Electrician Theory Test Flashcards
State TWO requirements for good illumination.
Any TWO of:
● Provides clear vision without eye strain
● Sufficient light intensity
● Minimum glare
● Uniform light intensity throughout the illuminated area
● Suitable colour rendering
A new 230V electrical installation incorporates permanently-connected electrical equipment with MIMS elements.
State the permitted test result for an insulation resistance test for the electrical installation with all the permanently-connected electrical equipment disconnected.
1MΩ
A new 230V electrical installation incorporates permanently-connected electrical equipment with MIMS elements.
State the permitted test result for an insulation resistance test for the electrical installation with all the permanently-connected electrical equipment connected.
0.01MΩ
A three-phase induction motor normally runs on full-load. State ONE reason why this motor should not be run lightly loaded when it normally runs on full load.
Any ONE of:
● The power factor of the motor will be poor
● The motor will be less efficient.
● Running costs rise
A three-phase induction motor has been operating normally on full-load. The motor starts to over-heat even though it is drawing the normal full load current.
State ONE reason why this situation would occur.
Any ONE of:
● The motor ventilation is restricted in some manner.
● The cooling fan has become detached from the motor shaft
A clip-on ammeter is being used to test the 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?
Clamped around the protective earthing conductor
State the maximum test result that would allow the appliance to be returned to service.
5 mA
Describe the basic operation of a gas discharge lamp.
Light is produced by an electric discharge by passing current through a gas or vapour in the discharge tube
State two requirements for good illumination
Any TWO of:
- Provides clear vision without eye strain
- Sufficient light intensity
- Minimum glare
- Uniform light intensity throughout the illuminated area
- Suitable colour rendering
Explain what is meant by the term inverse time-current characteristic in relation to protective devices?
● As the current through the protective device increases.
● The time taken to operate decreases
State TWO components that are typically used to smooth the d.c. output of a rectifier.
Any TWO of:
● Capacitors
● Inductors
● Resistors
The output circuit of an autotransformer must be insulated for the highest input or output voltage of the autotransformer.
State ONE reason for this requirement.
An auto transformer can fail in such a way so the primary voltage appears across the secondary.
A Class I, plug-in electric heater is designed for use on 230V/240V supply. An ohmmeter reads 24 Ω when measured at the plug.
Use calculations to show the supply voltage being used if the power dissipated is 2204W.
V = √(P x R) = √(2204 X 24) = 230V
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?
The internal circuitry of the electrical equipment would be live when the isolating switch is in the OFF position.
State ONE formula used to determine the power factor of a three-phase inductive load.
pf = P / (√3 x VL x IL)
