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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
If you are not ready to take this test, you can study here.
Match each statement with the correct term.
Don't refresh. All questions and answers are randomly picked and ordered every time you load a test.

This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.

1. Current in an AC circuit may be measured by...
200 volts AC.
60 cycles per second (60 Hertz).
Clamp-on ammeter.
Larger than that found in the primary winding.

2. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage.
An electrical shock hazard may exist.
5:1.

3. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Zero amps.
They must be installed at least 7 feet above the ground.
100 turns.
277 volts.

4. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The current will read zero.
2000 watts
Cut around clothing that has adhered to the burned area.

5. The primary function of a power transformer is to provide...
Continuous.
Full-load - three-phase voltage.
Isolation transformer.
The current will read zero.

6. Where should grounding resistors be located?
75 turns.
At the source transformer.
Check to make sure that the victim is not still in contact with the electricity.
Grounded phase and ground fault devices were not operating.

7. AC voltage is raised or lowered by means of...
Transformers.
Grounded phase and ground fault devices were not operating.
The motor rotation is reversed.
Short-circuited after power has been removed.

8. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
100 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse any two-phase leads.

9. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Clamp-on ammeter.
5:1
Transformers.
Short-circuited after power has been removed.

10. If any two-phase wires are reversed on a three-phase motor - the motor will...
75 turns.
100 volts.
Reverse its rotation.
Allow for metering voltage and Current.

11. The standard frequency of alternating current used at a mine is...
Short-circuited after power has been removed.
Kilovolt ampere (KVA).
Full-load - three-phase voltage.
60 Hertz

12. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Short-circuited after power has been removed.
X.
25 feet.
They must be installed at least 7 feet above the ground.

13. The standard frequency of power supplied by the power company is...
A device used to store electrical energy.
Because less current flowing at high voltage causes less line loss per kilowatt.
60 cycles per second (60 Hertz).
Squirrel-cage induction motor.

14. Under fault conditions - the grounding resistor in a high voltage circuit limits the voltage drop in the grounding circuit external to the resistor to not more than...
Allow for metering voltage and Current.
Clamp-on ammeter.
No.6 AWG.
100 volts.

15. Three-phase AC underground cables must be provided with overcurrent protection using a...
60 Hertz
Circuit Breaker.
Draw less current.
Tied together

16. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
100 turns.
Lower current and higher voltage.
No.6 AWG.
H terminals.

17. A solenoid coil is...
Check to make sure that the victim is not still in contact with the electricity.
An electromagnet.
25 feet.
Short-circuited after power has been removed.

18. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Transformers.
Reverse any two-phase leads.
The capacitors should be discharged.
Inductance.

19. The purpose of a zig-zag transformer is to...
Inductance.
Derive a neutral for grounding purposes.
Cut around clothing that has adhered to the burned area.
Squirrel-cage rotor.

20. The speed of an alternating current - squirrel-cage induction motor is...
Current that changes constantly in magnitude and periodically in direction.
Nearly constant.
Lower current and higher voltage.
The current will read zero.

21. What is the first step to be followed in aiding a victim of electrical shock?
12 to 15 times a minute.
Because less current flowing at high voltage causes less line loss per kilowatt.
Check to make sure that the victim is not still in contact with the electricity.
They must be installed at least 7 feet above the ground.

22. The main function of CT's and PT's on a main substation is to...
100 volts.
Shunted and taped
Allow for metering voltage and Current.
7 -630 volts.

23. Not a symptom of electrical shock?.
H terminals.
Short-circuited after power has been removed.
A grounding resistor.
Hyperventilation.

24. What is the danger when working around capacitors?
Reverse its rotation.
Tied together
An electrical shock hazard may exist.
A grounding resistor.

25. The most reliable method to use to determine whether or not the heart has stopped is by checking the...

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26. A transformer has 1 -600 turns in the primary and 400 turns in the secondary. The primary voltage is 2 -400 volts. What is the secondary voltage?
100 volts.
No.6 AWG.
600 volts.
Check to make sure that the victim is not still in contact with the electricity.

27. Alternating current may be defined as...
60 cycles per second (60 Hertz).
A.C.
Current that changes constantly in magnitude and periodically in direction.
Provides single-phase power to smaller loads such as lights - heaters - etc.

28. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
Zero amps.
200 volts AC.
They should be made by the same manufacturer.
Reverse any two-phase leads.

29. A burn causing a blister is classified as a...
Second-degree burn.
Grounded phase and ground fault devices were not operating.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Continuous.

30. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Current that changes constantly in magnitude and periodically in direction.
25 feet.
They must be installed at least 7 feet above the ground.
Derive a neutral for grounding purposes.

31. 460 volts AC is required to operate two motors - one connected in single-phase and the other connected in three-phase. The three-phase motor will...
Draw less current.
They should be made by the same manufacturer.
Reverse its rotation.
At the source transformer.

32. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Four times less than that of the secondary.
Continuous.
1 amp.
Larger than that found in the primary winding.

33. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
5:1.
Disconnect the frame-grounding conductor.
Potential transformer.

34. Current that changes periodically in direction is...
2000 watts
Nearly constant.
25 feet.
Alternating current.

35. The property of an electric circuit that opposes any change in current is called...
At the source transformer.
A grounding resistor.
12 to 15 times a minute.
Inductance.

36. High voltage is used to transmit power over long distances...
Continuous.
Because less current flowing at high voltage causes less line loss per kilowatt.
A device used to store electrical energy.
600 volts.

37. A transformer has a primary voltage of 2 -400 volts and a secondary reading of 120 volts. If there are 1 -500 turns on the primary - how many turns are on the secondary?
Squirrel-cage rotor.
Isolation transformer.
15 feet off the ground.
75 turns.

38. How do you change the direction of a 3-phase AC motor?
No.6 AWG.
Reverse any two-phase leads.
Reverse its rotation.
Zero amps.

39. At what rate should mouth-to-mouth resuscitation be applied?
A step-up transformer.
12 to 15 times a minute.
Potential transformer.
Derive a neutral for grounding purposes.

40. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Full-load - three-phase voltage.
Kilovolt ampere (KVA).
They should be made by the same manufacturer.
Short-circuited after power has been removed.

41. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Continuous.
Hyperventilation.
480 volts.
The chest should rise or inflate.

42. The primary leads of a single-phase transformer should be connected to the...
Transformers.
H terminals.
Potential transformer.
At the source transformer.

43. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
277 volts.
Alternating current.
Draw less current.

44. Operating coils - motors - transformers - relays and solenoids depend upon...
100 volts.
Kilovolt ampere (KVA).
Electro-magnetism for their operation.
12 to 15 times a minute.

45. A transformer has 2000 turns in the primary and 500 turns in the secondary. The primary voltage is 3 -200 volts. What is the secondary voltage?
150 turns.
800 volts.
2000 watts
5:1.

46. What should the duty rating of a grounding resistor be?
Continuous.
Alternating current.
12 to 15 times a minute.
Shunted and taped

47. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Lower current and higher voltage.
They must be installed at least 7 feet above the ground.
The chest should rise or inflate.

48. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Nearly constant.
Transformers.
Alternating current.
Two speeds

49. Which of the following does a squirrel cage induction motor have?
Stator windings.
X.
150 turns.
The sum of the two capacitors.

50. A control power transformer...
Isolation transformer.
A grounding resistor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.