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Subel. T0
12 questions
Subelement T0

SAFETY

Section T0A

Power circuits and hazards: hazardous voltages, fuses and circuit breakers, grounding, electrical code compliance; Lightning protection; Battery safety

Which of the following is a safety hazard of a 12-volt storage battery that lacks internal protection circuitry?

  • Touching both terminals with your hands can cause electrical shock
  • Correct Answer
    Shorting the terminals can cause burns, fire, or an explosion
  • RF emissions from a nearby transmitter can cause the electrolyte to emit poison gas
  • All these choices are correct
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What health hazard is posed by electrical current flowing through the body?

  • It may cause injury by heating body tissue
  • It may disrupt the electrical functions of cells
  • It may cause involuntary muscle contractions
  • Correct Answer
    All these choices are correct
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In the United States, what circuit does black wire insulation indicate in a three-wire 120 V AC cable?

  • Neutral
  • Correct Answer
    Hot
  • Equipment ground
  • Negative
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What is the purpose of a fuse in an electrical circuit?

  • To prevent power supply ripple from damaging a component
  • Correct Answer
    To remove power in case of an overload
  • To limit current and prevent shocks
  • All these choices are correct
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Why should a 5-ampere fuse never be replaced with a 20-ampere fuse?

  • The larger fuse would be likely to blow because it is rated for higher current
  • The power supply ripple would greatly increase
  • Correct Answer
    Excessive current could cause a fire
  • Voltage drop in the higher current fuse could result in excessively low voltage to the device
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What is a good way to guard against electrical shock at your station?

  • Use three-wire cords and plugs for all AC powered equipment
  • Connect all AC powered station equipment to a common safety ground
  • Ensure all capacitors used for high-voltage DC are fully discharged before working inside equipment
  • Correct Answer
    All these choices are correct
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Where should a lightning arrester be installed in a coaxial feed line?

  • At the output connector of a transceiver
  • At the antenna feed point
  • At the AC power service panel
  • Correct Answer
    On a grounded panel near where feed lines enter the building
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Where should a fuse or circuit breaker be installed in a 120V AC power circuit?

  • Correct Answer
    In series with the hot conductor only
  • In series with the hot and neutral conductors
  • In parallel with the hot conductor only
  • In parallel with the hot and neutral conductors
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What should be done to all external ground rods or earth connections?

  • Waterproof them with silicone caulk or electrical tape
  • Keep them as far apart as possible
  • Correct Answer
    Bond them together with heavy wire or conductive strap
  • Tune them for resonance on the lowest frequency of operation
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What hazard occurs when rapidly charging or discharging an unprotected battery?

  • Correct Answer
    Overheating or out-gassing
  • Excess output ripple
  • Electric shock
  • Overvoltage
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What hazard exists in a power supply immediately after turning it off?

  • Circulating currents in the dc filter
  • Leakage flux in the power transformer
  • Voltage transients from kickback diodes
  • Correct Answer
    Charge stored in filter capacitors
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Which of the following precautions should be taken when measuring high voltages with a voltmeter?

  • Ensure that the voltmeter has very low impedance
  • Correct Answer
    Ensure that the voltmeter and its leads are rated for use at the voltages being measured
  • Ensure that the circuit is grounded through the voltmeter
  • Ensure that the voltmeter is set to the correct frequency
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