the starter contact increaes
a 500 horspower three-phase motor operates at 480 v ac,. what size NEMA starter is needed for this application
7
a three hp single phase motor operates at 120 v ac, what size NEMA starter is needed
2
a 25 hp 3 phase motor operates at 208 vac what size nema is needed
3
how is a bi metallic overload relay contructed?
2 pieces expand and contract at different rates
difference between nema and iec starters.?
nema - no auto reset
iec needs provision to adjust
what three factors are considered when rating an IEC motor starter?
operational current
thermal current
utilization catagory
disadvantages of bi metallic overload relay
automatic restart
why is lower control voltage often used with thigh voltage motors?
safety
less expensive
two advantages to using magnetic overload relays
great flexibility
quicker reset time
no heat to operate
what has allowed magnetic motor starters to replace manual motor starters in most commercial and industrial applications?
flexibility and intergration
list five advantages to using electronic overload relays rather than thermal or magnetic overload relays.
low energy consumption time
instantaneous resets
low energy consumption
faster reaction time
instant phase loss protection
list two common controll voltages used for ac magnetic motor starter coils
120 v 24 v
describe the operation of an electronic overload relay
small current tranformer monitors current use
most thermal and magnetic overload relays are connected in __________ with the motor power ckt, so all ________ flowing to the motor must flow through the overload
series
current
in addition to main motor contacts, many starters have additional sets of contacts known as _____ or _____ for use in the control circuit
auxillary contacts
electrical interlock
contact configurations available for auxillary contacts
no
nc
no/nc
what is an integral motor protection device?
thermal switch inside motor housing senses heat generated by motor
two inherant motor protection devices
bi metallic thermal disk
thermister
what is a combination starter>
consists of a magnetic starter and disconnect switch mounted on the same enclosure
2 reasons timing ckts are used in moroe control applications
eliminate the labor intensive effort of manually controlling the time of each process operation

they reduce the need for multiple machine operations
timers are devided into categories based upon what?
how they control the timing
types of functions performed
list three basic methods that timers use to manage timing
dashpot controlled
clock timer
solid state timer
what types of timing functions are mechanical timers capable of?
on-delay
off- delay
what applications are clock timers best suited for?
produiction systems
what does the abbreviation DOE stand for to timers>
delay on energy
explain DOE timing and state when the contacts chanfe state?
the delay starts when the timer is activated and the our put contacts change after the delay.
what are the two basic categories of dashpot timers?
pneumatic style (air)
fluid style
how is timing managed in a dashpot timer
by controlling the rate of fluid though a contricted orifice
what is the typical timing accuracy of a pneumatic dashpot timer
within a few seconds
2 reasons timing ckts are used in moroe control applications
eliminate the labor intensive effort of manually controlling the time of each process operation

they reduce the need for multiple machine operations
timers are devided into categories based upon what?
how they control the timing
types of functions performed
list three basic methods that timers use to manage timing
dashpot controlled
clock timer
solid state timer
what types of timing functions are mechanical timers capable of?
on-delay
off- delay
what applications are clock timers best suited for?
produiction systems
what does the abbreviation DOE stand for to timers>
delay on energy
explain DOE timing and state when the contacts chanfe state?
the delay starts when the timer is activated and the our put contacts change after the delay.
what are the two basic categories of dashpot timers?
pneumatic style (air)
fluid style
how is timing managed in a dashpot timer
by controlling the rate of fluid though a contricted orifice
what is the typical timing accuracy of a pneumatic dashpot timer
within a few seconds
2 reasons timing ckts are used in moroe control applications
eliminate the labor intensive effort of manually controlling the time of each process operation

they reduce the need for multiple machine operations
timers are devided into categories based upon what?
how they control the timing
types of functions performed
list three basic methods that timers use to manage timing
dashpot controlled
clock timer
solid state timer
what types of timing functions are mechanical timers capable of?
on-delay
off- delay
what applications are clock timers best suited for?
produiction systems
what does the abbreviation DOE stand for to timers>
delay on energy
explain DOE timing and state when the contacts chanfe state?
the delay starts when the timer is activated and the our put contacts change after the delay.
what are the two basic categories of dashpot timers?
pneumatic style (air)
fluid style
how is timing managed in a dashpot timer
by controlling the rate of fluid though a contricted orifice
what is the typical timing accuracy of a pneumatic dashpot timer
within a few seconds
2 reasons timing ckts are used in moroe control applications
eliminate the labor intensive effort of manually controlling the time of each process operation

they reduce the need for multiple machine operations
timers are devided into categories based upon what?
how they control the timing
types of functions performed
list three basic methods that timers use to manage timing
dashpot controlled
clock timer
solid state timer
what types of timing functions are mechanical timers capable of?
on-delay
off- delay
what applications are clock timers best suited for?
produiction systems
what does the abbreviation DOE stand for to timers>
delay on energy
explain DOE timing and state when the contacts chanfe state?
the delay starts when the timer is activated and the our put contacts change after the delay.
what are the two basic categories of dashpot timers?
pneumatic style (air)
fluid style
how is timing managed in a dashpot timer
by controlling the rate of fluid though a contricted orifice
what is the typical timing accuracy of a pneumatic dashpot timer
within a few seconds
a part of the pneumatic dashpot that air enters of leaves during the timing function is called a
bellow
Pneumatic timers have narrow trimming ranges with settings from ______ to ______ seconds
.1 to 180
Pneumatic timers are most accurate near their ______ range.
MEDIAN
what does the abbreviation DODE stand for>
delay on de-energized
explain why fluid type dashpot timers are more accurate than pnuematic dashpot timers
because the oil desinity is only affected by temperatuire
motor control drawings show their components in what state?
de-energized "on the shelf"
dashpot timers use ____ to initiate the timing process.
air or oil
dashpot timers can be configured with contacts that are normally _____ or normally ____
open closed
when dashpot timing assemblies are attached to a control relay, the entire mechanism is generally referred to as a
timer
besides the timed contacts, what other connections are required for a solid state DODE timing relay?
external trigger
voltage input