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. Compared to the secondary of a loaded - step-down transformer - the primary has...
Alternating current.
Lower current and higher voltage
Nearly constant.
480 volts.

2. 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...
Derive a neutral for grounding purposes.
Short-circuited after power has been removed.
Allow for metering voltage and Current.
Draw less current.

3. Define alternating current...
Clamp-on ammeter.
100 volts.
Current changing constantly in magnitude and periodically in direction.
A device used to store electrical energy.

4. Current transformers - or CT's - are used to...
480 volts.
75 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
2000 watts

5. What is a capacitor?
200 volts AC.
A device used to store electrical energy.
75 turns.
Hyperventilation.

6. What should the duty rating of a grounding resistor be?
Continuous.
Capacitance.
Derive a neutral for grounding purposes.
They should be made by the same manufacturer.

7. A burn causing a blister is classified as a...
200 volts AC.
Draw less current.
Four times less than that of the secondary.
Second-degree burn.

8. 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...
Electro-magnetism for their operation.
Two speeds
Kilovolt ampere (KVA).
100 volts.

9. What steps up or steps down AC voltage?
60 Hertz
Kilovolt ampere (KVA).
1 amp.
Transformer

10. 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?
The sum of the two capacitors.
The capacitors should be discharged.
Inductance.
3 -979 Volts.

11. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
5:1.
Full-load - three-phase voltage.
150 turns.

12. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Four times less than that of the secondary.
A step-up transformer.
800 volts.
15 feet off the ground.

13. The secondary windings on a 10:1 step-down transformer will have a wire size...
X.
Larger than that found in the primary winding.
Continuous.
At least two phases

14. Three-phase AC underground cables must be provided with overcurrent protection using a...
Two speeds
Circuit Breaker.
Current changing constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.

15. The property of an electrical circuit that opposes any change in voltage is called...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A.C.
Capacitance.
Draw less current.

16. The size of a transformer is measured in...
The capacitors should be discharged.
1 amp.
Kilovolt ampere (KVA).
15 feet off the ground.

17. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
They must be installed at least 7 feet above the ground.
An electrical shock hazard may exist.
75 turns.

18. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
It provides good speed control.
Squirrel-cage induction motor.
Inductance.

19. At what rate should mouth-to-mouth resuscitation be applied?
They should be made by the same manufacturer.
Allow for metering voltage and Current.
12 to 15 times a minute.
Current changing constantly in magnitude and periodically in direction.

20. 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?
Transformer
75 turns.
3 -979 Volts.
Derive a neutral for grounding purposes.

21. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Kilovolt ampere (KVA).
Squirrel-cage induction motor.
Lower current and higher voltage

22. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Allow for metering voltage and Current.
A.C.
25 feet.
Larger than that found in the primary winding.

23. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
7 -630 volts.
277 volts.
Larger than that found in the primary winding.
12 to 15 times a minute.

24. The combined capacitance of two capacitors in parallel is...
Provides single-phase power to smaller loads such as lights - heaters - etc.
A step-up transformer.
The sum of the two capacitors.
Current changing constantly in magnitude and periodically in direction.

25. 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.
Four times less than that of the secondary.
A step-up transformer.
An electrical shock hazard may exist.

26. The standard frequency of power supplied by the power company is...
1 amp.
Second-degree burn.
Potential transformer.
60 cycles per second (60 Hertz).

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

28. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
1 amp.
Continuous.
Two speeds
Nearly constant.

29. Which of the following does a squirrel cage induction motor have?
5:1
Derive a neutral for grounding purposes.
Stator windings.
3 -979 Volts.

30. What is the danger when working around capacitors?
Capacitance.
An electrical shock hazard may exist.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Alternating current.

31. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
A grounding resistor.
H terminals.
Inductance.

32. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
25 feet.
Nearly constant.
Lower current and higher voltage

33. All transformers step voltage up or down by...
Kilovolt ampere (KVA).
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.
Lower current and higher voltage

34. If any two-phase wires are reversed on a three-phase motor - the motor will...
Capacitance.
Reverse its rotation.
600 volts.
1 amp.

35. Current that changes periodically in direction is...
A step-up transformer.
Alternating current.
Current changing constantly in magnitude and periodically in direction.
They should be made by the same manufacturer.

36. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
No.6 AWG.
100 volts.
Short-circuited after power has been removed.
H terminals.

37. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Lower current and higher voltage.
Allow for metering voltage and Current.
Zero amps.

38. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
1 amp.
200 volts AC.
Full-load - three-phase voltage.

39. How should clothing be removed from a burn?
Electro-magnetism for their operation.
X.
Cut around clothing that has adhered to the burned area.
600 volts.

40. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
100 volts.
The chest should rise or inflate.
Transformer
Zero amps.

41. 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?
600 volts.
Tied together
100 volts.
Disconnect the frame-grounding conductor.

42. The main function of CT's and PT's on a main substation is to...
600 volts.
Allow for metering voltage and Current.
Clamp-on ammeter.
Stator windings.

43. 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?
Potential transformer.
75 turns.
277 volts.
Clamp-on ammeter.

44. The standard frequency of alternating current used at a mine is...
60 Hertz
277 volts.
No.6 AWG.
Grounded phase and ground fault devices were not operating.

45. What is the first step to be followed in aiding a victim of electrical shock?
7 -630 volts.
277 volts.
Check to make sure that the victim is not still in contact with the electricity.
200 volts AC.

46. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Four times less than that of the secondary.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current changing constantly in magnitude and periodically in direction.

47. 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...
They should be made by the same manufacturer.
Tied together
Shunted and taped
Reverse its rotation.

48. What type motor is a wound-rotor induction motor?
Clamp-on ammeter.
A.C.
Circuit Breaker.
Inductance.

49. Alternating current may be defined as...
Short-circuited after power has been removed.
480 volts.
Alternating current.
Current that changes constantly in magnitude and periodically in direction.

50. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
150 turns.
The motor rotation is reversed.
No.6 AWG.
Current changing constantly in magnitude and periodically in direction.