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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?
100 turns.
150 turns.
They should be made by the same manufacturer.
Check to make sure that the victim is not still in contact with the electricity.

2. The combined capacitance of two capacitors in parallel is...
Draw less current.
The sum of the two capacitors.
Clamp-on ammeter.
X.

3. Alternating current may be defined as...
2000 watts
Current that changes constantly in magnitude and periodically in direction.
Draw less current.
The capacitors should be discharged.

4. 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?
100 turns.
Inductance.
Two speeds
3 -979 Volts.

5. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.
3 -979 Volts.
480 volts.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
Draw less current.
Allow for metering voltage and Current.
Lower current and higher voltage.
Electro-magnetism for their operation.

7. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
H terminals.
X.
A.C.
60 cycles per second (60 Hertz).

8. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Disconnect the frame-grounding conductor.
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.

9. 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?
No.6 AWG.
150 turns.
Potential transformer.
Short-circuited after power has been removed.

10. 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.
An electrical shock hazard may exist.
15 feet off the ground.
A grounding resistor.

11. 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.
Isolation transformer.
5:1
Potential transformer.
Two speeds

12. Not true about AC power?
It provides good speed control.
An electrical shock hazard may exist.
15 feet off the ground.
Transformer

13. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
Larger than that found in the primary winding.
480 volts.

14. Not an acceptable method for the installations of surface transformers?
15 feet off the ground.
They must be installed at least 7 feet above the ground.
Potential transformer.
Two speeds

15. 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...
Zero amps.
100 volts.
Full-load - three-phase voltage.
A step-up transformer.

16. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Current changing constantly in magnitude and periodically in direction.
A.C.
A grounding resistor.
Squirrel-cage induction motor.

17. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
A device used to store electrical energy.
They should be made by the same manufacturer.
600 volts.
Nearly constant.

18. Operating coils - motors - transformers - relays and solenoids depend upon...
Current that changes constantly in magnitude and periodically in direction.
277 volts.
Electro-magnetism for their operation.
Zero amps.

19. 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...
Draw less current.
480 volts.
60 Hertz
3 -979 Volts.

20. A solenoid coil is...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current changing constantly in magnitude and periodically in direction.
2000 watts
An electromagnet.

21. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
480 volts.
Check to make sure that the victim is not still in contact with the electricity.
A.C.
A step-up transformer.

22. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Full-load - three-phase voltage.
7 -630 volts.
Zero amps.
Cut around clothing that has adhered to the burned area.

23. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
480 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Continuous.

24. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
A.C.
The motor rotation is reversed.
1 amp.

25. When not connected to a load - the secondary leads of a current transformer should be...
Draw less current.
Transformer
Provides single-phase power to smaller loads such as lights - heaters - etc.
Shunted and taped

26. 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?
A grounding resistor.
Derive a neutral for grounding purposes.
H terminals.
800 volts.

27. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
5:1.
Second-degree burn.
A device used to store electrical energy.

28. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
25 feet.
The chest should rise or inflate.
Draw less current.
The sum of the two capacitors.

29. 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.
Continuous.
Zero amps.
Reverse any two-phase leads.

30. All transformers step voltage up or down by...
A device used to store electrical energy.
Four times less than that of the secondary.
Draw less current.
Inductance.

31. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Kilovolt ampere (KVA).
Squirrel-cage induction motor.
The sum of the two capacitors.

32. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Current changing constantly in magnitude and periodically in direction.
Clamp-on ammeter.
277 volts.

33. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
An electrical shock hazard may exist.
Kilovolt ampere (KVA).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

34. The property of an electric circuit that opposes any change in current is called...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Isolation transformer.
Inductance.
150 turns.

35. 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?
75 turns.
Transformer
Squirrel-cage induction motor.
A.C.

36. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
200 volts AC.
The motor rotation is reversed.
Lower current and higher voltage.
The capacitors should be discharged.

37. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Nearly constant.
The current will read zero.
75 turns.
60 Hertz

38. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage
150 turns.

39. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
3 -979 Volts.
Stator windings.
Two speeds
Transformer

40. What should the duty rating of a grounding resistor be?
Squirrel-cage rotor.
Continuous.
The chest should rise or inflate.
Clamp-on ammeter.

41. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
60 Hertz
At the source transformer.
75 turns.
480 volts.

42. A transformer with a 1:1 ratio is usually a (an)...
Clamp-on ammeter.
The capacitors should be discharged.
The current will read zero.
Isolation transformer.

43. AC voltage is raised or lowered by means of...
Short-circuited after power has been removed.
A device used to store electrical energy.
Four times less than that of the secondary.
Transformers.

44. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage
Reverse any two-phase leads.
800 volts.

45. The transformer used only to measure voltage is a...
Draw less current.
200 volts AC.
Potential transformer.
An electrical shock hazard may exist.

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

47. A burn causing a blister is classified as a...
Clamp-on ammeter.
Second-degree burn.
Zero amps.
Because less current flowing at high voltage causes less line loss per kilowatt.

48. The standard frequency of power supplied by the power company is...
5:1.
60 Hertz
60 cycles per second (60 Hertz).
Two speeds

49. What type motor is a wound-rotor induction motor?
Continuous.
It provides good speed control.
A.C.
At the source transformer.

50. Current transformers - or CT's - are used to...
5:1.
At least two phases
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.