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Electricity - USCG Exam Questions

Marine electrical systems: motors and generators, switchboards and distribution, batteries, electronics, and control engineering.

Every question below is a real U.S. Coast Guard exam question with four choices. Answer one and the correct choice is revealed instantly, with the USCG reference and illustration where the question uses one.

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All Electricity questions

Questions 801–900 of 1,595 · page 9 of 16

  1. #802 If the driving torque, such as that produced by a diesel engine, creates pulsations when coupled with a synchronous generator operating in parallel, t...
  2. #803 How are AC and DC generators are similar?
  3. #804 A DC generator which is used to supply direct current in order to provide magnetizing current to an AC generator field is commonly known as what?
  4. #805 From the information given in the illustration, what would be the maximum output amperage available from the emergency generator if it operated with a... illustration
  5. #806 Which of the methods listed below is used to provide the rotational torque to cause an AC generator to turn?
  6. #807 How will the value of the output frequency change if the load is removed from a turbo generator having a governor speed droop setting of 3%?
  7. #808 From the information given in the illustration, which of the following statements is correct? EL-0106 illustration
  8. #809 Two AC generators are operating in parallel and both are equipped with automatic voltage regulators. While standing watch, one generator is noted as h...
  9. #810 When paralleling two alternators the synchronizing lamps grow dim and are totally darkened as the synchroscope pointer approaches the 0° position. Wha...
  10. #811 While paralleling two (2) AC generators using synchronizing lamps only, when will both lamps will go dark?
  11. #812 Diesel generators #1 and #2 are operating in parallel at near full load capacity. Diesel generator #1 suddenly trips out mechanically due to low lube...
  12. #813 When shore power is being connected to a ship in dry dock, what must be ensured, assuming that the ship's generators are rated at 450 VAC, 60Hz with a...
  13. #814 Upon failure of the normal power supply, by what means is the emergency generator placed on the line and connected to the emergency bus?
  14. #815 By what means is an AC generator prevented from becoming motorized?
  15. #816 As shown in the illustration of a DC machine which is configured as a generator, what is the polarity of the interpoles as compared to the main field... illustration
  16. #817 What is the purpose of the commutator and brushes on a DC generator?
  17. #818 Why are armature cores in a DC generator made of laminated steel sheets?
  18. #819 How are the field windings of a DC shunt generator connected?
  19. #820 In referring to the illustration of the elementary DC generator, what statement is true? EL-0028 illustration
  20. #821 In referring to the illustration of the Ward-Leonard drive system, what type of DC generator is used? EL-0153 illustration
  21. #822 What two factors determine the magnitude of the generated voltage of a DC generator?
  22. #823 For the purposes of generating a DC voltage, which of the following factors is subject to vary for a particular generator installation while in operat...
  23. #824 What statement is true concerning the use of commutating poles (also known as interpoles) in DC generators?
  24. #825 What statement is true concerning the use of compensating windings in DC generators?
  25. #826 What is the purpose of the series field used in a stabilized shunt DC generator?
  26. #827 With what device is the simplest method of controlling the terminal voltage of compound-wound DC generator?
  27. #828 Prior to closing the circuit breaker when paralleling two DC generators, what must you be certain of?
  28. #829 Which of the methods listed is used to maintain equal load sharing between two compound wound DC generators operating in parallel?
  29. #830 By what means is a DC generator prevented from becoming motorized if paralleling is accomplished without an equalizer?
  30. #831 How are fuses usually rated?
  31. #832 What is the characteristic that is associated with an "instantaneous-trip" single- element type fuse?
  32. #833 Due to the operating characteristics of the system, time lag fuses (or dual-element fuses) are necessary for use in what types of circuits?
  33. #834 Fuses are sometimes placed in series with a thermal trip-type circuit breaker. What is the purpose of a fuse used in this arrangement?
  34. #835 Which pair of safety disconnect switches shown in the illustration represents the exterior and interior views of a double throw switch? EL-0176 illustration
  35. #836 What is the basic similarity between a circuit breaker and a fuse?
  36. #837 The arc resulting from the tripping of a circuit breaker is prevented from damaging the contacts. How is this done?
  37. #838 A thermal-magnetic circuit breaker for a 300 KW alternator is rated at 500 amperes at full continuous load. Which of the following conditions will tri...
  38. #839 As shown in the illustration, which of the following pieces of equipment is supplied with a circuit breaker providing both overload and short-circuit... illustration
  39. #840 Which of the following pictures shown in the illustration is a control transformer, usually used to step down line voltage for supplying reduced volta... illustration
  40. #841 Relative to the number of turns of a secondary winding of a step-up transformer, what will be the number of turns of a primary winding?
  41. #842 If the primary winding of a voltage transformer is connected to a steady DC source, self-inductance and mutual inductance is not possible. As a result...
  42. #843 Which of the listed figures shown in the illustration represents a three phase transformer connected in a wye-wye configuration? EL-0084 illustration
  43. #844 What is the purpose of a potential transformer in an electric circuit?
  44. #845 Which of the following statements is true concerning step-down transformer operation?
  45. #846 When a transformer is used to step down voltage, what statement is true?
  46. #847 What is the primary purpose associated with the use of transformers onboard ships with AC generators?
  47. #848 An autotransformer is equipped with a 50% tap, a 65% tap, and an 80% tap. Which of the following statements is true concerning a load connected to the...
  48. #849 The transformer diagram shown in figure "B" of the illustration represents what type of transformer? EL-0082 illustration
  49. #850 If the illustrated device in figure "B" has a step-up ratio of 10 to 1 what voltage would be measured at the secondary shortly after the primary of th... illustration
  50. #851 Besides the fluorescent lamp itself and possibly a starter, which of the following components is included in a fluorescent lighting fixture?
  51. #852 What is the purpose of the inner phosphor coating of the fluorescent tube as shown in figure "A" of the illustration? EL-0081 illustration
  52. #853 Incandescent lamps are classified according to the shape of the bulb and the type of service, as well as the size and style of the base. How are incan...
  53. #854 Which of the following figures shown in the illustration represents incandescent lighting? EL-0122 illustration
  54. #855 How is electrical conductor insulation classed? Example: insulation class H
  55. #856 Which of the following materials is a good electrical insulator?
  56. #857 Which of the following is the only known perfect dielectric for the purpose of serving as electrical insulation?
  57. #858 What is "the voltage per millimeter of insulation thickness that the insulation can withstand without breaking down" called?
  58. #859 What happens to the life expectancy of insulation for each 10 C rise in operating temperature?
  59. #860 Why are large cable sizes often formed as individual conductors comprised of several smaller strands?
  60. #861 When electrical cables penetrate watertight bulkheads, what must be provided for?
  61. #862 Why is copper often used as an electrical conductor?
  62. #863 How are the line losses in a distribution circuit kept to a minimum?
  63. #864 In the diagram of the switchboard shown in the illustration, what is the purpose of the current transformers? EL-0003 illustration
  64. #865 What application would the switchboard instrumentation panel shown in the illustration best be suited for? EL-0040 illustration
  65. #866 Which of the following represents a characteristic of an ungrounded electrical distribution system?
  66. #867 In the diagram of the switchboard shown in the illustration, if one of the turbines should fail due to a throttle trip, what will happen? EL-0003 illustration
  67. #868 In the diagram of the switchboard shown in the illustration, what is the function of the device labeled "Gen. Bkr. Sw."? EL-0003 illustration
  68. #869 The timer element of a reverse power relay cannot be energized unless what condition is met?
  69. #870 How is a wattmeter electrically connected in a circuit?
  70. #871 What is the name of the part of the shipboard electrical system used to control the distribution of power to the branch circuits?
  71. #872 Upon failure of the normal power supply, how is the emergency generator placed on the line to feed power to the emergency bus?
  72. #873 In the illustration of the one line distribution system diagram, if the ship's service generator on line fails, what statement is true concerning the... illustration
  73. #874 What is a purpose of the automatic bus transfer device shown in the illustration? EL-0014 illustration
  74. #875 Referring to the containership one-line distribution diagram shown in the illustration, what is the purpose of the transformers providing power to the... illustration
  75. #876 Referring to the containership one-line distribution diagram shown in the illustration, what is the purpose of the feedback circuit breaker as used to... illustration
  76. #877 Referring to the containership one-line distribution diagram shown in the illustration, what statement is true concerning the battery charger? EL-0014 illustration
  77. #878 Which of the following statements concerning analog and digital devices is correct?
  78. #879 The multiplier prefix 'giga' (G) such as used in "gigabytes" represents what multiplication factor?
  79. #880 Which of the wave shapes shown in the illustration is termed a sinusoidal wave? EL-0088 illustration
  80. #881 As shown in the illustrated harmonic analysis diagram, which figure represents the fundamental (or first harmonic)? EL-0163 illustration
  81. #882 Which of the substances listed can be used to shield sensitive equipment from static magnetic fields?
  82. #883 When placed in a magnetic field, which of the materials listed will maintain the highest permeability?
  83. #884 Which line in figure "B" shown in the illustration represents the trailing edge of the wave? EL-0088 illustration
  84. #885 Which of the pictured solid state semiconductor devices is a light-emitting diode? EL-0068 illustration
  85. #886 A silicon controlled rectifier (SCR) is a solid state device used for what functional purpose?
  86. #887 What is the name of the semiconductor that decreases in resistance with an increase in temperature?
  87. #888 Which of the following statements correctly applies to bipolar junction transistors?
  88. #889 What does the symbol in figure "1" shown in the illustration represent? EL-0065 illustration
  89. #890 What is the name of the component labeled CR1 as shown in section "D" of the regulated DC power supply illustrated? EL-0085 illustration
  90. #891 In what applications are germanium semiconductor diodes commonly used?
  91. #892 In comparing a semiconductor diode to a vacuum tube diode, what statement is true?
  92. #893 What is the functional purpose of the resistor 'RL" placed in parallel to the output of a DC power supply as shown in section "D" of the regulated DC... illustration
  93. #894 Which of the following statements represents an application of a silicon controlled rectifier?
  94. #895 Silicon diodes which are designed for a specific reverse breakdown voltage, and are most often used as electronic power supply voltage regulators, are...
  95. #896 A signal derived from an amplifier output and returned to the amplifier input is called what type of signal?
  96. #897 In which section of the 24 VDC power supply circuit illustrated does the greatest change in voltage level take place when fed from 120 VAC ship's powe... illustration
  97. #898 What is the correct term for the fluctuation of voltages in figure "H" shown in the illustration? EL-0085 illustration
  98. #899 A common-emitter circuit has an input voltage of 0.1 volt, an output voltage of 2.0 volts, an input current of 0.5 milliamps, and an output current of...
  99. #900 What does the circuit shown in the illustration represent? EL-0085 illustration
  100. #901 The component labeled 'CR1' in the circuit shown in the illustration serves what functional purpose? EL-0085 illustration

Electricity questions: what to expect

Q How many Electricity questions are in the Engine pool?

There are 1,595 Electricity questions on this site, every one released by the U.S. Coast Guard or taken from the National Maritime Center's sample examinations, with its correct answer. The exam draws its Electricity module from the same pool.

Q What score do I need to pass the Electricity module?

Most USCG exam modules, including Electricity, require 70 percent to pass. Rules of the Road modules require 90 percent.

Q Are these the real USCG Electricity exam questions?

Yes. They are the published U.S. Coast Guard questions, matched to the National Maritime Center's 2026 sample examinations. Answer any question to see the correct choice, the USCG reference and the illustration where the question uses one.

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