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AC Theory Practice Exam Question and Answers.
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AC Theory Practice Exam Question and Answers.AC Theory Practice Exam Question and Answers.AC Theory Practice Exam Question and Answers.
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AC Theory Practice Exam Question andAnswers.
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? - 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. - ANS 500 V D.Sc.
State the minimum permitted test result for the insulation resistance test on electrical
equipment without MIMS elements - ANS 1MΩ
State the permitted test result for an insulation resistance test for the electrical
installation with all the permanently-connected electrical equipment connected. - ANS
0.01MΩ
State the minimum permitted test result for the insulation resistance test on the
electrical equipment incorporating MIMS elements. - ANS 0.01MΩ
State ONE precaution that could be taken when using an insulation resistance tester,
set on the 500V D.Sc. range, to carry out an insulation resistance test on electrical
equipment containing semi-conductor devices. - ANS Bridge out between phase and
neutral
Why you would take this precaution on electrical equipment containing semi-conductor
devices. - ANS The voltage of the test instrument may damage semi-conductor devices.
AS/NZS 3000 requires that a test voltage of 500V D.Sc. is used for an insulation
resistance test of a low voltage electrical installation. State ONE reason why the voltage
is a D.Sc. voltage. - ANS Any ONE of:
● to ensure capacitive or inductive reactance does not influence the test
Result.
● a constant maximum voltage is a more
Stringent test than the momentary peaks of an arc. waveform.
AS/NZS 3000 requires that a test voltage of 500V D.Sc. is used for an insulation
resistance test of a low voltage electrical installation. Explain why a voltage of 500V is
applied. - ANS to stress the insulation at a voltage
above 325V a.c. (or peak a.c. voltage).
Tests have been carried out on a three-phase 400V, Class I, plug-in electrical appliance
after it has been repaired. The test results are as follows:
,Earth continuity test - out of range
Insulation resistance test - Infinity
What type of fault is indicated by the test results? - ANS Any ONE of:
● A high-resistance joint in the
protective earthing circuit.
● An open-circuit in the protective
earthing conductor.
State THREE actions that need to be taken to ensure the electrical appliance is safe to
return to service. Include acceptable test results in the answer. - ANS ● Repair faulty
protective earthing conductor circuit
● Conduct an earth continuity test To ensure the resistance is 1Ω or less
● Any ONE of:
● Conduct an insulation
resistance test. To ensure the insulation
resistance is 1MΩ or more.
● Conduct an earth leakage
test. To ensure that the leakage does not exceed 5 mA.
Define the term impedance as it applies to an a.c. circuit. - ANS It is the total opposition
in Ω (ohms) to the current flow in an a.c. circuit.
Impedance is comprised of three components. State TWO of those components. - ANS
Any TWO of:
● Resistance (R)
● Inductive reactance (Xl)
● Capacitive reactance (XC)
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. - ANS • Under fault
conditions, it prevents the touch voltages rising to dangerous levels.
• To ensure sufficient fault current flows to operate the protective device
,AS/NZS 3760 details two test methods of verifying that the insulation of a Class I
electrical appliance is in sound condition. For each method state
● The name of the test
● The permitted test result - ANS Insulation resistance test
1 MΩ or 10,000Ω
Earth leakage test
5 mA
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. - ANS
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.
describe the path of the earth fault loop being tested between the earth terminal of the
socket outlet and the phase terminal of the socket outlet. - ANS ● The earth terminal of
the socket outlet
● The final subcircuit earth conductor
● The main earth bar
● The MEN link
● The main neutral bar
● The consumers main neutral
● The distribution neutral
● The star point
● The transformer winding
● The phase conductor
● The main switch
● The switchboard cables
, ● The final subcircuit active conductor
● The phase terminal of the socket outlet
State ONE reason why having a protective earthing conductor resistance of less than 1
Ω in a Class I electrical appliance effectively prevents electric shock hazards under fault
conditions. - ANS Any ONE of:
● Under fault conditions, it prevents the touch voltages rising to dangerous levels.
● To ensure sufficient fault current flows to
State one factor that determines the voltage drop in a 400V, final subcircuit TPS cable. -
ANS Any one of:
• Type of conductor material
• Cross-sectional area
• Load
• Length of cable
A heater is rated at 2 kW when operating at 230V. State what
(i) effect will a voltage drop of 5% have on the resistance of the
heater elements?
(ii) By how much will the power, dissipated by the heater, change if the voltage drops
5%. - ANS (i) No effect.
(ii) Any ONE of:
● The power dissipated drops 10%
● The power dissipated drops 195W
An electrician has installed a three-phase, five-pin, socket outlet and subcircuit wiring in
a bakery. The subcircuit wiring will be connected at the switchboard at a later date.
State the Standard and section of that Standard that specifies the tests and
checks that need to be carried out on the socket outlet and final subcircuit wiring. - ANS
● AS/NZS 3000
● Section 8
State the document that must be completed once all the testing and checking has been
completed. - ANS A certificate of compliance (COC)
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