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EWRB THEORY EXAM PREP QUESTIONS WITH CORRECT ANSWERS 2025
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EWRB THEORY EXAM PREP QUESTIONS WITH CORRECT ANSWERS 2025
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HOSMERITEWRB 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.
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