Motor Controls Test 2
The addition of a control relay to a jogging circuit provides even greater control of the motor drive than the use of a jogging circuit alone.
true
Multiple push-button stations are used to control conveyor motors ____.
. on large shipping and receiving freight docks
How many wires are required for a two-wire control device?
2
If the available power is 208V-3 phase, and the control circuit is wired phase tophase, what is the control voltage? _____ volts.
208
Timed contacts are either normally open or normally closed
true
When a motor must be started and stopped from more than one location, ____.
any number of start and stop buttons may be connected
Electronic Off-delay timers must have power applied ____ topermit the timing circuit to operate
at all times
A selector switch and the automatic pilot device can control a motor directly if their contacts are large enough to pass safely the full-load current of the motor. However, the contact capacity of these devices is usually not large enough for large motors.
true
A triac is used to connect the load to the line in a solid-state relay intended to control an AC load.
true
A two-wire control may be a toggle switch
true
Mechanically held relays are often used in machine tool control circuits.
true
In the case of a(n) ____, the thermal heaters open the overload contacts in the control circuit and de-energize the coil, thus stopping the motor.
overload
What are the applications for a motor-driven timer?
A process that has definite on and off b. A process that has a sequence of successive operations c. A process where infrequent starting of large motors is required d. All of them(Correct Answer) e. both a and b only
What does IEC stand for?
International Electrotechnical Commission
Select the definition of a wiring diagram. (Be thorough!!!)
Is a pictorial diagram. It shows the physical layout of all the equipment and allthe interconnecting wiring.
Electrical symbols usually conform to which standard?
NEMA
Are "ON" control stations used in multiple locations connected in series or parallel for latched-in contactors?
Only for parallel connections for "ON" not for "OFF"
Multiple start buttons are electrically wired in _________
Parallel
Select the definition of a schematic diagram. (Be thorough!!!
Shows the sequence of operation of equipment.
What will happen if the terminals of a blowout coil are reversed?
Theoretically, the motor action of the arc will be in the opposite direction.
What type of device is used to suppress voltage spikes in relay circuits?
Transient suppressor or Metal oxide varistor
The neutral wire can be_______.
White and Light Grey
The movable contact for a normally closed switch is drawn __.
above and touching the stationary contact.
What is the safety feature of a lock-stop push button?
both answers are correct
When a jogging circuit is used, the starter can be energized only as long as the jog button is depressed
true
Schematics show components in their electrical sequence without regard for __.
physical location
Starters, contactors, and ____ are similar in construction and operation
relays
The use of a selector switch in the control circuit to obtain jogging requires a three-element control station with start and stop controls and a ____ switch.
selector switch
Multiple stop buttons are electrically wired in _________
series
Single-pole and double-pole switch symbols are shown as.
single break. b. double break c. all of the above(Correct Answer) d. NO and NC
When there are several timers that meet the requirements of a given application, it is advisable to select the timer with the ____.
smallest number of operating parts
Jogging can be implemented using a ____, two-position selector switch
standard-duty
Mechanical connections are shown with ___.
straight broken lines
The symbol for a __ switch represents a bimetal helix.
temperature
24 volts is the most common control voltage used in an intrinsically safe system
true
A circle is most often used to represent a coil in a motor control schematic, because the letters and/or numbers are written in the circle to identify the coil.
true
Another name for a schematic diagram is an elementary diagram
true
Control magnetic relays are used to controlsmall loads
true
Control relays are small magnetic switches used on simple branch circuits to control complex wiring system operations.
true
Electronic timers have become increasinglypopular in industrial applications.
true
Intrinsically safe systems cannot supply enough energy to ignite the atmosphere in a hazardous location
true
Is the pneumatic timer the most commonly used in industrial applications?
true
It is desirable to extinguish the arc as quickly as possible to keep the contacts cool and this prolong contact life
true
Ladder diagrams are sometimes referred to as elementary diagrams
true
Main or subassembly line conveyors use sequence control.
true
When components are used to perform the function of stop, they are generally wired ____ with the motor starter coil.
normally closed and connected in series
An HOA switch is a two position selector switch
false
An electrician in the field must connect a circuit using a line diagram.
false
In a three-wire control circuit, when the supply voltage returns after a failure, the circuit is re-energized.
false
A flow switch is classified as a pilot device.
true
A control relay is an electrically operated switch.
true
Timers that can be set for multiple functions oras off-delay timers generally plug into ____-pin tube sockets
11
Control systems that operate on ____ volts are often used in hazardous areas
24
Typical control voltages are 120 and ____ volts
24
If the available power is 480/277-3 phase, and the control circuit is wired fromphase to ground, what is the control voltage? _____ volts
277
When reading a schematic diagram?
Are the control components shown as they should be when the machine is turned off or de-energized
Relays are ____________ operated switches.
Electrically
List two (2) other names that are used in place of the term "schematic"
Elementary and Ladder
Why are contactors described as both control pilot devices and large magnetic switches controlled by pilot devices?
Large contactors may be controlled by relays. b. Because of the range in sizes available. c. All answers are correct.(Correct Answer) d. While large contactors can control heavy currents where overload protection is unnecessary or provided separately. e. Small contactors may be used as control devices for larger controls.
Why will the blowout coil also operate on AC
Since the current reverses simultaneously in the blowout coil and arc, the motor action (arc deflection) occurs in the same direction.
What is the first action when the start button of a three-wire control circuit is pushed?
The circuit is completed through the coil.
What are the advantages of a mechanically held relay?
The current is not continually applied to the coils of the relay, thus conserving energy. b. It is absolutely quiet in operation. c. The relay need not be reset when the power returns. d. The circuit continuity is maintained during a power failure. e. All of the above.(Correct Answer)
The motor may be started or stopped from a number of separate stations by connecting all start buttons in parallel and ____ stop buttons in series.
all
Which of the following are factors to be considered when selecting a timing relay for a particular use. a. Allowable error b. Length of time delay required c. Timing range required d. Cycle of operation and reset time e. Cost f. Additional requirements (electrical rating, size, temperature)
all of them
No-voltage protection protects ____.
both the operator and the equipment
When jogging with a control relay on a reversing starter, while the relay is energized, ____.
either the forward or the reverse starter will also remain energized
A "C" on an HOA switch indicates that the contacts are closed and the O indicates that they are open.
false
Anothername for a schematic diagram is a wiring diagram.
false
It is sometimes desirable to operate push buttons or other control devices at some voltage higher than the motor voltage
false
Line diagrams include all of the devices in the system and show the physical relationships between the devices.
false
Magnetic relays are affected by the electricnoise and the voltage spikes induced in the system
false
Neither jogging nor inching prevent a holding circuit.
false
Normally open switches are drawn with the movable contact above and touching the stationary contact
false
Start buttons are electrically wired in series.
false
The control circuit consists of the main contacts and the overload heaters to the motor
false
The greatest advantage of relays with mechanicalcontacts is that they are resistant to shock and vibration
false
The most common coil symbol used in schematic diagrams is the rectangle
false
The operation of each additional push-button control station is different from that of the single push-button control in the basic three-wire circuit.
false
The term inching is often used when referring to across-the-line starters.
false
Two-wire control devices are generally designed to handle large currents
false
The exact timing value for any position within the timing range must be ____.
found by trial and error
Nontimed contacts are controlled directly by thetimer coil, as in a(n) ____ control relay.
general-purpose
The equipment ground can be _______.
green and bare
What conductor can be any color except white, light gray, green or bare?
hot
A three-wire control circuit uses momentary contact, start-stop stations, and a holding circuit interlock connected ____ with the start button to maintain the circuit
in parallel
When a jogging circuit is used, the machine operator has ____ control of the motor drive.
instantaneous
It is necessary to restart a motor after it has been stopped by a three-wire control circuit with ____ protection
low voltage
If set in the ____ position, the coil is connected directly to the power line and the motor will run continuously.
on
If the HOA switch is set in the off position, ____ current can flow to the coil of the starter.
on
When the switch is set in the hand position, contacts 1 and 2 are closed, and contacts 3 and 4 are ____.
open
The operation of the overload protection ____ the control circuit.
opens
Two-wire control ____.
provides no-voltage release or low-voltage release
One of the most used symbols in control schematics is the ________.
push button
A mechanically held or latching relay is operated by electromagnets.
true
Electrical symbols are shown in the de-energized position on Schematic diagrams
true
For troubleshooting purposes, it is better to use a schematic diagram; instead of awiring diagram.
true
Mechanically held relays are energy-saving devices because the coils are energized only momentarily and not continuously.
true
Most of the relays used in machine tool controlhave double-break contacts.
true
Pilot lights are tested frequently to ensure operation
true
Pilot lights are used for safety and communication.
true
Pneumatic timers have good repeat accuracy.
true
Pressing any stop button de-energizes the coil.
true
Relays are used more often to open and closecontrol circuits than to operate power circuits.
true
Schematics are always drawn to show components in their de-energized or off state
true
Selector switches often contain multiple sets of contacts.
true
Sequence control exists when starters are connected so that one cannot be started until the other is energized
true
Sirens, horns, and loud buzzers may be used in production systems to call attention to malfunctions
true
The conventional three-wire, push-button control circuit may be extended by the addition of one or more push-button control stations.
true
The larger contactor sizes are used to provide remote control of relatively high-current circuits where it is too expensive to run the power leads to the remote controlling location
true
The most standardized set of symbols in the U.S. is provided by the NEMA.
true
The motor action established by the magnetic fields of the blowout coil and the arc plus the use of arc deflectors or arcing horns cause the arc to Lengthen and move upward.
true
The principal difference between a contactor and a motor starter it that a motor starter contains overload relays and a contactor does not.
true
Three-wire control prevents the restarting of machinery when power is restored.
true
Timing Relays can come equipped with timing contacts and instantaneous contacts.
true
Timing relays are used for any application wherethe operating sequence requires a delay
true
Two-wire controls may be connected to operating coils of magnetic switches
true
When configuring separate control wiring, the maintenance technician must ensure that the proper connections are made.
true
When the load side of the circuit is separated from the control side by a light beam it is called optoisolation
true
You should never wire in a set of normally closed contacts in a series with thecoil of the same device.
true
The selector switch is controlled by ____ the push button sleeve.
turning
Which of the following factors will affect the selection of a timing relay. a. Type of power supply b. contact ratings c. timer contact arrangement d. temperature range e. dimensions
all of them
Sequence control is required whenever the ____ must be operating before the machine itself can be operated safely.
auxiliary equipment associated with a machine
Jogging is defined by ____ as "the quickly repeated closure of a circuit to start a motor from rest for the purpose of accomplishing small movements of the driven machine."
nema
A hand-off automatic switch may be a stand alone control or incorporated into a start-stop push button station.
true
A pneumatic timer is adjusted by positioning a needle valve to vary the degree of orifice restriction.
true
A power transistor is used to connect the load to the line in a solid-state relay intended to control a DC load.
true
A selector push button can be used to obtain jogging
true
An advantage of using a two-wire control device is because automatic controls may be used to control a motor or an operation without requiring the presence of an operator.
true
Motors draw half as much current on high voltages as they do on low voltages
true
