EWRB Theory Exam Prep Complete with Latest Questions and A+
Graded Verified Answers
What is the minimum value of the permitted test result for the insulation resistance test of a
three-phase, 400V, mains cable?
1MΩ
When carrying out testing on a low voltage electrical installation, which document details the
tests and checks required to be carried out?
AS/NZS 3000
What is the minimum or maximum test result value you would consider acceptable for an Earth
Continuity test?
1Ω or less
State TWO types of electrical protection provided by a RCBO.
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?
√3 & Power Factor
What type of single-phase motor can be reversed by reversing the connections to the run
winding?
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?
ANY ONE:
- Universal Motor
- Series Motor
,State ONE reason why the metal frame of a Class 1 electrical appliance is earthed.
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.
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?
Insulation Resistance Test
State the main reason why interlocks are used in a star/delta starter.
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
0.748
pf = P/V×I×√3
Define the term CUT OFF TIME as it refers to HRC fuses.
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).
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.
718.75A
MEN switchboards have characteristics that are NOT FOUND on a distribution board. Name
TWO of those characteristics.
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?
They have a constant rotating magnetic field.
State TWO reasons for using reduced voltage starting for a three-phase induction motor.
ANY TWO:
- Reduced starting current.
- Reducing voltage fluctuation/surges.
- Limiting mechanical shock.
What is the permitted protective earthing conductor test result for a test between the earth pin
of an appliance supply plug and the earth led accessible metal?
1Ω Max
State the reason why the secondary voltage of a transformer is less at full-load than at no-load.
When current is flowing there is an internal volt drop due to the impedance of the windings.
What is the minimum value of the permitted test result for the insulation resistance test of a
three-phase, 400V, mains cable?
1MΩ
What is the maximum value of the permitted test result for an earth leakage test of a 230V,
Class 1, plug-in appliance?
5mA
State TWO types of fault that a MCB provides protection for.
, - Short-Circuit
- Overload
What type of fault does a RCD provide protection for?
Earth Faults
State the full name for a PRCD.
Portable Residual Current Device.
State the full name for a RCBO.
Residual Circuit Breaker with Overcurrent protection.
State the full name for a SRCD.
Socket Residual Circuit Breaker.
State ONE practical method used to reduce iron losses in the construction of a transformer.
ANY ONE:
- Laminate the iron core.
- Use special types of alloy for the core.
State TWO methods of reducing the stroboscopic effect of a fluorescent fittings installed across
three-phases.
ANY TWO:
- Connect fittings on different phases.
- In double-tube fittings, connect a capacitor in series with one ballast or install lead/lag fittings.
- Intersperse incandescent lighting with the fluorescent lighting.
Explain the term SENSITIVITY as it applies to a RCD.
Sensitivity is the current imbalance (earth leakage) required to trip the RCD.
In a Star connected electrical system, state the angle between line voltage and phase voltage.
30º
In New Zealand, what type of RCD is required to be voltage dependent?
Portable Residual Current Device (PRCD)
State the maximum residual current rating for a RCD installed in a patient treatment are.
10mA
Graded Verified Answers
What is the minimum value of the permitted test result for the insulation resistance test of a
three-phase, 400V, mains cable?
1MΩ
When carrying out testing on a low voltage electrical installation, which document details the
tests and checks required to be carried out?
AS/NZS 3000
What is the minimum or maximum test result value you would consider acceptable for an Earth
Continuity test?
1Ω or less
State TWO types of electrical protection provided by a RCBO.
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?
√3 & Power Factor
What type of single-phase motor can be reversed by reversing the connections to the run
winding?
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?
ANY ONE:
- Universal Motor
- Series Motor
,State ONE reason why the metal frame of a Class 1 electrical appliance is earthed.
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.
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?
Insulation Resistance Test
State the main reason why interlocks are used in a star/delta starter.
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
0.748
pf = P/V×I×√3
Define the term CUT OFF TIME as it refers to HRC fuses.
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).
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.
718.75A
MEN switchboards have characteristics that are NOT FOUND on a distribution board. Name
TWO of those characteristics.
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?
They have a constant rotating magnetic field.
State TWO reasons for using reduced voltage starting for a three-phase induction motor.
ANY TWO:
- Reduced starting current.
- Reducing voltage fluctuation/surges.
- Limiting mechanical shock.
What is the permitted protective earthing conductor test result for a test between the earth pin
of an appliance supply plug and the earth led accessible metal?
1Ω Max
State the reason why the secondary voltage of a transformer is less at full-load than at no-load.
When current is flowing there is an internal volt drop due to the impedance of the windings.
What is the minimum value of the permitted test result for the insulation resistance test of a
three-phase, 400V, mains cable?
1MΩ
What is the maximum value of the permitted test result for an earth leakage test of a 230V,
Class 1, plug-in appliance?
5mA
State TWO types of fault that a MCB provides protection for.
, - Short-Circuit
- Overload
What type of fault does a RCD provide protection for?
Earth Faults
State the full name for a PRCD.
Portable Residual Current Device.
State the full name for a RCBO.
Residual Circuit Breaker with Overcurrent protection.
State the full name for a SRCD.
Socket Residual Circuit Breaker.
State ONE practical method used to reduce iron losses in the construction of a transformer.
ANY ONE:
- Laminate the iron core.
- Use special types of alloy for the core.
State TWO methods of reducing the stroboscopic effect of a fluorescent fittings installed across
three-phases.
ANY TWO:
- Connect fittings on different phases.
- In double-tube fittings, connect a capacitor in series with one ballast or install lead/lag fittings.
- Intersperse incandescent lighting with the fluorescent lighting.
Explain the term SENSITIVITY as it applies to a RCD.
Sensitivity is the current imbalance (earth leakage) required to trip the RCD.
In a Star connected electrical system, state the angle between line voltage and phase voltage.
30º
In New Zealand, what type of RCD is required to be voltage dependent?
Portable Residual Current Device (PRCD)
State the maximum residual current rating for a RCD installed in a patient treatment are.
10mA
