All 36 Ham Radio Technician questions for T0 Safety with the correct answers marked and a short explanation for each, from the official 2026-2030 question pool. Test yourself with the free practice exam.
T0A01
Which of the following is a safety hazard of a 12-volt storage battery that lacks internal protection circuitry?
A. Touching both terminals with your hands can cause electrical shock
B. Shorting the terminals can cause burns, fire, or an explosion ✓
C. RF emissions from a nearby transmitter can cause the electrolyte to emit poison gas
D. All these choices are correct
Why: A 12-volt battery can supply hundreds of amps if its terminals are shorted, heating wires or tools enough to cause burns, fire, or even an explosion. Twelve volts is generally too low to cause a dangerous shock.
T0A02
What health hazard is posed by electrical current flowing through the body?
A. It may cause injury by heating body tissue
B. It may disrupt the electrical functions of cells
C. It may cause involuntary muscle contractions
D. All these choices are correct ✓
Why: Current through the body can heat and burn tissue, disrupt the electrical signals of cells such as the heart, and cause involuntary muscle contractions that prevent letting go. All these hazards apply.
T0A03
In the United States, what circuit does black wire insulation indicate in a three-wire 120 V AC cable?
A. Neutral
B. Hot ✓
C. Equipment ground
D. Negative
Why: In US AC wiring, the black wire is the hot (live) conductor. White is neutral and green or bare copper is the equipment safety ground.
T0A04
What is the purpose of a fuse in an electrical circuit?
A. To prevent power supply ripple from damaging a component
B. To remove power in case of an overload ✓
C. To limit current and prevent shocks
D. All these choices are correct
Why: A fuse is a wire that melts and opens the circuit when too much current flows, removing power during an overload or short circuit. It does not prevent electric shock.
T0A05
Why should a 5-ampere fuse never be replaced with a 20-ampere fuse?
A. The larger fuse would be likely to blow because it is rated for higher current
B. The power supply ripple would greatly increase
C. Excessive current could cause a fire ✓
D. Voltage drop in the higher current fuse could result in excessively low voltage to the device
Why: A fuse protects the wiring and equipment by blowing at its rated current. A 20-amp fuse in a 5-amp circuit would let far too much current flow, possibly overheating the wiring and causing a fire.
T0A06
What is a good way to guard against electrical shock at your station?
A. Use three-wire cords and plugs for all AC powered equipment
B. Connect all AC powered station equipment to a common safety ground
C. Ensure all capacitors used for high-voltage DC are fully discharged before working inside equipment
D. All these choices are correct ✓
Why: Using three-wire cords and plugs, bonding all equipment to a common safety ground, and discharging high-voltage capacitors before working inside equipment all reduce shock risk. All choices are correct.
T0A07
Where should a lightning arrester be installed in a coaxial feed line?
A. At the output connector of a transceiver
B. At the antenna feed point
C. At the AC power service panel
D. On a grounded panel near where feed lines enter the building ✓
Why: Install the lightning arrester on a grounded panel where feed lines enter the building. That way lightning surges are diverted to ground before they reach equipment indoors.
T0A08
Where should a fuse or circuit breaker be installed in a 120V AC power circuit?
A. In series with the hot conductor only ✓
B. In series with the hot and neutral conductors
C. In parallel with the hot conductor only
D. In parallel with the hot and neutral conductors
Why: A fuse or circuit breaker goes in series with the hot conductor only. This way, an overload disconnects the hot wire, removing voltage from the equipment. Fusing the neutral could leave the equipment energized.
T0A09
What should be done to all external ground rods or earth connections?
A. Waterproof them with silicone caulk or electrical tape
B. Keep them as far apart as possible
C. Bond them together with heavy wire or conductive strap ✓
D. Tune them for resonance on the lowest frequency of operation
Why: All ground rods and earth connections should be bonded together with heavy wire or conductive strap. This keeps them at the same potential, preventing dangerous voltage differences during lightning or faults.
T0A10
What hazard exists when rapidly charging or discharging an unprotected battery?
A. Overheating or out-gassing ✓
B. Excess output ripple
C. Electric shock
D. Overvoltage
Why: Charging or discharging an unprotected battery too fast can make it overheat and release gases (out-gassing). This can damage the battery or cause fire or explosion.
T0A11
What hazard exists in a power supply immediately after turning it off?
A. Circulating currents in the dc filter
B. Leakage flux in the power transformer
C. Voltage transients from kickback diodes
D. Charge stored in filter capacitors ✓
Why: Power supply filter capacitors can hold a dangerous charge after the supply is switched off. Unless discharged by bleeder resistors or manually, they can deliver a shock.
T0A12
Which of the following precautions should be taken when measuring high voltages with a voltmeter?
A. Ensure that the voltmeter has very low impedance
B. Ensure that the voltmeter and its leads are rated for use at the voltages being measured ✓
C. Ensure that the circuit is grounded through the voltmeter
D. Ensure that the voltmeter is set to the correct frequency
Why: Measuring high voltage with meters or leads not rated for it can cause insulation breakdown, arcing or shock. Always use a voltmeter and leads rated for the voltage being measured.
T0B01
Which of the following is good practice when installing ground wires on a tower for lightning protection?
A. Put a drip loop in the ground connection to prevent water damage to the ground system
B. Make sure all ground wire bends are right angles
C. Ensure that connections are short and direct ✓
D. All these choices are correct
Why: Lightning current follows the lowest-impedance path. Short, direct ground connections with gentle curves (no sharp bends) give lightning the easiest path to ground.
T0B02
What is required when climbing an antenna tower?
A. Have sufficient training on safe tower climbing techniques
B. Use appropriate tie-off to the tower at all times
C. Always wear an approved climbing harness
D. All these choices are correct ✓
Why: Tower climbing requires proper training, an approved climbing harness, and tying off to the tower at all times to prevent falls. All these choices are required.
T0B03
Under what circumstances is it safe to climb a tower without a helper or observer?
A. When no electrical work is being performed
B. When no mechanical work is being performed
C. When the work being done is not more than 20 feet above the ground
D. Never ✓
Why: Never climb a tower without a helper or observer. If you fall or have trouble, someone needs to be there to help and call for assistance, regardless of height or type of work.
T0B04
Which of the following is an important safety precaution to observe when putting up an antenna tower?
A. Wear a ground strap connected to your wrist at all times
B. Insulate the base of the tower to avoid lightning strikes
C. Look for and stay clear of any overhead electrical wires ✓
D. All these choices are correct
Why: Contact with overhead power lines is a leading cause of fatal antenna accidents. Always look for and stay well clear of electrical wires when erecting a tower or antenna.
T0B05
What is the purpose of a safety wire through a turnbuckle used to tension guy lines?
A. Secure the guy line if the turnbuckle breaks
B. Prevent loosening of the turnbuckle from vibration ✓
C. Provide a ground path for lightning strikes
D. Provide an ability to measure for proper tensioning
Why: A safety wire threaded through a turnbuckle keeps it from slowly unscrewing due to vibration and wind, which would loosen the guy line.
T0B06
What is the minimum safe distance from a power line to allow when installing an antenna?
A. Add the height of the antenna to the height of the power line and multiply by a factor of 1.5
B. The height of the power line above ground
C. 1/2 wavelength at the operating frequency
D. Enough so that if the antenna falls, no part of it can come within 10 feet of the power wires ✓
Why: Place an antenna so that if it falls, no part of it can come within 10 feet of power lines. Contact with power lines can be fatal.
T0B07
Which of the following is an important safety rule to remember when using a crank-up tower?
A. This type of tower must never be painted
B. This type of tower must never be grounded
C. This type of tower must not be climbed unless it is retracted, or mechanical safety locking devices have been installed ✓
D. All these choices are correct
Why: A crank-up tower can collapse if its cables or winch fail. Never climb it unless it is fully retracted or mechanical safety locking devices are installed to hold the sections in place.
T0B08
Which is a proper grounding method for a tower?
A. A single four-foot ground rod, driven into the ground no more than 12 inches from the base
B. A ferrite-core RF choke connected between the tower and ground
C. A connection between the tower base and a cold-water pipe
D. Separate eight-foot ground rods for each tower leg, bonded to the tower and each other ✓
Why: Proper tower grounding uses separate eight-foot ground rods for each tower leg, bonded to the tower and to each other. Water pipes and short rods are not adequate lightning grounds.
T0B09
Why should you avoid attaching an antenna to a utility pole?
A. The antenna will not work properly because of induced voltages
B. The antenna may unbalance the power transformer, causing power fluctuations
C. The antenna could contact high-voltage power lines ✓
D. All these choices are correct
Why: Utility poles carry high-voltage power lines. An antenna mounted on a pole could contact those lines, creating a shock or electrocution hazard. Utility poles also belong to the utility company.
T0B10
Which of the following is true when installing grounding conductors used for lightning protection?
A. Use only non-insulated wire
B. Wires must be carefully routed with precise right-angle bends
C. Sharp bends must be avoided ✓
D. Common grounds must be avoided
Why: Lightning, with its fast rise time, does not follow sharp bends well and may jump to other objects. Grounding conductors should be routed with gentle curves and no sharp bends.
T0B11
Which of the following establishes grounding requirements for an amateur radio tower or antenna?
A. FCC Part 97 rules
B. Local electrical codes ✓
C. FAA tower lighting regulations
D. UL recommended practices
Why: Grounding requirements for towers and antennas are set by local electrical codes, often based on the National Electrical Code. FCC Part 97 does not set grounding rules.
T0C01
What type of radiation are radio signals?
A. Gamma radiation
B. Ionizing radiation
C. Alpha radiation
D. Non-ionizing radiation ✓
Why: Radio waves are non-ionizing radiation: their photons lack the energy to remove electrons from atoms. Gamma rays and alpha particles are ionizing radiation.
T0C02
Which of the following bands has the lowest maximum permissible exposure for RF safety?
A. 3.5 MHz
B. 50 MHz ✓
C. 440 MHz
D. 1296 MHz
Why: The human body absorbs RF energy most efficiently in the 30 to 300 MHz range. So the maximum permissible exposure limits are lowest there, and 50 MHz falls in that range.
T0C03
How does the allowable power density for RF safety change if duty cycle changes from 100 percent to 50 percent?
A. It increases by a factor of 3
B. It decreases by 50 percent
C. It increases by a factor of 2 ✓
D. There is no adjustment allowed for lower duty cycle
Why: Exposure limits are based on average power. At a 50 percent duty cycle, average power is halved, so the allowable power density increases by a factor of 2 compared with 100 percent duty cycle.
T0C04
What factors affect the RF exposure of people near an amateur station antenna?
A. Frequency and power level of the RF field
B. Distance from the antenna to a person
C. Radiation pattern of the antenna
D. All these choices are correct ✓
Why: RF exposure depends on the frequency and power level, the distance from the antenna, and the antenna's radiation pattern. All these choices affect exposure.
T0C05
Why do exposure limits vary with frequency?
A. Lower frequency RF fields have more energy than higher frequency fields
B. Lower frequency RF fields do not penetrate the human body
C. Higher frequency RF fields are transient in nature
D. The human body absorbs more RF energy at some frequencies than at others ✓
Why: The body absorbs RF energy differently depending on frequency, absorbing most in the 30 to 300 MHz range where body dimensions relate to wavelength. So exposure limits vary by frequency.
T0C06
Which of the following is an acceptable method to determine whether your station complies with FCC RF exposure regulations?
A. By calculation based on FCC OET Bulletin 65
B. By calculation based on computer modeling
C. By measurement of field strength using calibrated equipment
D. All these choices are correct ✓
Why: FCC rules allow you to evaluate RF exposure by calculations based on OET Bulletin 65, by computer modeling, or by measuring field strength with calibrated equipment. All are acceptable.
T0C07
What hazard is created by touching an antenna during a transmission?
A. Electrocution
B. RF burn to skin ✓
C. Exposure to ionizing radiation
D. All these choices are correct
Why: Touching an antenna while transmitting can cause an RF burn where RF current flows into your skin. High-power RF can heat tissue quickly. It is not ionizing radiation.
T0C08
Which of the following actions can reduce exposure to RF radiation?
A. Relocate antennas ✓
B. Relocate the transmitter
C. Increase the duty cycle
D. All these choices are correct
Why: Moving antennas farther from people reduces the RF field strength they experience. Relocating the transmitter alone does not change where RF is radiated, and increasing duty cycle increases exposure.
T0C09
How can you make sure your station stays in compliance with RF safety regulations?
A. By informing the FCC of any changes made in your station
B. By re-evaluating the station whenever an item in the transmitter or antenna system is changed ✓
C. By making sure your antennas have low SWR
D. By using only Underwriter Laboratories approved transmitting equipment
Why: Any change to your transmitter, power, frequency, or antenna system can change RF exposure, so you should re-evaluate your station whenever such an item changes. There is no FCC notification requirement.
T0C10
Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?
A. It affects the average exposure to radiation ✓
B. It affects the peak exposure to radiation
C. It takes into account the antenna feed line loss
D. It takes into account the thermal effects of the final amplifier
Why: RF exposure limits are based on average exposure over time. Duty cycle, the fraction of time transmitting, determines that average, so a lower duty cycle means less average exposure.
T0C11
What is the definition of duty cycle during the averaging time for RF exposure?
A. The difference between the lowest and highest power output of a transmitter
B. The difference between the PEP and the average power output of a transmitter
C. The percentage of time that a transmitter is transmitting ✓
D. The percentage of time that a transmitter is not transmitting
Why: Duty cycle is the percentage of time the transmitter is transmitting during the averaging period. For example, transmitting for half the time is a 50 percent duty cycle.
T0C12
How does RF radiation differ from ionizing radiation (radioactivity)?
A. RF radiation does not have sufficient energy to cause chemical changes in cells and damage DNA ✓
B. RF radiation can only be detected with an RF dosimeter
C. RF radiation is limited in range to a few feet
D. RF radiation is perfectly safe
Why: RF energy is non-ionizing: it lacks the energy to break chemical bonds or damage DNA, unlike X-rays or radioactivity. Its main hazard is heating tissue, so it is not perfectly safe.
T0C13
Who is responsible for ensuring that no person is exposed to RF energy above the FCC exposure limits?
A. The FCC
B. The station licensee ✓
C. Anyone who is near an antenna
D. The local zoning board
Why: The station licensee is responsible for ensuring no person is exposed to RF energy above FCC limits. That means evaluating the station and taking steps to protect others.