Practice Test Geeks(MST) Marine Service Technician Practice Test
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Electrical Systems & Troubleshooting Flashcards

7 cards from real MST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Electrical Systems & Troubleshooting flashcards as text

  1. A vessel's navigation lights fail but the fuse is intact. A technician measures 12V at the fuse but 0V at the light socket. What does this indicate?

    Answer: There is an open circuit between the fuse and the socket

    Voltage present at the fuse but absent at the load indicates an open circuit — a broken wire or failed connector — between those two test points.

  2. What is the maximum allowable AC voltage drop for shore power circuits on a marine vessel per ABYC standards?

    Answer: 5%

    ABYC E-11 allows a maximum 5% voltage drop for AC circuits on marine vessels, compared to 3% for DC circuits.

  3. When a marine technician performs a resistance test on a fuel sender unit, what must be done FIRST?

    Answer: Disconnect the sender from the circuit before measuring resistance

    The component must be isolated from the circuit before resistance testing; measuring resistance in a live circuit will give inaccurate readings and may damage the meter.

  4. What does the term 'polarization index' refer to when testing marine electrical insulation?

    Answer: The ratio of insulation resistance measured at 10 minutes to resistance at 1 minute

    The polarization index is the 10-minute to 1-minute insulation resistance ratio; a ratio above 2.0 generally indicates good insulation condition.

  5. A shore power inlet on a vessel shows no power at the main panel despite shore power being connected. The technician confirms 120V at the inlet receptacle. What should be checked NEXT?

    Answer: The shore power circuit breaker and reverse polarity indicator

    The shore power circuit breaker at the main panel is the next logical component to check, and the reverse polarity indicator confirms correct wiring.

  6. What is the function of a galvanic isolator installed in a shore power system?

    Answer: It blocks low-voltage DC galvanic current on the AC safety ground while allowing AC fault current to flow

    A galvanic isolator uses diodes to block low-voltage DC galvanic current on the safety ground, preventing underwater corrosion while still allowing AC fault current to pass safely.

  7. A marine technician is testing a suspect relay. With the relay coil energized, the normally open (NO) contacts should show:

    Answer: Near zero resistance on an ohmmeter

    When the relay coil is energized, the normally open contacts close and should show near zero (continuity) resistance.