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Electrical Theory WITH ANSWERS GRADED A+
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Electrical Theory WITH ANSWERS GRADED A+
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10/5/24, 12:09 PMEUNICE
Electrical Theory WITH 100% SURE ANSWERS
State the permissible test result for an 1 Mega Ohm
insulation resistance test for the electrical
installation with ALL the permanently-
connected electrical equipment
DISCONNECTED
State the permissible test result for an 0.01 Mega Ohms
insulation resistance test for the electrical
installation with ALL the permanently-
connected electrical equipment
CONNECTED
A three-phase induction motor normally - The power factor of the motor will be poor
runs on full-load. State ONE reason why - The motor will be less efficient
this motor should not be run LIGHTLY - running costs rise
LOADED when it runs on full load.
A three-phase induction motor has been - The motor ventilation is restricted in some manner
OPERATING NORMALLY ON FULL-LOAD. - The cooling fan has become detached from the motor shaft
The motor starts to over-heat even though
it is drawing the normal full load current.
State ONE reason why this situation would
occur
A clip-on ammeter is being used to test the Clamped around the protective earthing conductor and 5mA
integrity of the insulation of a repaired
Class I electrical appliance, while the
appliance is live. Where on the appliance
would the clip-on ammeter be used? Also
state the maximum test result that would
allow the appliance to return to service.
Explain what is meant by the term INVERSE as current through the protective device increases, the time taken to operate
TIME-CURRENT CHARACTERISTIC in decreases
relation to protective devices
1/8
, 10/5/24, 12:09 PM
- Capacitors
State TWO components that are typically
- Inductors
used to smooth the d.c output of a rectifier
- Resistors
The output circuit of an autotransformer An auto transformer can fail in such a way so the primary voltage appears across the
MUST BE insulated for the highest input or secondary
output voltage of the autotransformer.
State ONE reason for this requirement
An isolator for 230V electrical equipment The internal circuitry of the electrical equipment would be live when the isolating
has been replaced. During the work the switch is in the OFF position.
phase (active) and neutral were
accidentally transposed at the supply side
of the isolating switch.
What potential danger would this
transposition create?
What to the initials BJT mean when applied A bi-polar junction transistor
to semiconductors
State the function of a transducer A device that changes energy from one form to another
Any TWO of:
● Provides clear vision without eye strain
● Sufficient light intensity
State TWO requirements for good
illumination
● Minimum glare
● Uniform light intensity throughout the illuminated area
● Suitable colour rendering
XC Capacitive Reactance (ohms)
Explain why REWIREABLE FUSES are There is no certainty that the fuse will operate within 4 hours at 1.5x it's rated current
classed COARSE EXCESS CURRENT
protection
Explain why gG type HRC fuses and MCBs The HRC fuse or MCB will operate with certainty within 4 hours at 1.5x its rated
are classed as close current protection current
The total time taken for a HRC fuse to 1. The pre-arcing time is the time taken for a fault current large enough to operate the
operate is defined as the total operating (or fuse. Or the time between the fuse elements beginning to melt and the initiation of
clearance) time. The total clearance time the arc
comprises the pre-arcing time and the
arcing time. 2. The arcing time is the time between the initiation of the arc and the extinguishing of
the arc
1. Define the term pre-arcing time
2. Define the term arcing time
Describe how correct discrimination is Only the protective devices closest to the fault operates
achieved between protective devices in an
electrical installation
2/8
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