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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. What should the duty rating of a grounding resistor be?
A device used to store electrical energy.
Full-load - three-phase voltage.
A.C.
Continuous.

2. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Shunted and taped
Second-degree burn.
480 volts.
15 feet off the ground.

3. What steps up or steps down AC voltage?
Tied together
Inductance.
Transformer
800 volts.

4. What value of voltage will be measured from phase-to-phase - in a wye-connected secondary - if 2 -300 volts is measured from phase-to-ground?
Nearly constant.
5:1
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.

5. The property of an electric circuit that opposes any change in current is called...
Inductance.
Capacitance.
Short-circuited after power has been removed.
The current will read zero.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
Full-load - three-phase voltage.
Carotid pulse - which is located in the neck next to the Adam's apple.
25 feet.
Lower current and higher voltage

7. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
They must be installed at least 7 feet above the ground.
1 amp.
Disconnect the frame-grounding conductor.

8. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Potential transformer.
12 to 15 times a minute.
Nearly constant.

9. The size of a transformer is measured in...
Lower current and higher voltage.
Draw less current.
800 volts.
Kilovolt ampere (KVA).

10. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Alternating current.
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformer

11. A solenoid coil is...
An electromagnet.
150 turns.
60 cycles per second (60 Hertz).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

12. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Lower current and higher voltage.
The chest should rise or inflate.
Four times less than that of the secondary.
Second-degree burn.

13. When not connected to a load - the secondary leads of a current transformer should be...
Short-circuited after power has been removed.
It provides good speed control.
Shunted and taped
A step-up transformer.

14. 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?
Derive a neutral for grounding purposes.
277 volts.
600 volts.
At least two phases

15. Where should grounding resistors be located?
Potential transformer.
Transformer
At the source transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

16. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
480 volts.
60 Hertz
They should be made by the same manufacturer.
An electromagnet.

17. A control power transformer...
Lower current and higher voltage
277 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
25 feet.

18. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
5:1.
Isolation transformer.
277 volts.
Short-circuited after power has been removed.

19. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Squirrel-cage rotor.
Current that changes constantly in magnitude and periodically in direction.

20. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The current will read zero.
Larger than that found in the primary winding.
An electrical shock hazard may exist.

21. Alternating current may be defined as...
2000 watts
Draw less current.
Lower current and higher voltage
Current that changes constantly in magnitude and periodically in direction.

22. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
Two speeds
Lower current and higher voltage
The current will read zero.

23. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Squirrel-cage induction motor.
Disconnect the frame-grounding conductor.
The capacitors should be discharged.

24. The primary function of a power transformer is to provide...
Four times less than that of the secondary.
Circuit Breaker.
Full-load - three-phase voltage.
100 volts.

25. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Transformer
Derive a neutral for grounding purposes.
Nearly constant.

26. What type motor is a wound-rotor induction motor?
A.C.
480 volts.
12 to 15 times a minute.
Carotid pulse - which is located in the neck next to the Adam's apple.

27. High voltage is used to transmit power over long distances...
The current will read zero.
1 amp.
Derive a neutral for grounding purposes.
Because less current flowing at high voltage causes less line loss per kilowatt.

28. Find the turns ratio of a single-phase transformer with the following values: Primary power of 5KW - secondary current of 100 amps - and primary voltage of 250 volts.
Draw less current.
Squirrel-cage induction motor.
Four times less than that of the secondary.
5:1

29. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Nearly constant.
Capacitance.
An electrical shock hazard may exist.

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

31. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
The current will read zero.
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Derive a neutral for grounding purposes.

32. Compared to the secondary of a loaded - step-down transformer - the primary has...
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
277 volts.

33. A burn causing a blister is classified as a...
Second-degree burn.
Current that changes constantly in magnitude and periodically in direction.
100 volts.
1 amp.

34. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
480 volts.
150 turns.
No.6 AWG.
Zero amps.

35. Current in an AC circuit may be measured by...
They should be made by the same manufacturer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Clamp-on ammeter.
Kilovolt ampere (KVA).

36. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Alternating current.
Transformers.
Grounded phase and ground fault devices were not operating.
200 volts AC.

37. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Tied together
15 feet off the ground.
Cut around clothing that has adhered to the burned area.

38. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Check to make sure that the victim is not still in contact with the electricity.
1 amp.
200 volts AC.
2000 watts

39. The combined capacitance of two capacitors in parallel is...
5:1
Hyperventilation.
Potential transformer.
The sum of the two capacitors.

40. Two 10-hp induction motors are operating on 460 volts AC. One motor is connected by single- phase; the other is connected in three-phase. The three-phase will...
Transformers.
Draw less current.
An electrical shock hazard may exist.
The current will read zero.

41. 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...
Continuous.
Draw less current.
Circuit Breaker.
Current changing constantly in magnitude and periodically in direction.

42. How do you change the direction of a 3-phase AC motor?
Inductance.
Reverse any two-phase leads.
Current that changes constantly in magnitude and periodically in direction.
A grounding resistor.

43. 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...
100 volts.
A step-up transformer.
An electrical shock hazard may exist.
An electromagnet.

44. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
They should be made by the same manufacturer.
A grounding resistor.
Inductance.
The chest should rise or inflate.

45. A transformer with 1 -500 turns in the primary winding has a primary voltage of 2 -400 volts and a secondary voltage of 120 volts. How many turns are in the secondary winding?
15 feet off the ground.
75 turns.
Reverse any two-phase leads.
Second-degree burn.

46. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Current changing constantly in magnitude and periodically in direction.
75 turns.
Lower current and higher voltage

47. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Full-load - three-phase voltage.
Electro-magnetism for their operation.
1 amp.

48. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
25 feet.
Nearly constant.
The chest should rise or inflate.

49. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Circuit Breaker.
Four times less than that of the secondary.
Grounded phase and ground fault devices were not operating.

50. Not true about AC power?
It provides good speed control.
A device used to store electrical energy.
Inductance.
277 volts.