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
On a marine vessel, what is the purpose of an isolation transformer in an AC shore power system?
Answer: To isolate the vessel's AC system from the shore ground, eliminating galvanic corrosion and shock hazard
An isolation transformer magnetically couples shore power to the vessel while isolating the vessel's AC neutral from the shore ground, eliminating stray current corrosion and electric shock drowning risk.
What condition does a marine technician identify when a battery shows 12.6V open circuit but drops below 9.6V under cranking load?
Answer: A sulfated or internally damaged battery with high internal resistance
A fully charged battery should hold above 9.6V during cranking; a severe drop indicates sulfation or internal damage causing high internal resistance.
Which wiring method is REQUIRED by ABYC standards for marine DC wiring installed below decks?
Answer: Tinned copper conductors to resist corrosion in the marine environment
ABYC standards require tinned copper conductors for marine wiring because the tin plating resists the corrosion caused by the marine environment's moisture and salt air.
A technician measures resistance between the vessel's DC negative bus and the engine block and finds 0 ohms. What does this indicate?
Answer: Normal wiring in a negative-ground DC system
In a negative-ground DC system, the engine block serves as the ground reference, so 0 ohms between the DC negative bus and engine block is the correct, expected condition.
When using a clamp-on ammeter to measure DC current in a marine circuit, what is the MOST important installation consideration?
Answer: The clamp must encircle only ONE conductor — either positive OR negative, not both
A clamp-on ammeter measures the magnetic field around a single conductor; clamping both conductors cancels the magnetic fields and results in a zero reading.
What type of corrosion occurs when two dissimilar metals are in electrical contact while submerged in seawater?
Answer: Galvanic corrosion
Galvanic corrosion occurs when dissimilar metals in electrical contact form a galvanic cell in an electrolyte (seawater), causing the less noble metal (anode) to corrode.
A marine vessel's tachometer reads erratically at all engine speeds. The signal wire, sender, and instrument all test good. What is the MOST likely remaining cause?
Answer: A poor ground connection at the tachometer or sender
A poor or intermittent ground connection is the most common cause of erratic gauge readings after all active components have tested good.