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. Current that changes periodically in direction is...
480 volts.
Capacitance.
Alternating current.
600 volts.

2. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Carotid pulse - which is located in the neck next to the Adam's apple.
Electro-magnetism for their operation.
The current will read zero.

3. The standard frequency of power supplied by the power company is...
The capacitors should be discharged.
60 cycles per second (60 Hertz).
Capacitance.
An electrical shock hazard may exist.

4. 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...
Grounded phase and ground fault devices were not operating.
Draw less current.
Larger than that found in the primary winding.
60 Hertz

5. AC voltage is raised or lowered by means of...
Circuit Breaker.
Transformers.
Squirrel-cage induction motor.
75 turns.

6. At what rate should mouth-to-mouth resuscitation be applied?
60 Hertz
The sum of the two capacitors.
Because less current flowing at high voltage causes less line loss per kilowatt.
12 to 15 times a minute.

7. What type motor is a wound-rotor induction motor?
Tied together
No.6 AWG.
Reverse its rotation.
A.C.

8. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
25 feet.
Second-degree burn.
3 -979 Volts.
Zero amps.

9. The size of a transformer is measured in...
75 turns.
At least two phases
Kilovolt ampere (KVA).
Capacitance.

10. 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...
Circuit Breaker.
Transformers.
Tied together
75 turns.

11. High voltage is used to transmit power over long distances...
25 feet.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.

12. 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?
Isolation transformer.
A step-up transformer.
3 -979 Volts.
15 feet off the ground.

13. 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.
Zero amps.
5:1
They must be installed at least 7 feet above the ground.
75 turns.

14. A transformer with a 1:1 ratio is usually a (an)...
1 amp.
Isolation transformer.
A.C.
200 volts AC.

15. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
X.
Electro-magnetism for their operation.
Short-circuited after power has been removed.

16. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Kilovolt ampere (KVA).
277 volts.
2000 watts

17. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Lower current and higher voltage.
12 to 15 times a minute.
They should be made by the same manufacturer.
5:1.

18. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
At least two phases
Check to make sure that the victim is not still in contact with the electricity.
7 -630 volts.
Current that changes constantly in magnitude and periodically in direction.

19. The combined capacitance of two capacitors in parallel is...
An electrical shock hazard may exist.
The sum of the two capacitors.
Kilovolt ampere (KVA).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

20. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
25 feet.
2000 watts
The current will read zero.
800 volts.

21. Not true about AC power?
An electromagnet.
5:1.
It provides good speed control.
They should be made by the same manufacturer.

22. 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.C.
Draw less current.
They must be installed at least 7 feet above the ground.
Reverse any two-phase leads.

23. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
3 -979 Volts.
480 volts.
H terminals.

24. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Nearly constant.
They should be made by the same manufacturer.
It provides good speed control.

25. A burn causing a blister is classified as a...
Short-circuited after power has been removed.
Second-degree burn.
Provides single-phase power to smaller loads such as lights - heaters - etc.
150 turns.

26. What should the duty rating of a grounding resistor be?
Disconnect the frame-grounding conductor.
25 feet.
Continuous.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

27. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
H terminals.
A grounding resistor.
An electromagnet.
They should be made by the same manufacturer.

28. 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...
A step-up transformer.
A device used to store electrical energy.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 volts.

29. What is a capacitor?
The current will read zero.
Inductance.
Check to make sure that the victim is not still in contact with the electricity.
A device used to store electrical energy.

30. The purpose of a zig-zag transformer is to...
Because less current flowing at high voltage causes less line loss per kilowatt.
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.
Draw less current.

31. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
15 feet off the ground.
Zero amps.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Isolation transformer.

32. Not a symptom of electrical shock?.
Transformers.
Lower current and higher voltage.
They should be made by the same manufacturer.
Hyperventilation.

33. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Two speeds
Carotid pulse - which is located in the neck next to the Adam's apple.
480 volts.
Draw less current.

34. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
600 volts.
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage.

35. Current transformers - or CT's - are used to...
600 volts.
200 volts AC.
7 -630 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

36. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Isolation transformer.
Check to make sure that the victim is not still in contact with the electricity.
Current changing constantly in magnitude and periodically in direction.

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?
200 volts AC.
Squirrel-cage rotor.
Potential transformer.
12 to 15 times a minute.

38. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
75 turns.
Cut around clothing that has adhered to the burned area.
2000 watts
They must be installed at least 7 feet above the ground.

39. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Shunted and taped
Disconnect the frame-grounding conductor.
At the source transformer.
Four times less than that of the secondary.

40. What steps up or steps down AC voltage?
200 volts AC.
Transformer
H terminals.
The current will read zero.

41. How should clothing be removed from a burn?
Lower current and higher voltage
Cut around clothing that has adhered to the burned area.
Grounded phase and ground fault devices were not operating.
Larger than that found in the primary winding.

42. Compared to the secondary of a loaded - step-down transformer - the primary has...
Electro-magnetism for their operation.
A grounding resistor.
Inductance.
Lower current and higher voltage.

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

44. A transformer with 3000 turns in the primary winding has a primary voltage of 4 -800 volts and a secondary voltage of 240 volts. How many turns are in the secondary winding?
200 volts AC.
150 turns.
Zero amps.
277 volts.

45. 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.
Reverse any two-phase leads.
A step-up transformer.
No.6 AWG.

46. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
A device used to store electrical energy.
Disconnect the frame-grounding conductor.
60 Hertz

47. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Because less current flowing at high voltage causes less line loss per kilowatt.
Continuous.
277 volts.
Grounded phase and ground fault devices were not operating.

48. A wound-rotor induction motor has all the following EXCEPT...
Stator windings.
Squirrel-cage rotor.
100 volts.
3 -979 Volts.

49. 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?
Transformers.
75 turns.
Squirrel-cage induction motor.
3 -979 Volts.

50. A solenoid coil is...
60 cycles per second (60 Hertz).
12 to 15 times a minute.
An electromagnet.
A.C.