2010more

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mike9111
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159037
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2010more
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2012-06-16 23:03:48
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  1. which tests must becarried out with the socket outlet and circuit live?
    Any ONE of: Earth loop impedance test RCD test Polarity test
  2. An electrician has wired a remote stop-start station to an existing DOL230V starter circuit that controls a three-phase motor. The DOL starterwas working normally before the work commenced.After the work had been completed the motor could be turned on but couldnot be turned off using either of the stop buttons.What is the cause of this fault?
    The stop buttons have been wired inparallel
  3. An RCD test has been carried out on a portable residual current device.The device passed the residual current trip test.What additional check must be carried out on the portable residual currentdevice to ensure it is electrically safe?
    It has to be tested to ensure that it isvoltage-dependent (that is, it will notautomatically reset if supply is restored.)
  4. The phase and neutral on the supply side of a single phase RCD have beentransposed.Would the RCD operate if it detected an earth leakage fault on the circuit itprotects? State a reason to support your answer.
    Yes (½ mark)The RCD detects the imbalance regardless of (½ mark)Class I equipment loadSensingcoil/toroidTripping DeviceE N LTestbutton
  5. State the full names for the following terms:(3 marks)PRCD ________________________________________________________________________________________________________RCBO ________________________________________________________________________________________________________SRCD ________________________________________________________________________________________________________
    PRCD Portable Residual Current Device. (1 mark)RCBO Residual Circuit Breaker withOvercurrent protection(1 mark)SRCD Socket Residual Current Device
  6. An earth loop impedance test result of 0.32F has been recorded on a 230Vfinal subcircuit supplying socket outlets in a low voltage electricalinstallation.Calculate the fault current that will flow if a short circuit occurs on the finalsubcircuit.
    IF = VZ(½ mark)= 2300.32(½ mark)= 718.75A
  7. A MEN, low voltage domestic installation is required to have a mainearthing conductor.(i) To which parts of the electrical installation are the ends of the mainearthing conductor connected?
    (i)  The earth bar The earth electrode
  8. What is required to be attached at each end of the main earthingconductor?
    Tags warning against disconnection
  9. State the maximum permitted rated residual current of an RCD installedfor:(i) Personal protection in a domestic installation.(1 mark)________________________________________________________(ii) Personal protection in a medical-electrical installation.(1 mark)________________________________________________________(iii) The protection of property.(1 mark)________________________________________________________
    (i) 30 milliamps. (1 mark)(ii) 10 milliamps (1 mark)(iii) Between 100 milliamps and 300milliamps.
  10. A person is using a Class I electrical appliance supplied from an RCDprotected final subcircuit. An earth leakage fault occurs and earth leakagecurrent flows through the person’s body.Why doesn’t the person receive a severe electric shock when the earthleakage current flows through their body?
    Because the RCD trips in milliseconds
  11. A Residual Current Circuit Breaker (RCCB) is installed in a single phasecircuit.Explain why the RCCB does not operate when there is a short circuitbetween active (phase) and neutral in the single phase circuit?
    Any ONE of: (2 marks) The short circuit does not produce animbalance between the phase anneutral currents in the RCCB The RCCB does not incorporate anoverload function.
  12. In New Zealand, what type of RCD is required to be voltagedependent.
    (i) Portable Residual Current Device
  13. The low voltage installation is protected on the distribution supply systemby a 60A rewireable pole fuse.State the main reason why a phase and neutral transposition on the mainswill not operate (“blow”) the pole fuse
    Any ONE of: (2 marks) The fault current is too low to blow thefuse. Because the impedance of the faultloop is too high.
  14. What does the term IP mean?
    International protection Ingress protection
  15. What type of protection is indicated by the first digit? IP
    Protection against the ingress ofsolid objects

    Protection against the ingress ofdust 
  16. What type of protection is indicated by the second digit?
    Protection against the ingress of water
  17. What would be the typical connection for a three-phase, 400V, 20kWmotor?
    Any ONE of: Delta connection DOL starter Star/delta starter
  18. The motor is to be started direct on-line and protected by a thermaloverload unit and HRC fuses. The thermal overload unit is incorporated inthe DOL starter and protects the motor from overloads.Briefly explain the term overload as it relates to the thermal overload.
     A current larger that the current settingof the thermal overload.(1 mark) That is sustained long enough tooperate the overload
  19. An insulation resistance test is carried out with a test voltage of 500V d.c.(i) Briefly explain why a voltage of 500V is applied.
    To stress the insulation at levelsabove the nominal operating (orpeak) voltage
  20. Briefly explain why the voltage is a d.c. voltage.
    Any ONE of:. To ensure capacitive orinductive reactance does notinfluence the test result.. A constant maximum voltageis a more stringent test thanthe momentary peaks of ana.c. waveform.
  21. The MEN connection of the installation is located at the inside switchboard.This is the place where you have carried out the insulation resistance test.The installation has a range and a water heater installed, both theseappliances contain MIMS elements.(i) You carried out the insulation resistance test and the result for theentire installation was 0.2 MF.State the most likely reason why the test result is lower than thepermitted value of 1 MF.
    Either the range or the waterheater (or both) have insulationresistance much lower than 1 M;

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