Engine Electrical Systems practice questions

Answer: A) The brushes have worn to the minimum length specified by the manufacturer

Generator brushes wear in service. They are inspected and replaced when worn to the manufacturer's minimum length. A brown commutator film and properly seated brushes are normal conditions.

• ACorrect. Brushes wear in service. They are measured during inspection and replaced when they reach the manufacturer's minimum allowable length.
• BIncorrect. A smooth, even brown film on the commutator is normal and shows good brush-to-commutator contact. It is not a reason to replace the brushes.
• CIncorrect. Brushes are replaced based on measured wear against the manufacturer's limits, not tied to oil change intervals.
• DIncorrect. Brush faces are supposed to seat to the commutator's curvature. This gives full contact and is the desired condition, not a defect.

Answer: B) Starts, then generates power

• AIncorrect. It also generates power.
• BCorrect. One unit saves weight.
• CIncorrect. It's usually DC.
• DIncorrect. It drives the engine for starting.

Answer: D) That generator is offline

• AIncorrect. Balanced loads show similar readings.
• BIncorrect. This is not shown by a zero reading.
• CIncorrect. The zero side is the suspect.
• DCorrect. A zero load reading usually means that generator is not supplying the bus.

Answer: A) The starter relay is stuck closed

• ACorrect. The starter may keep running and overheat.
• BIncorrect. The light should go out.
• CIncorrect. That isn't the indication.
• DIncorrect. That's a separate light.

Answer: B) Power critical loads in emergencies

• AIncorrect. Those are nonessential.
• BCorrect. It can run from the battery alone.
• CIncorrect. It carries critical loads.
• DIncorrect. That isn't its role.

Answer: A) Voltage, frequency, and phase sequence

Paralleling AC generators requires matched voltage, frequency, and phase sequence/relationship so they can share load without damaging circulating currents.

• ACorrect. If voltage, frequency, and phase relationship/sequence don't match, large circulating currents and transients flow when the generators are tied. A reversed phase sequence keeps a generator from synchronizing at all.
• BIncorrect. Load current and power factor depend on the connected loads after paralleling. They are not conditions that must be matched first, and this set leaves out frequency and phase.
• CIncorrect. Generators with different ratings or field resistance can still be paralleled. Voltage and phase sequence, which this set leaves out, must match.
• DIncorrect. Drive speed rating and frame size are design features, not electrical conditions that are synchronized before closing the bus tie.

Answer: D) Opens when generator voltage drops

• AIncorrect. That's the starter solenoid.
• BIncorrect. That's the regulator.
• CIncorrect. That's a current limiter.
• DCorrect. It disconnects the generator below battery voltage, so it stops the battery from motoring the generator.

Answer: D) Low resistance one way

• AIncorrect. A good diode reads differently.
• BIncorrect. That is a shorted diode.
• CIncorrect. That is an open diode.
• DCorrect. A good diode conducts in one direction and blocks in the other.

Answer: B) Can be reset after it trips

• AIncorrect. It opens on overload.
• BCorrect. A fuse must be replaced.
• CIncorrect. Both are used in AC and DC.
• DIncorrect. It protects the circuit.

Answer: A) Loads don't exceed generator capacity

• ACorrect. Battery capacity for emergencies is checked too.
• BIncorrect. Gauges vary by load.
• CIncorrect. That's weight and balance.
• DIncorrect. That isn't electrical.