SAMS Vessel Electrical Systems 3 — Questions and Answers
Question 1: During a survey, you discover that a vessel's DC wiring uses automotive-grade wire throughout. The primary deficiency of automotive wire in the marine environment is:
- Lower voltage rating than marine-grade wire
- Lack of tinned conductors, making it susceptible to corrosion in humid conditions (Correct answer)
- Inability to carry sufficient amperage for marine loads
- Non-compliance with USCG color coding requirements
Correct answer: Lack of tinned conductors, making it susceptible to corrosion in humid conditions
Marine-grade wire uses tinned copper conductors to resist corrosion from moisture and salt air; automotive wire uses bare copper that corrodes in the marine environment.
Question 2: Stray current corrosion on a vessel is most effectively detected during a survey by:
- Measuring AC voltage between hull fittings with a multimeter
- Using a silver/silver-chloride reference electrode to measure hull potential in the water (Correct answer)
- Checking battery terminal color changes
- Inspecting the shore power cord for discoloration
Correct answer: Using a silver/silver-chloride reference electrode to measure hull potential in the water
A silver/silver-chloride reference electrode placed in the water adjacent to the vessel measures electrical potential and reveals stray current activity.
Question 3: A vessel's battery bank shows a resting voltage of 12.0V after 24 hours off charge. This indicates the batteries are approximately:
- Fully charged at 100%
- At approximately 50% state of charge (Correct answer)
- Completely discharged and damaged
- At approximately 75% state of charge
Correct answer: At approximately 50% state of charge
A 12V lead-acid battery at 12.0V resting voltage is typically at approximately 50% state of charge, indicating significant depletion.
Question 4: When evaluating a vessel's AC shore power system, a surveyor finds that the neutral and ground conductors are bonded together at the shore power inlet. This is:
- Correct and required by ABYC E-11 for proper grounding
- A serious deficiency that can cause shock hazard and galvanic corrosion (Correct answer)
- Acceptable only on vessels under 26 feet
- Required only when shore power exceeds 30 amps
Correct answer: A serious deficiency that can cause shock hazard and galvanic corrosion
Bonding neutral and ground at the shore power inlet on a vessel (rather than only at the source) creates a shock hazard and promotes galvanic corrosion through ground current flow.
Question 5: A vessel is equipped with an isolation transformer for shore power. The primary benefit of this installation for the marine surveyor to note is:
- It increases shore power voltage to 240V automatically
- It isolates the vessel's AC system from shore ground, eliminating a galvanic corrosion path (Correct answer)
- It provides backup power when shore power is unavailable
- It reduces the shore power amperage draw by 50%
Correct answer: It isolates the vessel's AC system from shore ground, eliminating a galvanic corrosion path
An isolation transformer breaks the galvanic connection between the vessel's underwater metals and shore ground, preventing galvanic corrosion through the shore power cable.
Question 6: ABYC E-11 requires that all ungrounded conductors in a vessel's DC system be protected by an overcurrent device located within:
- 7 inches of the power source
- 72 inches of the power source or where the wire leaves a protected enclosure (Correct answer)
- 12 inches of any terminal connection
- 24 inches of the battery switch
Correct answer: 72 inches of the power source or where the wire leaves a protected enclosure
ABYC E-11 requires overcurrent protection within 72 inches (7 feet) of the power source connection to limit the length of unprotected wiring.
Question 7: During inspection, a surveyor finds multiple circuits connected to a single battery terminal stud with a 'ring terminal stack.' This installation raises concern because:
- Ring terminals are not approved for marine use by ABYC
- Stacked terminals can create high-resistance connections and make circuit isolation impossible (Correct answer)
- Battery studs are rated for only one conductor under USCG regulations
- This arrangement bypasses the battery switch
Correct answer: Stacked terminals can create high-resistance connections and make circuit isolation impossible
Stacking multiple ring terminals on a single stud creates resistance and makes it impossible to isolate individual circuits without disconnecting all circuits at that point.
SAMS Vessel Electrical Systems 3
During a survey, you discover that a vessel's DC wiring uses automotive-grade wire throughout.
The primary deficiency of automotive wire in the marine environment is: