Test your basic knowledge |

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. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
They must be installed at least 7 feet above the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A grounding resistor.

2. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
The capacitors should be discharged.
1 amp.
Disconnect the frame-grounding conductor.
Check to make sure that the victim is not still in contact with the electricity.

3. If any two-phase wires are reversed on a three-phase motor - the motor will...
Inductance.
Transformer
Reverse its rotation.
Grounded phase and ground fault devices were not operating.

4. A solenoid coil is...
480 volts.
An electromagnet.
Draw less current.
100 volts.

5. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Check to make sure that the victim is not still in contact with the electricity.
Squirrel-cage rotor.
A grounding resistor.
The chest should rise or inflate.

6. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A grounding resistor.
A step-up transformer.
75 turns.
X.

7. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Current that changes constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.
100 turns.

8. A wound-rotor induction motor has all the following EXCEPT...
The sum of the two capacitors.
Squirrel-cage rotor.
Draw less current.
Lower current and higher voltage.

9. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The capacitors should be discharged.
Disconnect the frame-grounding conductor.
The motor rotation is reversed.
2000 watts

10. Where should grounding resistors be located?
Current changing constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.
Derive a neutral for grounding purposes.
At the source transformer.

11. 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?
Current that changes constantly in magnitude and periodically in direction.
Draw less current.
No.6 AWG.
100 turns.

12. The purpose of a zig-zag transformer is to...
Shunted and taped
They must be installed at least 7 feet above the ground.
Four times less than that of the secondary.
Derive a neutral for grounding purposes.

13. At what rate should mouth-to-mouth resuscitation be applied?
A.C.
150 turns.
12 to 15 times a minute.
Four times less than that of the secondary.

14. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Inductance.
100 volts.
Clamp-on ammeter.
Grounded phase and ground fault devices were not operating.

15. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Two speeds
15 feet off the ground.
Hyperventilation.

16. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
7 -630 volts.
The current will read zero.
Transformers.

17. The combined capacitance of two capacitors in parallel is...
Reverse any two-phase leads.
The sum of the two capacitors.
Transformers.
Nearly constant.

18. 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?
The motor rotation is reversed.
Disconnect the frame-grounding conductor.
200 volts AC.
Inductance.

19. Find the turns ratio of a single-phase transformer with the following values: Primary power of 10 KW - secondary current of 200 amps - and primary voltage of 250 volts.
60 cycles per second (60 Hertz).
5:1.
Stator windings.
600 volts.

20. The primary leads of a single-phase transformer should be connected to the...
800 volts.
H terminals.
5:1
60 Hertz

21. Alternating current may be defined as...
1 amp.
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.
150 turns.

22. 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.
An electrical shock hazard may exist.
480 volts.
15 feet off the ground.

23. The standard frequency of alternating current used at a mine is...
Two speeds
5:1
60 Hertz
Squirrel-cage induction motor.

24. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
5:1.
Potential transformer.
At the source transformer.

25. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
100 volts.
Capacitance.
60 Hertz
X.

26. 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...
Tied together
Disconnect the frame-grounding conductor.
A device used to store electrical energy.
Derive a neutral for grounding purposes.

27. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Provides single-phase power to smaller loads such as lights - heaters - etc.
Stator windings.
It provides good speed control.
2000 watts

28. A transformer with a 1:1 ratio is usually a (an)...
Circuit Breaker.
Isolation transformer.
200 volts AC.
Cut around clothing that has adhered to the burned area.

29. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The motor rotation is reversed.
They should be made by the same manufacturer.

30. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Four times less than that of the secondary.
A.C.
Allow for metering voltage and Current.
No.6 AWG.

31. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
7 -630 volts.
They must be installed at least 7 feet above the ground.
Four times less than that of the secondary.
It provides good speed control.

32. What type motor is a wound-rotor induction motor?
7 -630 volts.
Allow for metering voltage and Current.
A.C.
Cut around clothing that has adhered to the burned area.

33. How do you change the direction of a 3-phase AC motor?
H terminals.
Nearly constant.
Reverse any two-phase leads.
277 volts.

34. When not connected to a load - the secondary leads of a current transformer should be...
The motor rotation is reversed.
7 -630 volts.
Derive a neutral for grounding purposes.
Shunted and taped

35. A control power transformer...
The capacitors should be discharged.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Tied together
100 turns.

36. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
H terminals.
12 to 15 times a minute.
60 Hertz

37. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
600 volts.
The current will read zero.
The chest should rise or inflate.
Continuous.

38. 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.
5:1.
5:1
Continuous.
Zero amps.

39. 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?
Squirrel-cage rotor.
600 volts.
3 -979 Volts.
Inductance.

40. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.
Inductance.
25 feet.

41. What should the duty rating of a grounding resistor be?
Continuous.
A grounding resistor.
75 turns.
Reverse its rotation.

42. Compared to the secondary of a loaded - step-down transformer - the primary has...
The chest should rise or inflate.
An electromagnet.
The sum of the two capacitors.
Lower current and higher voltage.

43. Not a symptom of electrical shock?.
Inductance.
Inductance.
Current changing constantly in magnitude and periodically in direction.
Hyperventilation.

44. 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...
A step-up transformer.
The capacitors should be discharged.
60 cycles per second (60 Hertz).
Draw less current.

45. Which of the following does a squirrel cage induction motor have?
Stator windings.
A step-up transformer.
Lower current and higher voltage.
Carotid pulse - which is located in the neck next to the Adam's apple.

46. What is the danger when working around capacitors?
Because less current flowing at high voltage causes less line loss per kilowatt.
800 volts.
Four times less than that of the secondary.
An electrical shock hazard may exist.

47. How should clothing be removed from a burn?
800 volts.
Cut around clothing that has adhered to the burned area.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
600 volts.

48. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Circuit Breaker.
A step-up transformer.
Capacitance.

49. 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.
800 volts.
200 volts AC.
The chest should rise or inflate.

50. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Second-degree burn.
Disconnect the frame-grounding conductor.
Grounded phase and ground fault devices were not operating.