EWRB Theory Exam Prep questions with complete solution updated 2024/25
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Course
EWRB
Institution
EWRB
These topics encapsulate the fundamental aspects of the EWRB Theory Exam, making them important for candidates.
Knowledge of types of MCB trips, including thermal and magnetic tripping mechanisms, is essential for effective circuit protection 2.
Understanding the minimum permitted test results fo...
EWRB Theory Exam Prep questions with complete solution
updated 2024/25
What is the minimum value of the permitted test result for the insulation
resistance test of a three-phase, 400V, mains cable? - correct answer ✔ 1MΩ
When carrying out testing on a low voltage electrical installation, which document
details the tests and checks required to be carried out? - correct answer ✔
AS/NZS 3000
What is the minimum or maximum test result value you would consider
acceptable for an Earth Continuity test? - correct answer ✔ 1Ω or less
State TWO types of electrical protection provided by a RCBO. - correct 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? - correct answer ✔ √3 &
Power Factor
What type of single-phase motor can be reversed by reversing the connections to
the run winding? - correct 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? - correct answer ✔ ANY ONE:
- Universal Motor
- Series Motor
State ONE reason why the metal frame of a Class 1 electrical appliance is earthed.
- correct 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. - correct answer ✔ ANY TWO:
- Voltage Applied
- Shock Current Level
- Contact Duration
- Skin Dryness
- Current Path
, EWRB Theory Exam Prep questions with complete solution
updated 2024/25
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? -
correct answer ✔ Insulation Resistance Test
State the main reason why interlocks are used in a star/delta starter. - correct
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 - correct answer ✔ 0.748
pf = P/V×I×√3
Define the term CUT OFF TIME as it refers to HRC fuses. - correct 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). - correct 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. - correct answer ✔ 718.75A
MEN switchboards have characteristics that are NOT FOUND on a distribution
board. Name TWO of those characteristics. - correct 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? - correct answer ✔ They have a constant rotating
magnetic field.
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