HOSMERIT
EWRB THEORY EXAM PREP QUESTIONS WITH
CORRECT 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
State TWO reasons for using reduced voltage starting for a three-phase induction motor. -
ANSWER- ANY TWO:
- Reduced starting current.
- Reducing voltage fluctuation/surges.
- Limiting mechanical shock.
State TWO methods of PHASE-SPLITTING used to provide the starting torque in a single-phase
induction motor. - ANSWER- 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. - ANSWER- ANY TWO:
- Snubber circuit
- MOV (surge diverter)
- Free-wheeling diode
- RC circuit
- Optocoupler/Relay
- UPS
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.
Explain why it is necessary to have a protective earthing conductor in a final subcircuit protected
by a RCD. - ANSWER- In order for the RCD to operate, an earth leakage path must exist.
EWRB THEORY EXAM PREP QUESTIONS WITH
CORRECT 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
State TWO reasons for using reduced voltage starting for a three-phase induction motor. -
ANSWER- ANY TWO:
- Reduced starting current.
- Reducing voltage fluctuation/surges.
- Limiting mechanical shock.
State TWO methods of PHASE-SPLITTING used to provide the starting torque in a single-phase
induction motor. - ANSWER- 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. - ANSWER- ANY TWO:
- Snubber circuit
- MOV (surge diverter)
- Free-wheeling diode
- RC circuit
- Optocoupler/Relay
- UPS
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.
Explain why it is necessary to have a protective earthing conductor in a final subcircuit protected
by a RCD. - ANSWER- In order for the RCD to operate, an earth leakage path must exist.
