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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 is the first step to be followed in aiding a victim of electrical shock?
Continuous.
The motor rotation is reversed.
At the source transformer.
Check to make sure that the victim is not still in contact with the electricity.

2. What steps up or steps down AC voltage?
H terminals.
277 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformer

3. The transformer used only to measure voltage is a...
Check to make sure that the victim is not still in contact with the electricity.
Kilovolt ampere (KVA).
A step-up transformer.
Potential transformer.

4. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
A grounding resistor.
Check to make sure that the victim is not still in contact with the electricity.
Capacitance.

5. 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.
A device used to store electrical energy.
Stator windings.
75 turns.

6. The combined capacitance of two capacitors in parallel is...
An electrical shock hazard may exist.
Hyperventilation.
The sum of the two capacitors.
X.

7. Current that changes periodically in direction is...
An electromagnet.
Short-circuited after power has been removed.
Alternating current.
The chest should rise or inflate.

8. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Shunted and taped
The current will read zero.
Stator windings.

9. Not an acceptable method for the installations of surface transformers?
Lower current and higher voltage
They must be installed at least 7 feet above the ground.
5:1.
A grounding resistor.

10. Three-phase AC underground cables must be provided with overcurrent protection using a...
277 volts.
Inductance.
1 amp.
Circuit Breaker.

11. What should the duty rating of a grounding resistor be?
Continuous.
The sum of the two capacitors.
Derive a neutral for grounding purposes.
Four times less than that of the secondary.

12. 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.
An electrical shock hazard may exist.
Reverse its rotation.
Derive a neutral for grounding purposes.

13. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
75 turns.
They should be made by the same manufacturer.
12 to 15 times a minute.
They must be installed at least 7 feet above the ground.

14. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Transformers.
25 feet.
A step-up transformer.
They should be made by the same manufacturer.

15. 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?
Isolation transformer.
Disconnect the frame-grounding conductor.
25 feet.
800 volts.

16. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Cut around clothing that has adhered to the burned area.
H terminals.
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.

17. The speed of an alternating current - squirrel-cage induction motor is...
3 -979 Volts.
Derive a neutral for grounding purposes.
Nearly constant.
The sum of the two capacitors.

18. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Current that changes constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
480 volts.

19. Not true about AC power?
Lower current and higher voltage.
It provides good speed control.
Current changing constantly in magnitude and periodically in direction.
Inductance.

20. The property of an electric circuit that opposes any change in current is called...
Inductance.
A grounding resistor.
Cut around clothing that has adhered to the burned area.
Continuous.

21. When not connected to a load - the secondary leads of a current transformer should be...
Clamp-on ammeter.
Disconnect the frame-grounding conductor.
15 feet off the ground.
Shunted and taped

22. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
75 turns.
Grounded phase and ground fault devices were not operating.
X.
The sum of the two capacitors.

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.
200 volts AC.
Squirrel-cage rotor.

24. To protect against over-current in a three-phase circuit over-current protection must be provided for...
An electromagnet.
100 volts.
Full-load - three-phase voltage.
At least two phases

25. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
800 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Derive a neutral for grounding purposes.
Short-circuited after power has been removed.

26. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The current will read zero.
Disconnect the frame-grounding conductor.
The capacitors should be discharged.
Capacitance.

27. A transformer with a 1:1 ratio is usually a (an)...
75 turns.
150 turns.
800 volts.
Isolation transformer.

28. Compared to the secondary of a loaded - step-down transformer - the primary has...
The motor rotation is reversed.
A grounding resistor.
Lower current and higher voltage.
Shunted and taped

29. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
3 -979 Volts.
At the source transformer.
A.C.

30. Current transformers - or CT's - are used to...
Reverse its rotation.
Full-load - three-phase voltage.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
An electromagnet.

31. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Capacitance.
Hyperventilation.
150 turns.

32. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
X.
25 feet.
75 turns.
A grounding resistor.

33. 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?
3 -979 Volts.
The capacitors should be discharged.
A step-up transformer.
Allow for metering voltage and Current.

34. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Second-degree burn.
100 volts.
Transformers.
The motor rotation is reversed.

35. Where should grounding resistors be located?
75 turns.
At the source transformer.
Electro-magnetism for their operation.
Squirrel-cage induction motor.

36. 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?
Squirrel-cage rotor.
A grounding resistor.
The current will read zero.
75 turns.

37. 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.
600 volts.
X.
25 feet.

38. 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.
12 to 15 times a minute.
Cut around clothing that has adhered to the burned area.
They must be installed at least 7 feet above the ground.

39. How should clothing be removed from a burn?
Disconnect the frame-grounding conductor.
Cut around clothing that has adhered to the burned area.
Shunted and taped
Reverse any two-phase leads.

40. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
5:1.
Four times less than that of the secondary.
3 -979 Volts.
Reverse any two-phase leads.

41. If any two-phase wires are reversed on a three-phase motor - the motor will...
Cut around clothing that has adhered to the burned area.
Reverse its rotation.
Hyperventilation.
The chest should rise or inflate.

42. 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.
A device used to store electrical energy.
The capacitors should be discharged.
The chest should rise or inflate.
5:1

43. AC voltage is raised or lowered by means of...
Transformers.
600 volts.
Inductance.
Grounded phase and ground fault devices were not operating.

44. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
60 cycles per second (60 Hertz).
15 feet off the ground.
Stator windings.
A device used to store electrical energy.

45. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
75 turns.
150 turns.
3 -979 Volts.

46. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage induction motor.
A grounding resistor.
Grounded phase and ground fault devices were not operating.

47. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
800 volts.
Current that changes constantly in magnitude and periodically in direction.
The chest should rise or inflate.
The current will read zero.

48. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Allow for metering voltage and Current.
Kilovolt ampere (KVA).
The capacitors should be discharged.

49. 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...
The chest should rise or inflate.
Allow for metering voltage and Current.
15 feet off the ground.
Draw less current.

50. Not a symptom of electrical shock?.
Carotid pulse - which is located in the neck next to the Adam's apple.
Hyperventilation.
Reverse its rotation.
Zero amps.