EWRB Exam: Questions And Proper Solutions
In New Zealand, the standard distribution system has the neutral conductor
connected to the earth at the main switchboard on all low voltage
installations. What name is given to this type of system? Right Ans -
Multiple Earthed Neutral or MEN system.
State the test voltage used for carrying out an insulation resistance test on
three-phase, 400V, electrical equipment incorporating MIMS elements.
Right Ans - 500v dc
State one reason why the resistance of the protective earthing conductor of a
flexible cord for a Class I electrical appliance is set at a maximum of 1 Ω
Right Ans - Under fault conditions, it prevents the touch voltages rising to
dangerous levels.
To ensure sufficient fault current flows to operate the protective device
State one factor that determines the voltage drop in a 400V, final subcircuit
TPS cable. Right Ans - Type of conductor material
Cross-sectional area
Load
Length of cable
An isolator for 230V electrical equipment has been replaced. During the work
the phase (active) and neutral were accidentally transposed at the supply side
of the isolating switch. What potential danger would this transposition create?
Right Ans - The internal circuitry of the electrical equipment would be live
when the isolating switch is in the OFF position
A voltage test for isolation is being carried out on a three-phase, 400V oven
that may or may not be live. State the main safety issue that would occur if the
only testing done was between each phase. Right Ans - One phase could
still be alive.
List two types of earth electrode that may be used to connect an MEN system
to the mass of earth. Right Ans - Earth rod
Buried electrode
Metallic reinforcing
, Earth mat
State what is meant by the term current rating as it applies to an HRC fuse?
Right Ans - This is the maximum current that the fuse is designed to carry
continuously
State one reason why an RCD tester is used to test a PRCD. Right Ans - To
verify that the PRCD operates within specified residual current limits.
To verify that the PRCD operates within specified time limits
A three-phase induction motor is controlled by a star/delta starter that
incorporates thermal overloads.
State one reason why HRC fuses are installed at the origin of the final
subcircuit supplying the induction motor Right Ans - To provide short-
circuit fault protection to both the final subcircuit and the motor.
Define the term isolation as it relates to three-phase equipment. Right Ans -
Means the equipment has been deliberately disconnected from the electricity
supply
And precautions have been taken to prevent reconnection of the supply to the
equipment
Describe how the prove-test-prove method of testing is carried out. Right
Ans - The test instrument is checked to be operating correctly on a known live
source
The equipment is tested to confirm (or otherwise) that it is isolated
The test instrument is again checked on a known live source to ensure it still
operates correctly
Give a brief description of circumstances when a Danger Tag is used Right
Ans - Where there is a possibility of personal danger through the supply being
restored.
Give a brief description of circumstances when an Out-of-Service Tag is used.
Right Ans - Where equipment is faulty or damaged and using that equipment
would cause damage or injury
State two precautions to be taken when attaching a danger tag to an isolating
switch Right Ans - Make sure the correct isolating switch is tagged.
In New Zealand, the standard distribution system has the neutral conductor
connected to the earth at the main switchboard on all low voltage
installations. What name is given to this type of system? Right Ans -
Multiple Earthed Neutral or MEN system.
State the test voltage used for carrying out an insulation resistance test on
three-phase, 400V, electrical equipment incorporating MIMS elements.
Right Ans - 500v dc
State one reason why the resistance of the protective earthing conductor of a
flexible cord for a Class I electrical appliance is set at a maximum of 1 Ω
Right Ans - Under fault conditions, it prevents the touch voltages rising to
dangerous levels.
To ensure sufficient fault current flows to operate the protective device
State one factor that determines the voltage drop in a 400V, final subcircuit
TPS cable. Right Ans - Type of conductor material
Cross-sectional area
Load
Length of cable
An isolator for 230V electrical equipment has been replaced. During the work
the phase (active) and neutral were accidentally transposed at the supply side
of the isolating switch. What potential danger would this transposition create?
Right Ans - The internal circuitry of the electrical equipment would be live
when the isolating switch is in the OFF position
A voltage test for isolation is being carried out on a three-phase, 400V oven
that may or may not be live. State the main safety issue that would occur if the
only testing done was between each phase. Right Ans - One phase could
still be alive.
List two types of earth electrode that may be used to connect an MEN system
to the mass of earth. Right Ans - Earth rod
Buried electrode
Metallic reinforcing
, Earth mat
State what is meant by the term current rating as it applies to an HRC fuse?
Right Ans - This is the maximum current that the fuse is designed to carry
continuously
State one reason why an RCD tester is used to test a PRCD. Right Ans - To
verify that the PRCD operates within specified residual current limits.
To verify that the PRCD operates within specified time limits
A three-phase induction motor is controlled by a star/delta starter that
incorporates thermal overloads.
State one reason why HRC fuses are installed at the origin of the final
subcircuit supplying the induction motor Right Ans - To provide short-
circuit fault protection to both the final subcircuit and the motor.
Define the term isolation as it relates to three-phase equipment. Right Ans -
Means the equipment has been deliberately disconnected from the electricity
supply
And precautions have been taken to prevent reconnection of the supply to the
equipment
Describe how the prove-test-prove method of testing is carried out. Right
Ans - The test instrument is checked to be operating correctly on a known live
source
The equipment is tested to confirm (or otherwise) that it is isolated
The test instrument is again checked on a known live source to ensure it still
operates correctly
Give a brief description of circumstances when a Danger Tag is used Right
Ans - Where there is a possibility of personal danger through the supply being
restored.
Give a brief description of circumstances when an Out-of-Service Tag is used.
Right Ans - Where equipment is faulty or damaged and using that equipment
would cause damage or injury
State two precautions to be taken when attaching a danger tag to an isolating
switch Right Ans - Make sure the correct isolating switch is tagged.
