Electrical safety
BE SAFE!
When operating or working on amateur radio equipment, it’s possible to come into contact with dangerous voltages and currents. People have died working on high-voltage circuits. Because it would be a shame to lose a single person, it’s important to know how to be safe when working with electricity.
30 volts is the commonly accepted value for the lowest voltage that can cause a dangerous electric shock, and only 100 mA flowing through the body can cause death. These are not very large values.
T0A02
What health hazard is presented by electrical current flowing through the body?
A. It may cause injury by heating tissue
B. It may disrupt the electrical functions of cells
C. It may cause involuntary muscle contractions
D. All these choices are correct
Start by ensuring that your amateur radio station has three-wire electrical outlets that are properly wired and grounded. When properly wired, three-wire electrical outlets and plugs are safer than two-wire outlets and plugs, and you should use three-wire plugs for all of your amateur radio equipment. In the United States, the three wires are hot, neutral, and safety ground, These are color-coded black, white, and green, respectively. In addition to ensuring that all AC outlets are properly wired, install mechanical interlocks in high-voltage circuits that disconnect power when equipment enclosures that contain those circuits are opened.
T0A03
In the United States, what circuit does black wire insulation indicate in a three-wire 120 V cable?
A. Neutral
B. Hot
C. Equipment ground
D. Black insulation is never used
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. Install mechanical interlocks in high-voltage circuits
D. All these choices are correct
Installing fuses in an electrical circuit is the main way to protect a circuit from excessive current flow, or overload. Fuses are designed to “blow” or remove power from equipment if the current flowing through them exceeds a specified value. Fuses should always be in series with the hot conductor only.
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 overload
C. To limit current to prevent shocks
D. All these choices are correct
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
When replacing a fuse, always replace the blown fuse with a fuse of the same type and value. Using a fuse with a larger current rating may allow excessive current to flow in the circuit and cause it to catch fire.
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. All these choices are correct
Whenever you’re working on equipment, be sure to disconnect it from the power lines, and even then be careful when working near a power supply’s capacitors. Some power supplies have large capacitors in their output circuits that can store a lot of charge, and if you come into contact with them before they are discharged, you may receive an electrical shock. I always measure a power supply’s output voltage before working on it or connecting or disconnecting equipment to the supply.
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
You also need to take precautions when using batteries to power your amateur radio station. Conventional 12-volt storage batteries present several safety hazards.
T0A01
Which of the following is a safety hazard of a 12-volt storage battery?
A. Touching both terminals with the 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
T0A10
What hazard is caused by charging or discharging a battery too quickly?
A. Overheating or out-gassing
B. Excess output ripple
C. Half-wave rectification
D. Inverse memory effect
Antenna and tower safety
Antenna safety is also of primary concern. There are two aspects of antenna safety—being safe when installing an antenna and safely operating an antenna. When installing an antenna, make sure you note where the power lines are and position the antenna, so that if it falls, no part of it comes closer than 10 feet to the power wires.
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
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 closer than 10 feet to the power wires
And, you should NEVER attach an antenna to a utility pole because it could contact high-voltage power lines.
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 60 Hz radiations from the feed line may increase the SWR
C. The antenna could contact high-voltage power lines
D. All these choices are correct
You also should position the antenna so that no one can touch it while you are transmitting.
T0C07
What hazard is created by touching an antenna during a transmission?
A. Electrocution
B. RF burn to skin
C. Radiation poisoning
D. All these choices are correct
There are a number of things you should keep in mind when putting up a tower and installing antennas on them.
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
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
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
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
Grounding is very important when installing a tower. The tower is, after all, basically a big lightning rod. Proper grounding will help shunt a lightning strike to earth before it can get into your amateur radio station.
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
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
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
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
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
Lightning can also be conducted down a feed line and into your station. To prevent this, several manufacturers make devices called lightning arrestors that are designed to conduct this current to ground before it gets into the station. Mount lightning arrestors on a grounded panel near where feed lines enter a building.
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
RF hazards and radiation exposure
Even though radio waves are non-ionizing radiation, over-exposure to RF energy can be a safety hazard.
T0C01
What type of radiation are radio signals?
A. Gamma radiation
B. Ionizing radiation
C. Alpha radiation
D. Non-ionizing radiation
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
To ensure that your amateur radio station is operating safely, the FCC has set exposure limits. As an amateur radio station licensee, you are responsible for ensuring that no person is exposed to RF energy above these limits. There are three ways to determine whether your station complies with FCC RF exposure regulations:
- By calculation based on FCC OET Bulletin 65
- By calculation based on computer modeling
- By measurement of field strength using calibrated equipment
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
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
One of the factors to consider when performing an RF exposure evaluation is duty cycle. Duty cycle is defined as the percentage of time that a transmitter is transmitting. Duty cycle is important because it affects a person’s average exposure to RF radiation. A transmission with a lower duty cycle would be less hazardous than a high duty cycle transmission.
T0C11
What is the definition of duty cycle during the averaging time for RF exposure?
A. The difference between the lowest power output and the highest power output of a transmitter
B. The difference between the PEP and 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
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
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
Because of the way radio waves interact with the body, the exposure limits are different for each amateur radio band. Oddly, 50 MHz is the frequency at which the human body absorbs the most radiation. In addition to the frequency and power level of the RF field, the distance from an amateur station antenna and radiation pattern of the antenna affect how much RF exposure that people will experience near the antenna.
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
T0C02
At which of the following frequencies does maximum permissible exposure have the lowest value?
A. 3.5 MHz
B. 50 MHz
C. 440 MHz
D. 1296 MHz
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
So, what should you do if your RF exposure evaluation shows that people are being exposed to excessive RF?
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
You could also lower the power or simply transmit less.
Finally, you should regularly evaluate your station for RF safety.
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. All these choices are correct
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