EWRB THEORY UPDATED 2026 EXAM SCRIPT
QUESTIONS AND SOLUTIONS RATED A+
✔✔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
✔✔State TWO reasons why a RUN CAPACITOR would be fitted to a single-phase,
split-phase induction motor. - ✔✔ANY TWO:
- Quieter running.
- Better running torque.
- Less current draw.
- Increased efficiency.
✔✔Name TWO components that are typically used to smooth the DC output of a
rectifier. - ✔✔ANY TWO:
- Capacitors
- Inductors
- Resistors
- Transistor
- Zener Diode
- Voltage Regulator
✔✔Explain what is meant by the term, INVERSE TIME-CURRENT CHARACTERISTIC
in relation to a protective device. - ✔✔As the current through the protective device
increases, the time taken to operate decreases.
(The larger the current flowing through a protective device, the quicker it will operate).
✔✔State TWO factors that determine the prospective short-circuit current in an
electrical installation. - ✔✔ANY TWO:
- Supply voltage.
,- The impedance if the earth fault loop.
- Capacity (kA) of the supply source.
✔✔State EIGHT components of a MEN system that are found in a MEN low voltage
installation. - ✔✔- Main earth bar
- Main earthing conductor
- Earth electrode
- MEN link (connection)
- Main neutral bar
- Main neutral conductor
- Protective earthing conductors
- Equipotential bonding conductors
✔✔State the main function of the main earthing conductor and the earth electrode in a
low voltage, MEN installation. - ✔✔ANY ONE:
- To connect the parts of an installation required to be earthed, to the mass of earth.
- To keep the neutral potential to 0V.
- To keep the phase potential to 230V.
✔✔Explain why Class || (double-insulated) electrical equipment IS NOT required to be
connected to a protective earthing conductor. - ✔✔There is supplementary insulation
between the basic insulation and any metal that could become live under fault
conditions.
✔✔Explain how the operation of an AC variable speed controller is different to the
operation of an electronic soft starter. - ✔✔- The variable speed controller varies the
FREQUENCY and voltage to vary the speed.
- The electronic soft start varies voltage on starting to limit the starting CURRENT.
✔✔Explain the term RAMP TIME as it relates to an AC variable speed controller. -
✔✔The adjustment that controls the length of time taken for a change in speed to take
place.
✔✔Define extra-low voltage (ELV). - ✔✔<50V AC or 120V DC.
✔✔Define low voltage. - ✔✔50V - 1200V AC or 120V - 1500V DC.
✔✔Define high voltage. - ✔✔>1000V AC or 1500V DC.
✔✔Explain coarse excess-current protection. - ✔✔When a protection device does NOT
interrupt a fault current within 4 hours when a fault current is 1.5 times that of the rated
current of the protection device.
, ✔✔Explain close excess-current protection. - ✔✔When a protection device DOES
interrupt a fault current within 4 hours when the fault current is 1.5 times the rated
current of the protection device.
✔✔What is another term for utilisation category? - ✔✔Fusing factor.
✔✔Apart from cost, state TWO technical advantages that HRC fuses have when
compared to MCBs. - ✔✔- Higher kA rating (short circuit protection).
- Faster speed of operation.
✔✔Define the term DISCRIMINATION in relation to electrical protection in an electrical
installation. - ✔✔The protective device CLOSEST to the fault operates before any other
protective device can operate.
✔✔State TWO methods used to cool transformers. - ✔✔ANY TWO:
- Air cooled
- Oil cooled
- Pumped or natural convection
- Forced or natural ventilation
✔✔State the main advantage of a single-phase synchronous motor when compared to
a single-phase induction motor. - ✔✔The synchronous motor rotates at a
constant speed independent of the load.
✔✔Describe how the output voltage of a large power transformer is maintained as the
load changes. - ✔✔A tap-changer is used to maintain the voltage.
✔✔Explain the term BURDEN as it relates to current transformers. - ✔✔It is the total VA
load that can be imposed on a CT.
✔✔State TWO methods of PHASE-SPLITTING used to provide the starting torque in a
single-phase induction motor. - ✔✔ANY TWO:
- A capacitor in series with the auxiliary winding
- Different winding impedances
- A shaded pole
✔✔State TWO devices that can be used to protect semi-conductor components against
the effect of transient voltages. - ✔✔ANY TWO:
- Snubber circuit
- MOV (surge diverter)
- Free-wheeling diode
- RC circuit
- Optocoupler/Relay
- UPS
QUESTIONS AND SOLUTIONS RATED A+
✔✔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
✔✔State TWO reasons why a RUN CAPACITOR would be fitted to a single-phase,
split-phase induction motor. - ✔✔ANY TWO:
- Quieter running.
- Better running torque.
- Less current draw.
- Increased efficiency.
✔✔Name TWO components that are typically used to smooth the DC output of a
rectifier. - ✔✔ANY TWO:
- Capacitors
- Inductors
- Resistors
- Transistor
- Zener Diode
- Voltage Regulator
✔✔Explain what is meant by the term, INVERSE TIME-CURRENT CHARACTERISTIC
in relation to a protective device. - ✔✔As the current through the protective device
increases, the time taken to operate decreases.
(The larger the current flowing through a protective device, the quicker it will operate).
✔✔State TWO factors that determine the prospective short-circuit current in an
electrical installation. - ✔✔ANY TWO:
- Supply voltage.
,- The impedance if the earth fault loop.
- Capacity (kA) of the supply source.
✔✔State EIGHT components of a MEN system that are found in a MEN low voltage
installation. - ✔✔- Main earth bar
- Main earthing conductor
- Earth electrode
- MEN link (connection)
- Main neutral bar
- Main neutral conductor
- Protective earthing conductors
- Equipotential bonding conductors
✔✔State the main function of the main earthing conductor and the earth electrode in a
low voltage, MEN installation. - ✔✔ANY ONE:
- To connect the parts of an installation required to be earthed, to the mass of earth.
- To keep the neutral potential to 0V.
- To keep the phase potential to 230V.
✔✔Explain why Class || (double-insulated) electrical equipment IS NOT required to be
connected to a protective earthing conductor. - ✔✔There is supplementary insulation
between the basic insulation and any metal that could become live under fault
conditions.
✔✔Explain how the operation of an AC variable speed controller is different to the
operation of an electronic soft starter. - ✔✔- The variable speed controller varies the
FREQUENCY and voltage to vary the speed.
- The electronic soft start varies voltage on starting to limit the starting CURRENT.
✔✔Explain the term RAMP TIME as it relates to an AC variable speed controller. -
✔✔The adjustment that controls the length of time taken for a change in speed to take
place.
✔✔Define extra-low voltage (ELV). - ✔✔<50V AC or 120V DC.
✔✔Define low voltage. - ✔✔50V - 1200V AC or 120V - 1500V DC.
✔✔Define high voltage. - ✔✔>1000V AC or 1500V DC.
✔✔Explain coarse excess-current protection. - ✔✔When a protection device does NOT
interrupt a fault current within 4 hours when a fault current is 1.5 times that of the rated
current of the protection device.
, ✔✔Explain close excess-current protection. - ✔✔When a protection device DOES
interrupt a fault current within 4 hours when the fault current is 1.5 times the rated
current of the protection device.
✔✔What is another term for utilisation category? - ✔✔Fusing factor.
✔✔Apart from cost, state TWO technical advantages that HRC fuses have when
compared to MCBs. - ✔✔- Higher kA rating (short circuit protection).
- Faster speed of operation.
✔✔Define the term DISCRIMINATION in relation to electrical protection in an electrical
installation. - ✔✔The protective device CLOSEST to the fault operates before any other
protective device can operate.
✔✔State TWO methods used to cool transformers. - ✔✔ANY TWO:
- Air cooled
- Oil cooled
- Pumped or natural convection
- Forced or natural ventilation
✔✔State the main advantage of a single-phase synchronous motor when compared to
a single-phase induction motor. - ✔✔The synchronous motor rotates at a
constant speed independent of the load.
✔✔Describe how the output voltage of a large power transformer is maintained as the
load changes. - ✔✔A tap-changer is used to maintain the voltage.
✔✔Explain the term BURDEN as it relates to current transformers. - ✔✔It is the total VA
load that can be imposed on a CT.
✔✔State TWO methods of PHASE-SPLITTING used to provide the starting torque in a
single-phase induction motor. - ✔✔ANY TWO:
- A capacitor in series with the auxiliary winding
- Different winding impedances
- A shaded pole
✔✔State TWO devices that can be used to protect semi-conductor components against
the effect of transient voltages. - ✔✔ANY TWO:
- Snubber circuit
- MOV (surge diverter)
- Free-wheeling diode
- RC circuit
- Optocoupler/Relay
- UPS
