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EWRB (Electrical Engineering) THEORY LATEST UPDATED.
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EWRB (Electrical Engineering) THEORY LATEST UPDATED.
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EWRB (Electrical Engineering) THEORY LATESTUPDATED.
State one reason why an earth fault-loop impedance test is carried out on
the socket outlet furthest from the main switchboard in a low voltage
electrical installation?
✔✔Any ONE of:
● To confirm that the electrical protection for the final subcircuit will
operate within the required time.
● To confirm that the electrical protection all other final subcircuits
supplied from the main switchboard will operate with the required time.
Define the term cut off characteristic as it applies to an HRC fuse.
✔✔This is the value of fault current that cuts off (operates) the fuse that
is less than the prospective short-circuit current.
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 sub
circuit supplying the induction motor.
✔✔To provide short-circuit fault protection to both the final sub circuit
and the motor
,State one hazard that could occur when disposing of low-pressure or
high-pressure sodium-vapour lamps
✔✔Any ONE of:
● Fire risk (sodium + moisture produces hydrogen)
● Risk of chemical burns (sodium + water produces sodium hydroxide
(caustic soda))
When the load on a transformer changes from no-load to full-load a
voltage drop occurs at the secondary terminals.
Is this voltage drop normal?
State a reason to support your answer
✔✔Yes
Because of the current flow through the impedance of the windings
This is a block diagram of a three-phase circuit to a three-phase star-
connected hot water cylinder in a factory.
Switchboard - lockable isolator - contactor - HWC
HRC fuses protect the final sub circuit to the three-phase HWC.
, The existing hot water cylinder is to be removed . The new cylinder will
be installed once building alterations have been completed
Describe how to isolate the existing hot water cylinder
✔✔The description must show:
- opening the isolator or removing the fuses
- doing a voltage test at the load side of the isolator (or the supply side of
the contactor).
- Using the prove-test-prove method to confirm isolation has occurred
- locking the isolator open
-attaching a danger tag to the isolator
Building alterations have been completed. A new correctly-rated flexible
cable has been connected to the new hot water cylinder.
State TWO instrument tests that must be carried out on the new flexible
cable and hot water cylinder to ensure that they are safe to connect to the
electricity supply.
✔✔Earth continuity test
Insulation resistance test
State ONE reason why rectified three-phase a.c. Is easier to smooth with
filters, than rectified single-phase a.c.
✔✔Ensure the circuit is still isolated by using the prove-test-prove
method.
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