Chapter 2 Homework
NEMA requires that motors be able to carry their rated horsepower at nameplate voltage plus or minus
10%
In general operation motors are classified according to the type of power being used as being ___or ___
AC, DC
The duty cycle of a motor is listed on the nameplate as __________ or __________.
CONT, INTER
The phase rating of a motor is listed on the nameplate as ___,____, or ____
DC, 1-phase, 3-phase
The motor nameplate Code letter specifies the locked rotor current rating of the motor in:
KVA per HP
The abbreviation most used for a pushbutton switch is ________.
PB
The three distinct windings of a three-phase motor are referred to as:
Phase A, Phase B, Phase C
The IEC nomenclature for the output leads of a 3-phase motor are identified as __________.
U - V - W
With "low voltage protection" on motor controls
a power failure disconnects service and when power is restored manual restarting is required
The motor nameplate __________ temperature rating is the maximum rated temperature of the air surrounding the motor.
ambient
The plugging of a motor refers to
braking by reverse rotation.
The device used to automatically disconnect the starting winding of a single-phase split-phase motor is called a __________ switch.
centrifugal
The two basic parts of a typical motor circuit are the
control circuit and power circuit.
When a dual-voltage motor is operated at the HIGHER voltage rating the operating
current is lower
For six-lead dual voltage 3-phase motors the 3-phase configuration used for the low voltage is ___ and for high voltage is ____
delta, wye
On electrical diagrams, conductors that cross each other and make contact are represented by a heavy __________ at the junction.
dot
A pressure switch would be classified as a load.
false
When more than one electrical load is connected in a rung of a ladder diagram, the loads are normally connected in series.
false
When replacing a motor, selecting the same __________ ensures that the mounting mechanism and hole positions will match.
frame size
The speed of an AC induction motor depends on the __________.
frequency of the electrical power supply and the number of poles built into the motor
Inverter-duty describes a class of motors that are capable of operation
from a variable frequency drive
Which of the following types of motor starters connects the motor directly to the supply line on starting?
full voltage starter
In a ladder diagram, the electrical components are arranged according to their ____ in the circuit.
function
Additional START or ON control devices are wired
in parallel
The __________ is the electrical device in a ladder diagram that uses the power supplied from L1 to L2.
load
Two-wire control circuits use a __________-contact type of control device.
maintained
Three-wire control circuits use a __________-contact type of control device.
momentary
A motor nameplate indicates that the motor has a "service factor" of 1.25. This means that the
motor can on occasion safely develop 125% of its rated HP
Information required to identify a motor is contained on the motor __________.
nameplate
The two general classifications of motor enclosures are __________ and __________.
open, totally enclosed
For a __________ connection of loads, the voltage across load is the same as that of the applied voltage.
parallel
On a ladder diagram, a rung is defined as a complete _____ from L1 to L2 that contains a load.
path
A wiring diagram is intended to show the actual ____ of all components
physical location
With a "selector switch" a
plunger actuates the contacts
The circuits on most motor control schematics can be broken down into being part of the __________ circuit or the __________ circuit.
power, control
The rotating part of an AC motor is referred to as the __ and the stationary part is called the ___
rotor, stator
A ladder diagram is a(n) ____ representation of an electric circuit.
schematic
In a dual-voltage split-phase motor, the two run windings are connected in __________ for the HIGH voltage operation.
series
Which of the following diagrams shows an electrical installation reduced to its simplest form?
single-line diagram
Industrial applications use DC motors because the ____/ ____ relationship can be easily varied
speed, torque
A "motor starter" is an electric controller used to __________ a connected motor
start, stop, and protect
The amount the motor winding temperature will increase above the ambient at full load is specified according to the nameplate __________ rating.
temperature rise
The motor term "auxiliary contact" refers to
the contact of a switching device in addition to the main circuit contact.
Ladder diagrams show
the electrical connections
On a block diagram the arrows connecting the blocks indicate
the general direction of current paths
The nameplate of a motor indicates that it is thermal protected. This means __________.
the motor has a built-in thermal device
A fuse is never placed on the grounded side of the circuit.
true
A squirrel cage rotor has no physical electrical connection to it.
true
Three-phase motors are self-starting on their running windings.
true
When conductors cross but make no electrical contact, this is represented intersecting lines with no dot.
true
For a six-lead dual voltage with a low voltage rating of 220 volts, the high voltage rating would be
380 volts
Single-phase motors are
all of these
The line frequency of a motor is abbreviated on the nameplate as:
all of these
Standard NEMA motor insulation classes are given by:
alphabetic classification (A, B, F, H, etc.)
A conduit layout diagram normally does not include the number and size of wires to be run in the conduit.
false
A motor with a low power factor rating will draw less current for the same horsepower than a motor with a high power factor.
false
If a control circuit is supplied from a grounded circuit, it makes no difference what side of the line is grounded.
false
In a ladder diagram, components are arranged according to their physical position in the installation.
false
The HP nameplate rating of a motor is a measure of the full load output power the shaft of the motor can produce without stalling.
false
The conductors feeding current to a large motor would be part of the control circuit.
false
The heavier lines on electrical diagrams usually indicate the control circuit conductors.
false
The nameplate efficiency value of a motor is its efficiency rating with no load applied to the motor.
false
The rated nameplate speed of a motor is its approximate speed with no load applied.
false
The single-line diagram uses blocks along with a single-line to show all the major components of a system.
false
The use of DC motors is more widespread than the use of AC motors.
false
Two-wire control circuits are designed to protect against automatic restarting when power returns after a power failure.
false
When a split-phase motor is operated with a capacitor in series with one of the stator windings the
starting torque is higher
On a ladder diagram, all wires that connect to a common point are assigned __________.
the same numbers
All 3-phase motors are wired so that the phases are connected in either Wye or Delta configuration.
true
All electrical components are normally drawn in the off-state or de-energized position.
true
At least one load must be included in each rung of a ladder diagram.
true
Broken lines on a diagram are usually used to show mechanical connections.
true
Dynamic braking can be used with DC motors to bring the motor to a stop without the aid of a mechanical brake.
true
Magnetic motor starters allow a motor to be controlled from a remote location.
true
Motor terminal markings are usually used to tag only those terminals to which connections must be made from external circuits.
true
Nine-lead dual 3-phase motors have a 2-to-1 voltage difference.
true
No wires or components are normally shown on block diagrams.
true
Single-phase AC motors are typically constructed in small horsepower sizes.
true
Symbols for electrical devices may not always resemble the real thing.
true
The direction of rotation of a DC motor depends on the direction of the magnetic field and the direction of the current flow through the armature.
true
The motor nameplate Design letter is an indication of the motor's torque speed curve.
true
Wires common to each other are usually identified by the same number.
true
Wiring diagrams are used when installing and tracing wires in electrical installations.
true
With low-voltage protection, when power is restored after a power failure, manual restarting is required.
true
You can reverse the direction of rotation of a 3-phase motor by reversing any two of the three main power leads to the motor.
true
To differentiate between NO and NC contacts on a ladder diagram, NC contacts are identified as a number which is
underlined