Ewrb Theory Exam Prep
Questions With Correct Detailed
Answers 2025.
What is the minimum value of the permitted test result for the insulation resistance test
of a three-phase, 400V, mains cable? - ANSWER- 1MΩ
When carrying out testing on a low voltage electrical installation, which document
details the tests and checks required to be carried out? - ANSWER- AS/NZS 3000
What is the minimum or maximum test result value you would consider acceptable for
an Earth Continuity test? - ANSWER- 1Ω or less
State TWO types of electrical protection provided by a RCBO. - ANSWER- ANY TWO:
- Earth Leakage
- Overload
- Short Circuit
If the voltage and current are known, what TWO other factors are required to calculate
the power consumed by a three-phase motor? - ANSWER- √3 & Power Factor
What type of single-phase motor can be reversed by reversing the connections to the
run winding? - ANSWER- ANY ONE:
- Split-Phase Motor
- Capacitor Start Motor
- Cap-Start, Cap-Run Motor
What type of single-phase motor can be reversed by reversing the connections to the
armature brushes? - ANSWER- ANY ONE:
- Universal Motor
- Series Motor
State ONE reason why the metal frame of a Class 1 electrical appliance is earthed. -
ANSWER- ANY ONE:
- To ensure the operation of a protective device under fault conditions.
- To keep the frame of the appliance at earth potential under fault conditions.
State TWO factors that determine the severity of electric shock upon the human body. -
ANSWER- ANY TWO:
- Voltage Applied
- Shock Current Level
- Contact Duration
, - Skin Dryness
- Current Path
You have carried out a test on a low voltage final subcircuit in an electrical installation,
the result value was 20MΩ. What type of test has been carried out? - ANSWER-
Insulation Resistance Test
State the main reason why interlocks are used in a star/delta starter. - ANSWER- To
prevent the star and delta contractors closing simultaneously - and causing a short
circuit.
Calculate the power factor of a small three-phase printing factory with mainly motor
loading. Metering instruments have recorded the following:
Power = 30000W
Voltage = 406V
Current = 57A per phase - ANSWER- 0.748
pf = P/V×I×√3
Define the term CUT OFF TIME as it refers to HRC fuses. - ANSWER- ANY ONE:
- Pre-arcing Time: Time taken to melt the fuse elements.
- Arcing Time: The time taken between the initiation of the arc, and the arc
extinguishing.
- Cut Off Current: The fault current that will cause the fuse to blow.
- Total Clearing Time: The time it takes to interrupt the flow of current and extinguish the
flame.
State the purpose of the slip-rings on a wound rotor induction motor (or slip-ring motor).
- ANSWER- To connect the external resistance to the wound motor.
Calculate the fault current if a short circuit occurs on a 230V final subcircuit with an
earth loop impedance test result of 0.32Ω. - ANSWER- 718.75A
MEN switchboards have characteristics that are NOT FOUND on a distribution board.
Name TWO of those characteristics. - ANSWER- ANY TWO:
A MEN switchboard:
- Has a MEN link between the neutral and earth busbars.
- Has a connection to earth via an earthing lead to an earth electrode.
- Is electrically closest to the point of supply.
- Can supply to another MEN switchboard.
Why do three-phase induction motors run smoother and quieter than single-phase
induction motors? - ANSWER- They have a constant rotating magnetic field.
State TWO reasons for using reduced voltage starting for a three-phase induction
motor. - ANSWER- ANY TWO:
- Reduced starting current.
Questions With Correct Detailed
Answers 2025.
What is the minimum value of the permitted test result for the insulation resistance test
of a three-phase, 400V, mains cable? - ANSWER- 1MΩ
When carrying out testing on a low voltage electrical installation, which document
details the tests and checks required to be carried out? - ANSWER- AS/NZS 3000
What is the minimum or maximum test result value you would consider acceptable for
an Earth Continuity test? - ANSWER- 1Ω or less
State TWO types of electrical protection provided by a RCBO. - ANSWER- ANY TWO:
- Earth Leakage
- Overload
- Short Circuit
If the voltage and current are known, what TWO other factors are required to calculate
the power consumed by a three-phase motor? - ANSWER- √3 & Power Factor
What type of single-phase motor can be reversed by reversing the connections to the
run winding? - ANSWER- ANY ONE:
- Split-Phase Motor
- Capacitor Start Motor
- Cap-Start, Cap-Run Motor
What type of single-phase motor can be reversed by reversing the connections to the
armature brushes? - ANSWER- ANY ONE:
- Universal Motor
- Series Motor
State ONE reason why the metal frame of a Class 1 electrical appliance is earthed. -
ANSWER- ANY ONE:
- To ensure the operation of a protective device under fault conditions.
- To keep the frame of the appliance at earth potential under fault conditions.
State TWO factors that determine the severity of electric shock upon the human body. -
ANSWER- ANY TWO:
- Voltage Applied
- Shock Current Level
- Contact Duration
, - Skin Dryness
- Current Path
You have carried out a test on a low voltage final subcircuit in an electrical installation,
the result value was 20MΩ. What type of test has been carried out? - ANSWER-
Insulation Resistance Test
State the main reason why interlocks are used in a star/delta starter. - ANSWER- To
prevent the star and delta contractors closing simultaneously - and causing a short
circuit.
Calculate the power factor of a small three-phase printing factory with mainly motor
loading. Metering instruments have recorded the following:
Power = 30000W
Voltage = 406V
Current = 57A per phase - ANSWER- 0.748
pf = P/V×I×√3
Define the term CUT OFF TIME as it refers to HRC fuses. - ANSWER- ANY ONE:
- Pre-arcing Time: Time taken to melt the fuse elements.
- Arcing Time: The time taken between the initiation of the arc, and the arc
extinguishing.
- Cut Off Current: The fault current that will cause the fuse to blow.
- Total Clearing Time: The time it takes to interrupt the flow of current and extinguish the
flame.
State the purpose of the slip-rings on a wound rotor induction motor (or slip-ring motor).
- ANSWER- To connect the external resistance to the wound motor.
Calculate the fault current if a short circuit occurs on a 230V final subcircuit with an
earth loop impedance test result of 0.32Ω. - ANSWER- 718.75A
MEN switchboards have characteristics that are NOT FOUND on a distribution board.
Name TWO of those characteristics. - ANSWER- ANY TWO:
A MEN switchboard:
- Has a MEN link between the neutral and earth busbars.
- Has a connection to earth via an earthing lead to an earth electrode.
- Is electrically closest to the point of supply.
- Can supply to another MEN switchboard.
Why do three-phase induction motors run smoother and quieter than single-phase
induction motors? - ANSWER- They have a constant rotating magnetic field.
State TWO reasons for using reduced voltage starting for a three-phase induction
motor. - ANSWER- ANY TWO:
- Reduced starting current.
