Learn/ Technician course/Module 10 of 10
Technician Course, Module 10: Nobody Gets Hurt
Covers NCVEC 2026-2030 Technician Pool, Subelement T0 (Safety). Three questions on your exam come from this material.
Ray's left forearm has a pale scar shaped like a wrench. "Battery. Nineteen eighty-something. I set a tool across the terminals of a big lead-acid and it welded itself there, glowing." He rolls the sleeve back down. "Every rule in this module is a story like that one, learned by somebody. Learn them from the stories instead."
10.1Electricity Bites
Start with Ray's scar. A 12-volt storage battery without internal protection cannot shock you through dry skin, but shorting its terminals can cause burns, fire, or an explosion, because a big battery will dump hundreds of amps into a dead short. Rapidly charging or discharging an unprotected battery brings its own hazard: overheating or out-gassing. Respect the amp-hours.
Current through the body is the actual killer, and it hurts you three ways at once: heating tissue, disrupting the electrical functions of cells, and causing involuntary muscle contractions. All of these, which is why the answer to "what does shock do" is everything on the list.
House wiring has a color code, and one color matters most: in US three-wire 120 V cable, black insulation is the hot wire. Treat it accordingly.
The fuse rules, now with their reasons:
- A fuse's purpose is to remove power in case of an overload.
- In a 120 V AC circuit, the fuse or breaker goes in series with the hot conductor only. Fusing the neutral could leave a circuit dead but still hot, a trap for the next person inside it.
- And the classic exam scenario: never replace a 5-amp fuse with a 20-amp fuse, because excessive current could cause a fire. The fuse was protecting the wire. A bigger fuse just gives the fire a head start. This is Module 3's ammo can question, now wearing its safety hat.
Guarding against shock in the shack is a package deal: use three-wire cords and plugs on all AC equipment, connect all AC-powered equipment to a common safety ground, and make sure high-voltage capacitors are discharged before working inside anything. All of these. That capacitor rule has teeth: a power supply immediately after being switched off still holds a hazard, the charge stored in its filter capacitors. Off is not the same as safe.
Lightning gets two rules. The lightning arrester in a coax feed line belongs on a grounded panel near where the feed lines enter the building, and all external ground rods and earth connections must be bonded together with heavy wire or conductive strap. Separate, unbonded grounds invite a strike to equalize them through your equipment.
One measurement rule closes the section: when measuring high voltages, ensure the voltmeter and its leads are rated for the voltages being measured. A meter rated for less becomes part of the circuit in the worst way.
Knowledge Check 10.1
Tap an answer. In your own words first, then check yourself.
1. Why must a blown 5-amp fuse never be replaced with a 20-amp fuse?
2. The power supply is switched off and unplugged. What hazard remains inside?
3. Where does a coax lightning arrester belong?
T0A the easy way: all 12 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T0A01 Which of the following is a safety hazard of a 12-volt storage battery that lacks internal protection circuitry?
Answer Shorting the terminals can cause burns, fire, or an explosion
Tip A bare battery can dump huge current if the terminals touch metal, and that heat means burns, fire, or a blast.
T0A02 What health hazard is posed by electrical current flowing through the body?
Answer All these choices are correct
Tip Current through the body can hurt in several ways at once, so the right answer is all of them.
T0A03 In the United States, what circuit does black wire insulation indicate in a three-wire 120 V AC cable?
Answer Hot
Tip In US house wiring, black is the hot wire, the live one you must respect.
T0A04 What is the purpose of a fuse in an electrical circuit?
Answer To remove power in case of an overload
Tip A fuse is a weak link on purpose. It blows and cuts the power before an overload starts a fire.
T0A05 Why should a 5-ampere fuse never be replaced with a 20-ampere fuse?
Answer Excessive current could cause a fire
Tip A bigger fuse lets too much current keep flowing, so wires overheat and can catch fire.
T0A06 What is a good way to guard against electrical shock at your station?
Answer All these choices are correct
Tip There are several smart habits for shock safety, so pick all of them.
T0A07 Where should a lightning arrester be installed in a coaxial feed line?
Answer On a grounded panel near where feed lines enter the building
Tip Put the lightning arrester on a grounded panel right where the feed lines come into the building, so a strike goes to ground outside.
T0A08 Where should a fuse or circuit breaker be installed in a 120V AC power circuit?
Answer In series with the hot conductor only
Tip The fuse goes in the hot wire only, so breaking it fully kills power to the gear.
T0A09 What should be done to all external ground rods or earth connections?
Answer Bond them together with heavy wire or conductive strap
Tip Tie all your ground rods together with heavy wire or strap so they act as one ground.
T0A10 What hazard exists when rapidly charging or discharging an unprotected battery?
Answer Overheating or out-gassing
Tip Charging or draining a battery too fast makes it overheat and vent gas, both dangerous.
T0A11 What hazard exists in a power supply immediately after turning it off?
Answer Charge stored in filter capacitors
Tip Filter capacitors can hold a charge after the switch is off, so the supply can still shock you.
T0A12 Which of the following precautions should be taken when measuring high voltages with a voltmeter?
Answer Ensure that the voltmeter and its leads are rated for use at the voltages being measured
Tip Make sure the meter and its leads are rated for the voltage, or they can arc over and hurt you.
10.2Gravity Is Also a Hazard
Antennas go up, and up is where the danger is.
The first rule outranks all others: look for and stay clear of overhead electrical wires before putting up any antenna, and never attach an antenna to a utility pole, because the antenna could contact high-voltage lines. Then the geometry rule: keep enough distance from power lines that if the antenna falls, no part of it comes within 10 feet of the wires. Plan the failure, not just the installation.
Tower work is a discipline, not a chore:
- Climbing requires sufficient training in safe climbing techniques, an approved climbing harness, and constant tie-off to the tower. All of these, always.
- Is it ever safe to climb without a helper or observer? Never. The exam answer and the real answer are the same word.
- A crank-up tower must not be climbed unless it is fully retracted or its mechanical safety locking devices are engaged. The sections of a crank-up are a guillotine held by a cable.
- The safety wire through a turnbuckle on guy lines prevents the turnbuckle from loosening due to vibration. Wind works hardware loose one gust at a time.
Tower grounding pulls together everything from 10.1: proper practice is a separate eight-foot ground rod for each tower leg, bonded to the tower and to each other. Lightning conductors want short, direct connections with sharp bends avoided, because lightning does not turn corners, it jumps them. And who sets the legal requirements for grounding your tower or antenna? Not the FCC: local electrical codes establish grounding requirements.
Knowledge Check 10.2
Tap an answer. In your own words first, then check yourself.
1. How far from power lines should an antenna be installed?
2. When may you climb a tower alone, without an observer?
3. What establishes the grounding requirements for your antenna installation?
T0B the easy way: all 11 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T0B01 Which of the following is good practice when installing ground wires on a tower for lightning protection?
Answer Ensure that connections are short and direct
Tip Keep tower ground wires short and straight so a lightning strike takes the fastest path to earth.
T0B02 What is required when climbing an antenna tower?
Answer All these choices are correct
Tip Climbing a tower safely means doing several things, so the answer is all of them.
T0B03 Under what circumstances is it safe to climb a tower without a helper or observer?
Answer Never
Tip Climbing a tower alone is never safe. Always have a helper or observer with you.
T0B04 Which of the following is an important safety precaution to observe when putting up an antenna tower?
Answer Look for and stay clear of any overhead electrical wires
Tip Before raising a tower, look up and stay clear of any overhead power lines.
T0B05 What is the purpose of a safety wire through a turnbuckle used to tension guy lines?
Answer Prevent loosening of the turnbuckle from vibration
Tip A safety wire through the turnbuckle stops it from unwinding as the wind shakes the guy lines.
T0B06 What is the minimum safe distance from a power line to allow when installing an antenna?
Answer Enough so that if the antenna falls, no part of it can come within 10 feet of the power wires
Tip Keep enough distance that even if the antenna falls, no part gets within 10 feet of a power line.
T0B07 Which of the following is an important safety rule to remember when using a crank-up tower?
Answer This type of tower must not be climbed unless it is retracted, or mechanical safety locking devices have been installed
Tip Only climb a crank-up tower when it is fully down or locked, so it cannot collapse on you.
T0B08 Which is a proper grounding method for a tower?
Answer Separate eight-foot ground rods for each tower leg, bonded to the tower and each other
Tip Give each tower leg its own eight-foot ground rod, all bonded together and to the tower.
T0B09 Why should you avoid attaching an antenna to a utility pole?
Answer The antenna could contact high-voltage power lines
Tip Skip the utility pole, because your antenna could touch the high-voltage lines up there.
T0B10 Which of the following is true when installing grounding conductors used for lightning protection?
Answer Sharp bends must be avoided
Tip Avoid sharp bends in lightning ground conductors so the surge flows straight to earth.
T0B11 Which of the following establishes grounding requirements for an amateur radio tower or antenna?
Answer Local electrical codes
Tip Your local electrical code sets the grounding rules for a tower or antenna, so check it.
10.3Living With RF
Last topic, and Ray frames it precisely, because imprecision in this area breeds both carelessness and panic.
Radio signals are non-ionizing radiation. The difference from ionizing radiation (radioactivity) is fundamental: RF does not have sufficient energy to cause chemical changes in cells and damage DNA. RF's hazard is thermal, heating tissue, which is real but manageable. Touch an antenna during a transmission and the injury is an RF burn to the skin, not electrocution.
Exposure limits exist, and they vary with frequency because the human body absorbs more RF energy at some frequencies than at others. The band with the lowest maximum permissible exposure, meaning the strictest limit, is around 50 MHz, because human bodies are unfortunately good antennas near those frequencies.
What determines a person's actual exposure near your antenna? Frequency and power, distance from the antenna, and the antenna's radiation pattern. All of these, which is why the practical way to reduce exposure is to relocate antennas: distance is the cheapest shielding there is, and antennas belong up and away from people.
Duty cycle matters because exposure limits are based on averages. Duty cycle is the percentage of time a transmitter is transmitting during the averaging period, and it affects the average exposure to radiation. Cut duty cycle from 100 percent to 50 percent and the allowable power density increases by a factor of 2. Listening half the time literally doubles your margin, and hams listen far more than half the time.
The compliance frame: acceptable ways to evaluate your station include calculation per FCC OET Bulletin 65, computer modeling, and field-strength measurement with calibrated equipment. All of these. Staying compliant means re-evaluating whenever you change anything in the transmitter or antenna system, and the person responsible for making sure nobody is exposed beyond the limits is the station licensee. You. The same answer as Module 1's control operator questions, wearing a hard hat.
Knowledge Check 10.3
Tap an answer. In your own words first, then check yourself.
1. How does RF radiation differ from radioactivity?
2. Reducing duty cycle from 100 percent to 50 percent does what to allowable power density?
3. Who is responsible for keeping RF exposure at your station within FCC limits?
T0C the easy way: all 13 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T0C01 What type of radiation are radio signals?
Answer Non-ionizing radiation
Tip Radio waves are non-ionizing, meaning they lack the energy to break apart atoms in your body.
T0C02 Which of the following bands has the lowest maximum permissible exposure for RF safety?
Answer 50 MHz
Tip The body soaks up RF most around 50 MHz, so that band has the lowest allowed exposure.
T0C03 How does the allowable power density for RF safety change if duty cycle changes from 100 percent to 50 percent?
Answer It increases by a factor of 2
Tip Cut the duty cycle in half and you may run twice the power density, so it goes up by 2.
T0C04 What factors affect the RF exposure of people near an amateur station antenna?
Answer All these choices are correct
Tip Many things change how much RF reaches people near an antenna, so the answer is all of them.
T0C05 Why do exposure limits vary with frequency?
Answer The human body absorbs more RF energy at some frequencies than at others
Tip Limits change with frequency because the body absorbs RF energy more at some frequencies than others.
T0C06 Which of the following is an acceptable method to determine whether your station complies with FCC RF exposure regulations?
Answer All these choices are correct
Tip There are several valid ways to check RF exposure compliance, so pick all of them.
T0C07 What hazard is created by touching an antenna during a transmission?
Answer RF burn to skin
Tip Touch a live antenna while transmitting and the RF can give you a painful burn on the skin.
T0C08 Which of the following actions can reduce exposure to RF radiation?
Answer Relocate antennas
Tip Moving your antennas farther from people is a simple way to lower their RF exposure.
T0C09 How can you make sure your station stays in compliance with RF safety regulations?
Answer By re-evaluating the station whenever an item in the transmitter or antenna system is changed
Tip Re-check your station for RF safety any time you change the transmitter or antenna system.
T0C10 Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?
Answer It affects the average exposure to radiation
Tip Duty cycle sets how much time you actually transmit, which drives the average exposure.
T0C11 What is the definition of duty cycle during the averaging time for RF exposure?
Answer The percentage of time that a transmitter is transmitting
Tip Duty cycle is just the percentage of the averaging time that the transmitter is actually on the air.
T0C12 How does RF radiation differ from ionizing radiation (radioactivity)?
Answer RF radiation does not have sufficient energy to cause chemical changes in cells and damage DNA
Tip Unlike ionizing radiation, RF lacks the energy to change cell chemistry or damage DNA.
T0C13 Who is responsible for ensuring that no person is exposed to RF energy above the FCC exposure limits?
Answer The station licensee
Tip The station licensee is the one responsible for keeping everyone under the FCC exposure limits.
You Made It
Ten modules. All ten subelements, all 35 exam questions' worth of material, taught as a story instead of a flashcard deck.
Here is Ray's final speech, and it is short. "The test is 35 questions and you need 26. You are past ready. Book the exam session this week, before the details go stale. And the day your call sign shows up in the FCC database, do not celebrate by putting the radio on a shelf. Celebrate by keying up on 146.52 and finding out who is out there."
The license opens the door. Now go walk through it.
Next steps:
- Take two or three full practice exams. Miss a question, reread that module's section, not just the answer.
- Complete the Technician Skills Track and capstone from the curriculum page. Passing the exam makes you licensed. The skills make you ready.
- When 10 meters starts calling your name, the General course is waiting.
© 2026 Anthony Pelfanio, K4DIA. All rights reserved.
Review: every Exam Anchor from this module
T0A Shorting battery terminals: burns, fire, or explosion; rapid charge/discharge of unprotected batteries: overheating or out-gassing. Body current heats tissue, disrupts cells, and contracts muscles (all). Black wire = hot in 120 V cable. Fuse: removes power on overload; goes in series with the hot conductor only; never upsize (5 A to 20 A risks fire). Shock protection: three-wire cords, common safety ground, discharge high-voltage capacitors (all). After power-off, filter capacitors stay charged. Lightning arrester: grounded panel where feed lines enter. Bond all ground rods together. Use meters and leads rated for the voltage measured.
T0B Look for and stay clear of overhead power lines; never use utility poles; keep antennas far enough from lines that a falling antenna stays 10 feet away. Tower climbing: training, harness, and 100 percent tie-off (all); never climb without a helper; never climb a crank-up unless retracted or mechanically locked. Turnbuckle safety wire prevents vibration loosening. Ground each tower leg with its own eight-foot rod, all bonded together. Lightning ground connections: short and direct, avoiding sharp bends. Grounding requirements come from local electrical codes.
T0C RF is non-ionizing radiation; it lacks the energy to cause chemical changes and damage DNA. Touching a transmitting antenna: RF burn. Exposure limits vary with frequency because the body absorbs more at some frequencies; 50 MHz has the lowest MPE. Exposure depends on frequency and power, distance, and radiation pattern (all). Reduce exposure by relocating antennas. Duty cycle: percentage of time transmitting; it affects average exposure; 100 to 50 percent duty cycle doubles allowable power density. Evaluate by Bulletin 65 calculation, modeling, or calibrated measurement (all). Re-evaluate after any transmitter or antenna change. The station licensee is responsible.