CWEA ELECTRICAL/INSTRUMENTATION TECHNOLOGIST
290 ACTUAL QUESTIONS AND CORRECT ANSWERS WITH
RATIONALE ALREADY GRADED A+
1. Which of the following is the primary function of a current transformer (CT) in
electrical systems?
a) To increase voltage
b) To measure high currents safely
c) To store electrical energy
d) To protect against overvoltage
Answer: b) To measure high currents safely
Rationale: A current transformer reduces high currents to a lower, measurable
value, allowing safe measurement and monitoring by instruments and protective
devices .
2. What is the total resistance of two 100-ohm resistors connected in parallel?
a) 200 ohms
b) 100 ohms
c) 50 ohms
d) 25 ohms
Answer: c) 50 ohms
Rationale: For two equal resistors in parallel, total resistance RT = R ÷ 2 = 100 ÷
2 = 50 ohms .
3. In a three-phase system, what is the voltage between any two line conductors
called?
a) Phase voltage
b) Line voltage
c) Neutral voltage
d) Ground voltage
Answer: b) Line voltage
Rationale: In a three-phase system, the voltage between any two line conductors
is called line voltage. In a wye system, line voltage is √3 times phase voltage; in a
delta system, line and phase voltage are equal.
,4. An electrical motor that is protected from overload by a thermal overload heater
will:
a) Trip a circuit breaker
b) Open a control circuit contact
c) Blow a fuse
d) Short circuit the motor
Answer: b) Open a control circuit contact
Rationale: Overload heaters are designed to open a control circuit contact when
excessive current is detected, which de-energizes the motor starter coil and stops
the motor .
5. What is the voltage from phase to ground in a 480V transformer?
a) 120 volts
b) 208 volts
c) 240 volts
d) 277 volts
Answer: d) 277 volts
Rationale: In a 480V three-phase wye-connected system, the phase-to-ground
voltage is 277V (480V ÷ √3 = 277V) .
6. What is the most common type of AC motor used at a treatment plant?
a) Wound rotor induction motor
b) Synchronous motor
c) Squirrel cage induction motor
d) Universal motor
Answer: c) Squirrel cage induction motor
Rationale: The squirrel cage induction motor is the most common AC motor in
industrial applications due to its simple construction, low cost, and reliability .
7. What should insulation resistance be when tested with a megger?
a) 0.5 megohm per 1,000 volts, minimum 0.5 megohm
b) 1 megohm per 1,000 volts, minimum 1 megohm
c) 2 megohm per 1,000 volts, minimum 2 megohm
d) 5 megohm per 1,000 volts, minimum 5 megohm
Answer: b) 1 megohm per 1,000 volts, minimum 1 megohm
Rationale: The standard rule of thumb for insulation resistance testing is 1
megohm for each 1,000 volts of operating voltage, with a minimum acceptable
value of 1 megohm .
8. Which of the following is NOT a required element to start a fire?
, a) Heat
b) Oxygen
c) Nitrogen
d) Fuel
Answer: c) Nitrogen
Rationale: The three elements needed to start a fire are heat, oxygen, and fuel
(the "fire triangle"). Nitrogen is not required for combustion .
9. A transformer has a primary voltage of 120V and a secondary voltage of 12V
with 20 amps on the secondary. What are the amps on the primary?
a) 1 amp
b) 2 amps
c) 3 amps
d) 4 amps
Answer: b) 2 amps
Rationale: Power remains constant (ignoring losses). Secondary power = 12V ×
20A = 240 watts. Primary current = 240W ÷ 120V = 2 amps .
10. In a 240V-120V Delta system, the "high leg" (stinger leg) voltage to neutral is:
a) 120 volts
b) 208 volts
c) 240 volts
d) 277 volts
Answer: b) 208 volts
Rationale: In a 240V delta system with a center-tapped transformer, the voltage
from the high leg to neutral is 208V .
11. What happens when a motor loses one phase out of three?
a) Motor continues normal operation
b) Motor stops immediately
c) Single phasing will cause the motor to trip the overload heaters
d) Motor speed increases
Answer: c) Single phasing will cause the motor to trip the overload heaters
Rationale: Single phasing occurs when one phase is lost, causing the motor to
draw excessive current on the remaining phases and trip the overload heaters .
12. Which of the following describes "Current"?
a) Electrical pressure
b) Resistance to flow
c) The flow of electrons
, d) Total work done
Answer: c) The flow of electrons
Rationale: Current is the flow of electrical charge (electrons) through a
conductor, measured in Amperes. Voltage is electrical pressure, and resistance
opposes current flow .
13. What is the current in a 120V circuit with a resistance of 30 ohms?
a) 1 amp
b) 2 amps
c) 3 amps
d) 4 amps
Answer: d) 4 amps
Rationale: Using Ohm's Law: I = E ÷ R = 120V ÷ 30Ω = 4 amps .
14. In a parallel circuit, the voltage across each branch is:
a) The same as the source voltage
b) Divided equally among branches
c) Different in each branch
d) Zero in some branches
Answer: a) The same as the source voltage
Rationale: In a parallel circuit, the voltage is the same across each branch
because all branches are connected directly to the power source .
15. An inductor is best described as:
a) A device that stores energy in an electric field
b) A coil of wire that opposes any change in current
c) A component that increases voltage
d) A device that measures current
Answer: b) A coil of wire that opposes any change in current
Rationale: An inductor is a coil of wire that opposes changes in current flow,
storing energy in a magnetic field .
16. Which of the following reduces high voltages and currents to safe values for
measurements?
a) Auto transformer
b) Megohmmeter
c) Instrument transformer
d) Variable transformer
Answer: c) Instrument transformer
290 ACTUAL QUESTIONS AND CORRECT ANSWERS WITH
RATIONALE ALREADY GRADED A+
1. Which of the following is the primary function of a current transformer (CT) in
electrical systems?
a) To increase voltage
b) To measure high currents safely
c) To store electrical energy
d) To protect against overvoltage
Answer: b) To measure high currents safely
Rationale: A current transformer reduces high currents to a lower, measurable
value, allowing safe measurement and monitoring by instruments and protective
devices .
2. What is the total resistance of two 100-ohm resistors connected in parallel?
a) 200 ohms
b) 100 ohms
c) 50 ohms
d) 25 ohms
Answer: c) 50 ohms
Rationale: For two equal resistors in parallel, total resistance RT = R ÷ 2 = 100 ÷
2 = 50 ohms .
3. In a three-phase system, what is the voltage between any two line conductors
called?
a) Phase voltage
b) Line voltage
c) Neutral voltage
d) Ground voltage
Answer: b) Line voltage
Rationale: In a three-phase system, the voltage between any two line conductors
is called line voltage. In a wye system, line voltage is √3 times phase voltage; in a
delta system, line and phase voltage are equal.
,4. An electrical motor that is protected from overload by a thermal overload heater
will:
a) Trip a circuit breaker
b) Open a control circuit contact
c) Blow a fuse
d) Short circuit the motor
Answer: b) Open a control circuit contact
Rationale: Overload heaters are designed to open a control circuit contact when
excessive current is detected, which de-energizes the motor starter coil and stops
the motor .
5. What is the voltage from phase to ground in a 480V transformer?
a) 120 volts
b) 208 volts
c) 240 volts
d) 277 volts
Answer: d) 277 volts
Rationale: In a 480V three-phase wye-connected system, the phase-to-ground
voltage is 277V (480V ÷ √3 = 277V) .
6. What is the most common type of AC motor used at a treatment plant?
a) Wound rotor induction motor
b) Synchronous motor
c) Squirrel cage induction motor
d) Universal motor
Answer: c) Squirrel cage induction motor
Rationale: The squirrel cage induction motor is the most common AC motor in
industrial applications due to its simple construction, low cost, and reliability .
7. What should insulation resistance be when tested with a megger?
a) 0.5 megohm per 1,000 volts, minimum 0.5 megohm
b) 1 megohm per 1,000 volts, minimum 1 megohm
c) 2 megohm per 1,000 volts, minimum 2 megohm
d) 5 megohm per 1,000 volts, minimum 5 megohm
Answer: b) 1 megohm per 1,000 volts, minimum 1 megohm
Rationale: The standard rule of thumb for insulation resistance testing is 1
megohm for each 1,000 volts of operating voltage, with a minimum acceptable
value of 1 megohm .
8. Which of the following is NOT a required element to start a fire?
, a) Heat
b) Oxygen
c) Nitrogen
d) Fuel
Answer: c) Nitrogen
Rationale: The three elements needed to start a fire are heat, oxygen, and fuel
(the "fire triangle"). Nitrogen is not required for combustion .
9. A transformer has a primary voltage of 120V and a secondary voltage of 12V
with 20 amps on the secondary. What are the amps on the primary?
a) 1 amp
b) 2 amps
c) 3 amps
d) 4 amps
Answer: b) 2 amps
Rationale: Power remains constant (ignoring losses). Secondary power = 12V ×
20A = 240 watts. Primary current = 240W ÷ 120V = 2 amps .
10. In a 240V-120V Delta system, the "high leg" (stinger leg) voltage to neutral is:
a) 120 volts
b) 208 volts
c) 240 volts
d) 277 volts
Answer: b) 208 volts
Rationale: In a 240V delta system with a center-tapped transformer, the voltage
from the high leg to neutral is 208V .
11. What happens when a motor loses one phase out of three?
a) Motor continues normal operation
b) Motor stops immediately
c) Single phasing will cause the motor to trip the overload heaters
d) Motor speed increases
Answer: c) Single phasing will cause the motor to trip the overload heaters
Rationale: Single phasing occurs when one phase is lost, causing the motor to
draw excessive current on the remaining phases and trip the overload heaters .
12. Which of the following describes "Current"?
a) Electrical pressure
b) Resistance to flow
c) The flow of electrons
, d) Total work done
Answer: c) The flow of electrons
Rationale: Current is the flow of electrical charge (electrons) through a
conductor, measured in Amperes. Voltage is electrical pressure, and resistance
opposes current flow .
13. What is the current in a 120V circuit with a resistance of 30 ohms?
a) 1 amp
b) 2 amps
c) 3 amps
d) 4 amps
Answer: d) 4 amps
Rationale: Using Ohm's Law: I = E ÷ R = 120V ÷ 30Ω = 4 amps .
14. In a parallel circuit, the voltage across each branch is:
a) The same as the source voltage
b) Divided equally among branches
c) Different in each branch
d) Zero in some branches
Answer: a) The same as the source voltage
Rationale: In a parallel circuit, the voltage is the same across each branch
because all branches are connected directly to the power source .
15. An inductor is best described as:
a) A device that stores energy in an electric field
b) A coil of wire that opposes any change in current
c) A component that increases voltage
d) A device that measures current
Answer: b) A coil of wire that opposes any change in current
Rationale: An inductor is a coil of wire that opposes changes in current flow,
storing energy in a magnetic field .
16. Which of the following reduces high voltages and currents to safe values for
measurements?
a) Auto transformer
b) Megohmmeter
c) Instrument transformer
d) Variable transformer
Answer: c) Instrument transformer
