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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. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Isolation transformer.
75 turns.
5:1.

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

3. Three-phase AC underground cables must be provided with overcurrent protection using a...
60 Hertz
Hyperventilation.
Circuit Breaker.
Four times less than that of the secondary.

4. High voltage is used to transmit power over long distances...
Continuous.
The chest should rise or inflate.
Check to make sure that the victim is not still in contact with the electricity.
Because less current flowing at high voltage causes less line loss per kilowatt.

5. Which of the following does a squirrel cage induction motor have?
Electro-magnetism for their operation.
Stator windings.
The sum of the two capacitors.
Inductance.

6. The transformer used only to measure voltage is a...
Grounded phase and ground fault devices were not operating.
15 feet off the ground.
Potential transformer.
A.C.

7. A burn causing a blister is classified as a...
An electromagnet.
Second-degree burn.
7 -630 volts.
A grounding resistor.

8. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
The current will read zero.
Reverse any two-phase leads.
Inductance.

9. Current in an AC circuit may be measured by...
An electromagnet.
Clamp-on ammeter.
Reverse its rotation.
Cut around clothing that has adhered to the burned area.

10. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Electro-magnetism for their operation.
Inductance.
Squirrel-cage rotor.

11. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Transformer
Short-circuited after power has been removed.
Check to make sure that the victim is not still in contact with the electricity.
277 volts.

12. 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.
75 turns.
200 volts AC.
Stator windings.

13. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
X.
2000 watts
7 -630 volts.
Continuous.

14. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
An electrical shock hazard may exist.
3 -979 Volts.
The chest should rise or inflate.

15. Alternating current may be defined as...
Full-load - three-phase voltage.
Draw less current.
Current that changes constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).

16. If any two-phase wires are reversed on a three-phase motor - the motor will...
Squirrel-cage induction motor.
Reverse its rotation.
At least two phases
60 cycles per second (60 Hertz).

17. What type of 3-phase AC motor is used most often around a mine?
A device used to store electrical energy.
X.
Squirrel-cage induction motor.
200 volts AC.

18. The standard frequency of alternating current used at a mine is...
Transformers.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds
60 Hertz

19. 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?
5:1.
200 volts AC.
75 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

20. Current that changes periodically in direction is...
The current will read zero.
At the source transformer.
Lower current and higher voltage
Alternating current.

21. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
277 volts.
They must be installed at least 7 feet above the ground.
Hyperventilation.
15 feet off the ground.

22. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Two speeds
2000 watts
Continuous.

23. Operating coils - motors - transformers - relays and solenoids depend upon...
Grounded phase and ground fault devices were not operating.
Four times less than that of the secondary.
Electro-magnetism for their operation.
Allow for metering voltage and Current.

24. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Four times less than that of the secondary.
A grounding resistor.
Transformer
480 volts.

25. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Provides single-phase power to smaller loads such as lights - heaters - etc.
12 to 15 times a minute.
Grounded phase and ground fault devices were not operating.

26. What should the duty rating of a grounding resistor be?
Draw less current.
Continuous.
277 volts.
Check to make sure that the victim is not still in contact with the electricity.

27. The speed of an alternating current - squirrel-cage induction motor is...
Derive a neutral for grounding purposes.
60 Hertz
Nearly constant.
Transformer

28. A transformer has a primary voltage of 2 -800 volts and a secondary reading of 140 volts. If there are 2000 turns on the primary - how many turns are on the secondary?
Disconnect the frame-grounding conductor.
H terminals.
100 turns.
Clamp-on ammeter.

29. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Continuous.
15 feet off the ground.
Squirrel-cage induction motor.

30. 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?
277 volts.
X.
800 volts.
Lower current and higher voltage

31. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Alternating current.
The chest should rise or inflate.
They must be installed at least 7 feet above the ground.

32. The purpose of a zig-zag transformer is to...
Four times less than that of the secondary.
12 to 15 times a minute.
Derive a neutral for grounding purposes.
5:1

33. What is the danger when working around capacitors?
At least two phases
An electrical shock hazard may exist.
100 turns.
Hyperventilation.

34. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Four times less than that of the secondary.
No.6 AWG.
Isolation transformer.
Grounded phase and ground fault devices were not operating.

35. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Squirrel-cage induction motor.
1 amp.
Two speeds
Draw less current.

36. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Reverse any two-phase leads.
The chest should rise or inflate.
X.
200 volts AC.

37. 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?
Lower current and higher voltage
200 volts AC.
Hyperventilation.
15 feet off the ground.

38. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
200 volts AC.
25 feet.
Inductance.
Reverse its rotation.

39. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Disconnect the frame-grounding conductor.
Inductance.
Current that changes constantly in magnitude and periodically in direction.
No.6 AWG.

40. A control power transformer...
A step-up transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
At least two phases
X.

41. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Draw less current.
Nearly constant.
Disconnect the frame-grounding conductor.
No.6 AWG.

42. The property of an electrical circuit that opposes any change in voltage is called...
The current will read zero.
Second-degree burn.
Capacitance.
They should be made by the same manufacturer.

43. 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.
60 cycles per second (60 Hertz).
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.

44. A transformer with a 1:1 ratio is usually a (an)...
Tied together
No.6 AWG.
15 feet off the ground.
Isolation transformer.

45. 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?
12 to 15 times a minute.
3 -979 Volts.
Potential transformer.
480 volts.

46. The primary leads of a single-phase transformer should be connected to the...
2000 watts
150 turns.
Nearly constant.
H terminals.

47. 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?
X.
H terminals.
75 turns.
Two speeds

48. When not connected to a load - the secondary leads of a current transformer should be...
1 amp.
800 volts.
75 turns.
Shunted and taped

49. What steps up or steps down AC voltage?
Reverse its rotation.
Full-load - three-phase voltage.
Transformer
Second-degree burn.

50. A 3-phase - 2 speed - constant torque motor is running at fast speed. The motor windings are connected wye for fast speed. Motor leads T4 - T5 and T6 are connected to the line leads. Motor leads T1 - T2 and T3 should be...
200 volts AC.
Short-circuited after power has been removed.
Tied together
Second-degree burn.