EWRB THEORY EXAM PREP WITH
COMPLETE SOLUTIONS
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.
State the reason why the secondary voltage of a transformer is less at full-load than at
no-load. - ANSWER-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? - ANSWER-1MΩ
What is the maximum value of the permitted test result for an earth leakage test of a
230V, Class 1, plug-in appliance? - ANSWER-5mA
State TWO types of fault that a MCB provides protection for. - ANSWER-- Short-Circuit
- Overload
What type of fault does a RCD provide protection for? - ANSWER-Earth Faults
State the full name for a PRCD. - ANSWER-Portable Residual Current Device.
State the full name for a RCBO. - ANSWER-Residual Circuit Breaker with Overcurrent
protection.
State the full name for a SRCD. - ANSWER-Socket Residual Circuit Breaker.
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.
COMPLETE SOLUTIONS
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.
State the reason why the secondary voltage of a transformer is less at full-load than at
no-load. - ANSWER-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? - ANSWER-1MΩ
What is the maximum value of the permitted test result for an earth leakage test of a
230V, Class 1, plug-in appliance? - ANSWER-5mA
State TWO types of fault that a MCB provides protection for. - ANSWER-- Short-Circuit
- Overload
What type of fault does a RCD provide protection for? - ANSWER-Earth Faults
State the full name for a PRCD. - ANSWER-Portable Residual Current Device.
State the full name for a RCBO. - ANSWER-Residual Circuit Breaker with Overcurrent
protection.
State the full name for a SRCD. - ANSWER-Socket Residual Circuit Breaker.
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.
