Motor Controls Practice Exam 3
Timers that can be set for multiple functions or as off-delay timers generally plug into ____-pin tube sockets
11
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 to phase, what is the control voltage? _____ volts.
208
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 from phase to ground, what is the control voltage? _____ volts.
277
In an autotransformer-type starter, autotransformers supply ____of the line voltage to the motor.
65%
The movable contact for a normally closed switch is drawn __.
Above and touching the stationary contact.
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
When a motor must be started and stopped from more than one location, ____.
Any number of start and stop buttons may be connected
When reading a schematic diagram?
Are the control components shown as they should be when the machine is turned off or de-energized?
Of the two types of electrical interlocks used in industry, which type is the most common one used?
Auxiliary contact interlock
Sequence control is required whenever the ____ must be operating before the machine itself can be operated safely.
Auxiliary equipment associated with a machine
No-voltage protection protects ____.
Both the operator and the equipment
DPDT
Double-Pole Double-Throw
DPST
Double-Pole Single-Throw
Relays are ____________ operated switches.
Electrically
List two (2) other names that are used in place of the term "schematic".
Elementary and ladder
A "C" on an HOA switch indicates that the contacts are closed and the O indicates that they are open.
False
A reversing starter usually consists of two (2) contactors and two (2) overload relays.
False
An HOA switch is a two position selector switch.
False
An electrician in the field must connect a circuit using a line diagram.
False
Another name for a schematic diagram is a wiring diagram.
False
In a three-wire control circuit, when the supply voltage returns after a failure, the circuit is re-energized.
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 electric noise and the voltage spikes induced in the system.
False
Push-button interlocking is an electrical method of preventing both starter coils from being de-energized simultaneously.
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 the timer coil, as in a(n) ____ control relay.
General-purpose
The equipment ground can be _______.
Green or bare.
If set in the ____ position, the coil is connected directly to the power line and the motor will run continuously.
Hand
Reversing starters are available in ____ construction.
Horizontal and vertical
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
The term interlocking is used generally when referring to motor controllers and control stations that are ____ to provide control of production operations.
Interconnected
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 all the interconnecting wiring.
It is necessary to restart a motor after it has been stopped by a three-wire control circuit with ____ protection
Low-voltage
Reversing starters consisting of mechanical and electrical interlocked devices are preferred for ____.
Maximum safety
Electrical symbols usually conform to which standard?
NEMA
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
NC
Normally Closed
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
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"
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
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
Multiple start buttons are electrically wired in ___.
Parallel
Schematics show components in their electrical sequence without regard for ____.
Physical location
Starting transformers momentarily affect the ____.
Power factor
Two-wire control ____.
Provides no-voltage release or low-voltage release
One of the most used symbols in control schematics is the _____.
Push button
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
Multiple stop buttons are electrically wired in ____.
Series
Select the definition of a schematic diagram. (Be thorough!)
Shows the sequence of operation of equipment
Contact surfaces are generally a ____ alloy for better electrical conductivity.
Silver
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.
SPDT
Single-Pole Double-Throw
SPST
Single-Pole Single-Throw
Two-pole starters are used for ____.
Single-phase motors
Current transformers are used on large motor starters to step down the current so that a conventional overload relay and heater ____ may be used.
Size
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
If magnetic control devices are to be used, then reversing ____ accomplish the reversal of the motor direction.
Starters
The symbol for a __ switch represents a bimetal helix.
Temperature
After the forward coil has been energized, is the auxiliary forward interlocking contact open or closed?
The forward interlock is open.
The neutral wire can be_______.
White or light grey.
In industry, when looking directly at the two types of reversing starters, which contactor on both types is usually the forward contactor? (BE SPECIFIC!)
Top & left
What type of device is used to suppress voltage spikes in relay circuits?
Transient suppressor or Metal oxide varistor
24 volts is the most common control voltage used in an intrinsically safe system.
True
A flow switch is classified as a pilot device.
True
A hand-off automatic switch may be a stand alone control or incorporated into a start-stop push button station.
True
A mechanical interlock can be used on a reversing starter whenever an electrical system is used.
True
A mechanically held or latching relay is operated by electromagnets.
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
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
All overload relays must allow some period of time before tripping to allow the motor to start.
True
An overload relay consists of overload heaters and overload contacts.
True
Another name for a schematic diagram is an elementary diagram.
True
Electrical interlocks are usually mounted on the side of a motor starter.
True
Electrical symbols are shown in the de-energized position on schematic diagrams.
True
Electronic timers have become increasingly popular in industrial applications.
True
Fuses and Circuit Breakers are used for short circuit protection.
True
Interlocking is obtained by normally closed auxiliary contacts on the forward and reverse contactors of the starter.
True
Intrinsically safe systems cannot supply enough energy to ignite the atmosphere in a hazardous location.
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
Magnetic overload relays are used on large reduced voltage starters.
True
Magnetic starters can be controlled remotely.
True
Main or subassembly line conveyors use sequence control.
True
Mechanically held relays are energy-saving devices because the coils are energized only momentarily and not continuously.
True
Mechanically held relays are often used in machine tool control circuits.
True
Most of the relays used in machine tool control have double-break contacts.
True
Motors draw half as much current on high voltages as they do on low voltages.
True
Nothing will happen if both the forward and reverse push buttons were pushed at the same time on a reversing control circuit because the push button starting circuit is broken by both normally closed contacts in the push buttons.
True
Pilot lights are tested frequently to ensure operation.
True
Schematics are always drawn to show components in their de-energized or off state.
True
Seal-in contacts are required in pushbutton interlock control circuitry.
True
Sequence control exists when starters are connected so that one cannot be started until the other is energized.
True
The NEC® requires that each phase of a motor be protected by an overload relay.
True
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
The conventional three-wire, push-button control circuit may be extended by the addition of one or more push-button control stations.
True
The direction of rotation of three-phase motors can be reverse by interchanging any two motor leads to the line.
True
The direction of rotation of three-phase motors can be reversed by interchanging any two-motor leads to the line.
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 pneumatic timer is the most commonly used in industrial applications.
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
The purpose of interlocking is to prevent contactors from being energized simultaneously or closing together; in this way, short circuits are avoided.
True
Timed contacts are either normally open or normally closed.
True
Timing Relays can come equipped with timing contacts and instantaneous contacts.
True
When a jogging circuit is used, the starter can be energized only as long as the jog button is depressed.
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 opto-isolation.
True
With automatic sequence control, a series of motors can be started automatically with only one (1) start-stop control station.
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 are factors to be considered when selecting a timing relay for a particular use?
1) Allowable error 2) Length of time delay required 3) Timing range required 4) Cycle of operation and reset time 5) Cost 6) Additional requirements (Electrical rating, size, temperature)
Single-pole and double-pole switch symbols are shown as
1) Double-break 2) Single-break 3) NO and NC
If a mechanical interlock is the only means of interlocking used, what procedure must be followed to reverse the direction of the motor? Assume the motor to be running forward.
The stop button must be pressed before any reversal of direction can take place.
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.
Define interlocking control.
Used to prevent two coils from energizing at the same time possibly causing a short circuit.
What are the applications for a motor-driven timer?
1) A process that has definite on and off 2) A process that has a sequence of successive operations 3) A process where infrequent starting of large motors is required
What are the limitations for using pushbutton interlocking in industry? For example, what type of load can be controlled and what range of horsepower can pushbutton interlocking be used with?
1) Five horsepower and below 2) Low torque loads
What is the safety feature of a lock-stop push button?
1) Lock stops open only the control circuits and provide safety to workers who may be injured while working on a machine if it is started suddenly 2) A stop button of a control circuit can be padlocked in the off position; thus, it is difficult for anyone to start a machine. This procedure is similar to pulling a safety disconnect switch and locking it in the off position
If pilot lights are to indicate which coil is energized, where should they be connected? Additional auxiliary contacts are not to be used..
1) The "forward" indicating light should be connected in parallel with the "forward" coil (across the coil) to receive full voltage when the coil is energized. 2) The "reverse" light should be connected in a similar manner to the reverse coil.
What are the advantages of a mechanically held relay?
1) The relay need not be reset when the power returns. 2) It is absolutely quiet in operation. 3) The current is not continually applied to the coils of the relay, thus conserving energy. 4) The circuit continuity is maintained during a power failure.
____ overload relays react only to current excesses and are not affected by temperature.
Magnetic
List the two type of reversing starters.
Vertical and Horizontal
The control circuit consists of the main contacts and the overload heaters to the motor.
False
The greatest advantage of relays with mechanical contacts 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
NO
Normally Open
Electronic Off-delay timers must have power applied ____ to permit the timing circuit to operate.
At all times
A mechanical interlocking device is assembled at the factory ____ the forward and reverse contactors.
Between
Which of the following factors will affect the selection of a timing relay?
1) Type of power supply 2) Contact Ratings 3) Timer contact arrangement 4) Temperature range 5) Dimensions
Why are contactors described as both control pilot devices and large magnetic switches controlled by pilot devices?
1) While large contactors can control heavy currents where overload protection is unnecessary or provided separately. 2) Because of the range in sizes available 3) Large contactors may be controlled by relays 4) Small contactors may be used as control devices for larger controls
If the HOA switch is set in the off position, ____ current can flow to the coil of the starter.
No
Multiple push-button stations are used to control conveyor motors ____.
On large shipping and receiving freight docks
Two-wire controls may be connected to operating coils of magnetic switches.
True
Timing relays are used for any application where the operating sequence requires a delay.
True
How is a change in the direction of rotation of a three-phase motor accomplished?
By interchanging any two motor leads to the line.
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
Auxiliary contact interlocking is accomplished by wiring normally open auxiliary contacts of one contactor in series with the other contactor coil.
False
Most motors are successfully started at 90 percent of line voltage.
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
Overvoltage produces low coil currents.
False
Pushbutton interlocking is an electrical method that allows both starter coils to energize at the same time.
False
Start buttons are electrically wired in series.
False
The term inching is often used when referring to across-the-line starters.
False
Starters, contactors, and ____ are similar in construction and operation.
Relays
Mechanical connections are shown with ___.
Strait broken lines
What is the first action when the start button of a three-wire control circuit is pushed?
The circuit is completed through the coil.
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
A control relay is an electrically operated switch.
True
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
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
Control magnetic relays are used to control small loads.
True
Control relays are small magnetic switches used on simple branch circuits to control complex wiring system operations.
True
For troubleshooting purposes, it is better to use a schematic diagram instead of a wiring diagram.
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
Pushbutton and auxiliary contact interlocking are classified as electrical interlocks.
True
Relays are used more often to open and close control circuits than to operate power circuits.
True
Selector switches often contain multiple sets of contacts.
True
Sirens, horns, and loud buzzers may be used in production systems to call attention to malfunctions.
True
Three-wire control prevents the restarting of machinery when power is restored.
True
