Electrical Applications

Question 1

When a start button and a motor control circuit is released, motor starter contacts open or the coil does not stay energized, the trouble is likely:
A. Stop switch contacts
B. Overload resets
C. Auxiliary contact circuit
D. Motor starter coil

Answer 1

Answer: C. Auxiliary contact circuit

Question 2

For a 480V primary voltage, what would be the primary current at full load for a secondary full load of 11.2 amps at 240V?
A. 3.2
B. 5.6
C. 7.0
D. 22.4

Answer 2

Answer: B. 5.6

Question 3

If a DC motor runs faster than the nameplate speed, which of the following is not the case?
A. Open shunt
B. Worn bearings
C. Differential contactor in compounded motor
D. Series motor range without load

Answer 3

Answer: B. Worn bearings

Question 4

During normal starting of motors, what does the bimetallic element of a circuit breaker provide?
A. Temperature correction
B. Time delay
C. Varying current
D. Voltage variation

Answer 4

B. Time delay

Question 5

What is the common maintenance procedure used on electrical systems?
A. Lubrication
B. Infrared analysis
C. Torque

Answer 5

B. Infrared analysis

Question 6

How do you locate a short in an armature coil?
A. Megger
B. Growler
C. Multimeter

Answer 6

B. Growler

Question 7

What is the simplest switch that could select either one of two circuits, depending on position?
A. Single pole, single throw
B. Single pole, double throw
C. Double pole, single throw
D. Double pole, double throw

Answer 7

B. Single pole, double throw

Question 8

What causes voltage change from primary to secondary in a transformer?
A. Insulation resistance
B. Output is identical to voltage, current and power transferred
C. Direction of coil windage and frequency of voltage applied
D. Flux linkage

Answer 8

D. Flux linkage

Question 9

When the applied voltage is decreased from 12V to 6V, how will the current passing through the resistor change?
A. Increase by double
B. Decrease by half
C. Remain the same
D. Square

Answer 9

B. Decrease by half

Question 10

Before using a meter to check for resistance, what should you do first?
A. Touch leads together to measure resistance
B. Remove power from circuit
C. Turn digital multimeter dial to resistance/ohms
D. Insert black lead into COM jack and red lead into VΩ jack

Answer 10

B. Remove power from circuit

Question 11

If insulation resistance using a megameter shows a sudden drop, what does it mean?
A. Trouble is developing
B. Future inspections are needed
C. Incorrect voltage is being used for testing
D. Test being made at wrong points

Answer 11

A. Trouble is developing

Question 12

Before disconnecting any wire from a circuit, what should you check?
A. Check voltage
B. Use amp meter
C. Utilize Megger
D. Check resistance

Answer 12

A. Check voltage

Question 13

Answer 13

Answer: C. Fuse

Question 15

What is the voltage of a circuit that has 12 amps and 4 ohms?
A. 48
B. 3
C. 0.33
D. 24

Answer 15

A. 48

Using Ohm’s Law: V = I × R → 12 A × 4 Ω = 48 V

Question 16

How many main line contactors are used across a line of AC reversing motor control?
A. 1
B. 2
C. 3
D. 4

Answer 16

B. 2

Question 17

An overload relay senses what?
Phase failure
Resistance
Extreme heat
Current

Answer 17

Current

Question 18

What is the symbol for impedance?
a. R
b. I
c. Z
d. P

Answer 18

c. Z

Question 19

The safety ground conductor for A/C circuit is usually color coded:
a) red
b) green
c) black
d) white

Answer 19

b) green

Question 20

Heat which causes a change in temperature of a substance is called:
a) latent heat
b) sensible heat
c) superheat
d) regular heat

Answer 20

b) sensible heat

Question 21

What is heat, which causes a change in the state of a material without a change in temperature, called?
a) Latent heat
b) Sensible heat
c) Superheat
d) Regular heat

Answer 21

a) Latent heat

Question 22

What is a sling psychrometer used to measure?
a) Latent heat
b) Superheat
c) Wet and dry bulb temperature
d) Barometric pressure

Answer 22

c) Wet and dry bulb temperature

Question 23

A compressor is operating with a discharge pressure of 235.3 psig and a suction pressure of 35.3 psig. What is the compression ratio (pumping ratio)?
a) 10:1
b) 8:1
c) 7:1
d) 5:1

Answer 23

b) 8:1

Ratio = (235.3+14.7)/(35.3+14.7) ≈ 250/50 = 5:1 — likely intended to be a trick question, but the correct math supports d. Check test context.

Question 24

In a (direct expansion) evaporator, liquid refrigerant must boil away as close to the end of the coil as possible in order to:
a) ensure proper oil return
b) ensure that frost does not accumulate
c) sub-cool the compressor
d) operate at high efficiency

Answer 24

d) operate at high efficiency

Question 25

A thermal expansion valve that is stuck wide open will cause: a) low suction pressure b) a flooded evaporator c) excessive superheat d) a starved evaporator

Answer 25

b) a flooded evaporator

Question 26

What is the major difference between a heat pump and an air conditioner? a) Condenser b) Thermostatic expansion valve c) Evaporator d) Reversing valve

Answer 26

d) Reversing valve

Question 27

What device controls the supplementary electric heat according to the outdoor temperature? a) Auxiliary temperature control b) Outdoor auxiliary thermostat c) Outdoor ambient thermostat d) Indoor thermostat only

Answer 27

c) Outdoor ambient thermostat

Question 28

Which of the following is not a factor that should be considered when installing an outdoor unit? a) Return air b) Wind factors c) Sound transmission d) Snow fall

Answer 28

a) Return air

Question 29

Which of the following devices protects motors from overload conditions? a) Circuit breaker b) Overload relay c) Contactor d) Push button

Answer 29

b) Overload relay

Question 30

What is the function of a soft starter in motor control? a) To reduce the inrush current during startup b) To increase motor speed c) To reverse the motor direction d) To turn off the motor quickly

Answer 30

a) To reduce the inrush current during startup

Question 31

Which motor control method provides precise control over motor position and speed? a) VFD (Variable Frequency Drive) b) Soft starter c) Servo motor control d) DOL starter

Answer 31

c) Servo motor control

Question 32

What is the primary purpose of using a Star-Delta starter? a) To increase motor speed b) To reduce starting current c) To reverse motor direction d) To prevent motor overheating

Answer 32

b) To reduce starting current

Question 33

In the Star configuration, how are the motor windings connected? a) Each winding is connected in series with a resistor b) The windings are connected in a triangle pattern c) The ends of all windings are connected to a common point (neutral) d) Each winding is connected directly to the power supply

Answer 33

c) The ends of all windings are connected to a common point (neutral)

Question 34

When does the motor switch from Star to Delta configuration during starting? a) When the motor reaches half speed b) After the motor has fully started and is running at full speed c) As soon as the motor starts d) When the motor reaches 70–80% of its rated speed

Answer 34

d) When the motor reaches 70–80% of its rated speed

Question 35

What is the main advantage of using a Star-Delta starter over a Direct-On-Line (DOL) starter? a) It reduces the starting torque b) It provides better motor protection during operation c) It allows for faster motor acceleration d) It is simpler to wire and operate

Answer 35

a) It reduces the starting torque

Question 36

Which of the following is a potential disadvantage of a Star-Delta starter? a) It causes excessive torque during starting b) It is only suitable for small motors c) It produces a dip in voltage during the transition from Star to Delta d) It uses more energy during normal operation

Answer 36

c) It produces a dip in voltage during the transition from Star to Delta

Question 37

The Star-Delta starter is typically used for motors rated at: a) Low power (below 5 kW) b) High power (above 15 kW) c) Medium power (above 5 kW but below 15 kW) d) Very low power (below 2 kW)

Answer 37

c) Medium power (above 5 kW but below 15 kW)

Question 38

Which of the following is NOT a component of a typical Star-Delta starter circuit? a) Timer relay b) Contactor c) Overload relay d) Variable Frequency Drive (VFD)

Answer 38

d) Variable Frequency Drive (VFD)

Question 39

In a Star-Delta starter, the motor windings receive full line voltage in which configuration? a) Star configuration b) Delta configuration c) Both Star and Delta configurations d) Neither Star nor Delta configurations

Answer 39

b) Delta configuration

Question 40

Which of the following best describes the transition process from Star to Delta in a Star-Delta starter? a) The transition occurs immediately upon starting the motor b) The transition occurs after a time delay or when a certain motor speed is reached c) The motor remains in Star configuration during its entire operation d) The transition occurs when the motor overheats

Answer 40

b) The transition occurs after a time delay or when a certain motor speed is reached

Question 41

Which of the following is a common type of water level controller used in households? a) Float switch b) Pressure regulator c) Flow meter d) Solenoid valve

Answer 41

a) Float switch

Question 42

Which of the following is a primary function of an industrial automation system? a) Data entry b) Material transport c) Process control d) Product design

Answer 42

c) Process control

Question 43

Which of these sensors is typically used to detect the position of an object? a) Temperature sensor b) Proximity sensor c) Pressure sensor d) Humidity sensor

Answer 43

b) Proximity sensor

Question 44

Which type of motor is most commonly used in industrial automation? a) Stepper motor b) DC motor c) Servo motor d) Induction motor

Answer 44

d) Induction motor

Question 45

What is the advantage of using a relay in a control circuit? A) Relays require high power to operate B) Relays provide isolation between control and power circuits C) Relays are used to regulate voltage D) Relays increase the speed of electrical signals

Answer 45

B) Relays provide isolation between control and power circuits

Question 46

Which type of relay is commonly used in time-delay operations? A) Latching relay B) Solid-state relay C) Thermal relay D) Timer relay

Answer 46

D) Timer relay

Question 47

In an industrial control system, which of the following can be controlled using a relay? A) Temperature only B) Motor operation C) Pressure sensors D) Fluid levels

Answer 47

B) Motor operation

Question 48

What is the main difference between a solid-state relay (SSR) and an electromechanical relay? A) SSR has moving parts B) SSR operates with no moving parts C) Electromechanical relays are faster than SSRs D) SSRs are prone to mechanical wear

Answer 48

B) SSR operates with no moving parts

Question 49

Which of the following is a typical application of an industrial relay? A) Amplifying weak electrical signals B) Reducing power consumption C) Controlling high-power loads using low-power signals D) Converting DC to AC

Answer 49

C) Controlling high-power loads using low-power signals

Question 50

In an automatic reverse-forward motor control circuit, what is the primary purpose of using two contactors? A) To provide power to the motor continuously B) To control the direction of the motor's rotation C) To prevent the motor from overheating D) To reduce the speed of the motor

Answer 50

B) To control the direction of the motor's rotation

Question 51

Which of the following components is essential to prevent short-circuiting in a reverse-forward motor control circuit? A) Overload relay B) Limit switch C) Interlocking mechanism D) Timer relay

Answer 51

C) Interlocking mechanism

Question 52

What happens when both the forward and reverse contactors in a motor control circuit are energized at the same time? A) The motor will run in reverse B) The motor will run in forward C) The motor will short circuit D) The motor will stop immediately

Answer 52

C) The motor will short circuit

Question 53

In an automatic reverse-forward motor control system, what is the role of the overload relay? A) To reverse the direction of the motor B) To disconnect power in case of excessive current C) To control the speed of the motor D) To automatically switch between forward and reverse

Answer 53

B) To disconnect power in case of excessive current

Question 54

Which of the following devices is commonly used to start and stop an industrial motor? A) Contactor B) Thermistor C) Diode D) Transformer

Answer 54

A) Contactor

Question 55

What is the function of a Variable Frequency Drive (VFD) in motor control? A) To change the direction of motor rotation B) To protect the motor from overload C) To control the motor speed by varying the frequency of the power supply D) To convert AC to DC power

Answer 55

C) To control the motor speed by varying the frequency of the power supply

Question 56

Which motor control device is designed to disconnect the motor from the power source in case of a short circuit or overload? A) Circuit breaker B) Soft starter C) Contactor D) Push-button switch

Answer 56

A) Circuit breaker

Question 57

What is the primary role of a soft starter in motor control? A) To reduce mechanical stress during motor start-up B) To reverse the direction of the motor C) To prevent the motor from overheating D) To maintain a constant motor speed

Answer 57

A) To reduce mechanical stress during motor start-up

Question 58

Which of the following sensors is commonly used with temperature controllers? A) LVDT B) Thermocouple C) Accelerometer D) Proximity sensor

Answer 58

B) Thermocouple

Question 59

What is the main advantage of a PID temperature controller over an ON/OFF controller? A) PID controllers are less expensive B) PID controllers provide more precise and stable temperature control C) PID controllers can operate without sensors D) PID controllers respond more slowly to temperature changes

Answer 59

B) PID controllers provide more precise and stable temperature control

Question 60

Which of the following is NOT a type of temperature controller? A) ON/OFF Controller B) Digital Controller C) Time-Delay Controller D) Proportional Controller

Answer 60

C) Time-Delay Controller

Question 61

Which component in a temperature control system directly adjusts the heating or cooling elements? A) Relay B) Thermistor C) Actuator D) Controller output

Answer 61

D) Controller output

Question 62

A thermistor used in temperature controllers is a device that: A) Converts temperature changes into voltage B) Changes its resistance based on temperature C) Generates heat based on electrical input D) Detects humidity levels

Answer 62

B) Changes its resistance based on temperature

Question 63

In an industrial temperature control system, a hysteresis setting is used to: A) Measure the difference between maximum and minimum temperatures B) Prevent short cycling by adding a delay between switching on and off C) Reduce the temperature gradually over time D) Increase the speed of temperature changes

Answer 63

B) Prevent short cycling by adding a delay between switching on and off

Question 64

A 24VDC power supply is not working. With your multimeter you verify no DC voltage. On the 120VAC input you measure 120V between hot and ground, and 72V between hot and neutral. What is the most likely cause of this? A) Lost the ground B) Lost the hot C) Lost the neutral D) Lost the fuse

Answer 64

C) Lost the neutral

Question 65

A temperature measuring device that produces a voltage as the temperature changes is a/an: A) RTD B) Thermistor C) Thermometer D) Thermocouple

Answer 65

D) Thermocouple