Release 1.0 – September 2006 1 Electrical Safety Amateur radios operated at high power produce...

1Release 1.0 – September 2006

Electrical Safety

Amateur radios operated at high power produce dangerous and potentially deadly voltages and current. For example, it is commonly accepted that a voltages as low as 30 volts can cause a dangerous electric shock. It is very important to know how to work safely with electricity.


Lethal Current

There is a saying in electronics that “It’s the volts that jolts, but the mills that kills.”

As little as 100 milliamperes of electrical current flowing through the human body is likely to cause death. That’s only .1 amp, and this kind of current is very common in radio equipment!


Safe WiringYou may find

yourself installing or replacing an electrical outlet at some point. A typical modern outlet has three different wires, each with a different color. Each color must be connected correctly. Black wires go to the brass or gold terminals, white wires are connected to the silver terminals, and the bare or green wire is connected to the ground screw.


Fuses

Fuses are extremely important safety devices. The purpose of a fuse in an electrical circuit is to interrupt power in case of overload. This may happen if something inside the device “shorts” causing too much current to flow. Fuses are usually rated by the amount of current that will cause them to open or “blow.” A 10 amp fuse will open if 10 or more amps flow through the circuit it protects. When it opens, power to the unit is cut off.


Using the Right Size Fuse

You should always use a fuse of the correct size or rating. If you use a fuse rated for less current than that called for, the fuse will blow when the equipment is operating normally. If you use one that is rated for a higher current, it could cause enough current to flow through the device to do serious damage before the fuse opens. Worse yet, the heat generated could start a fire. For example, if you install a 20-ampere fuse in your transceiver in the place of a 5-ampere fuse, excessive current could cause a fire or burn up the transceiver circuitry.


Ways to Prevent Electrical Shock

There are several good ways to guard against electrical shock at your station. They include:

Using 3-wire cords and plugs for all AC powered equipment

Connecting all AC powered station equipment to a common ground

Using a ground-fault interrupter at each electrical outlet


Emergency Disconnect Switch

An emergency disconnect switch will quickly cut off all power to your station. This may be very important if something goes wrong while you are away from your operating position. For that reason, the most important thing to consider when installing an emergency disconnect switch at your station is that everyone should know where it is and how to use it. If others in your home don’t know where it is, they cannot turn it off in your absence.


Lightning StormsLightning storms can be extremely dangerous,

particularly to hams, because outdoor antennas make great lightning rods. If an antenna is hit by lightning, the electrical charge the lightning carries is headed straight for you and your station. When a lightning storm is expected, you should:

Disconnect the antenna cables from your station and move them away from your radio equipment

Unplug all power cords from AC outlets

Stop using your radio equipment and move to another room until the storm passes


Lightning and FireWithout a

doubt, the most important reason to have a lightning protection system for your amateur radio station is fire prevention.


Emergency Power

If you are able to use a 12 volt battery as a power source for your radio, one simple way to recharge the 12-volt battery if the commercial power is out is to connect the battery to a car's battery and run the engine.


Battery SafetyConventional 12-volt storage batteries are

widely available and often used by hams as an emergency power source. However, they must be handled carefully due to the potential hazards they pose. Hazards presented by conventional 12-volt storage batteries include:

They contain dangerous acid that can spill and cause injury if the case is broken.

Short circuits can damage wiring and possibly cause a fire

Explosive gas produced by such batteries can collect if not properly vented


Avoid Rapid Charge or Discharge of Storage Batteries

If a storage battery is charged or discharged too quickly, the battery could overheat and give off dangerous gas or explode. Most newer chargers are “smart” chargers that will prevent a too rapid charge. To prevent a battery from being discharged too quickly, you should use enough batteries in parallel to safely power your equipment.


CapacitorsYou will learn more about

capacitors when you study for your General class license. For now, however, you need to know that some types of capacitors, such as the electrolytic capacitors shown here, are capable of storing an electrical charge of hundreds of volts, and they can remain charged long after power is turned off. Devices such as power supplies have large capacitors that can hold dangerous charges. Even when a power supply is turned off and disconnected, you might receive an electric shock from a stored charge in these capacitors if you don’t know what your are doing. It’s not on the exam, but you should learn how to safely discharge these capacitors.


Check-Up Time!

Now let’s try the questions from this group.

You should make a note of any that you miss for later review.


T0A01

What is a commonly accepted value for the lowest voltage that can cause a dangerous electric shock?

A. 12 voltsB. 30 voltsC. 120 voltsD. 300 volts


T0A01 Answer - B

Thirty volts can be dangerous, although you can still get a nasty shock at voltages lower than this.


T0A02

What is the lowest amount of electrical current flowing through the human body that is likely to cause death?

A. 10 microamperes B. 100 milliamperesC. 10 amperesD. 100 amperes


T0A02 Answer - B

100 milliamperes or .1 amp is enough to kill. That doesn't sound like much, but bear in mind the old saying, "It's the volts that jolts, but the mils that kills!"


T0A03

What is connected to the green wire in a three-wire electrical plug?

A. Neutral

B. Hot

C. Ground

D. The white wire


T0A03 Answer - C

For safety, the green wire should always be connected to the ground terminal.


T0A04

What is the purpose of a fuse in an electrical circuit?

A. To make sure enough power reaches the circuit

B. To interrupt power in case of overload

C. To prevent television interference

D. To prevent shocks


T0A04 Answer - B

If a circuit suddenly begins to draw too much power, usually due to a component failure, the fuse "blows" breaking the connection between the device and the power source. Circuit breakers do the same thing, but unlike fuses, they can be reset and do not have to be replaced.


T0A05

What might happen if you install a 20-ampere fuse in your transceiver in the place of a 5-ampere fuse?

A. The larger fuse would better protect your transceiver from using too much current

B. The transceiver will run coolerC. Excessive current could cause a fire D. The transceiver would not be able to produce as much RF output


T0A05 Answer - C

Using a fuse larger than the value called for will allow more current to flow before it "blows." This could cause all kinds of damage, including allowing the transceiver to literally burn up, and could possibly start a fire as well.


T0A06

What is a good way to guard against electrical shock at your station?

A. Use 3-wire cords and plugs for all AC powered equipment

B. Connect all AC powered station equipment to a common ground

C. Use a ground-fault interrupter at each electrical outlet

D. All of these answers are correct


T0A06 Answer - D

All of these answers are good ways to protect yourself and your station from damage or injury. Hams often use equipment and components that develop high voltages and current. It is smart to play it safe!


T0A07

What is the most important thing to consider when installing an emergency disconnect switch at your station?

A. It must always be as near to the operator as possible

B. It must always be as far away from the operator as possible

C. Everyone should know where it is and how to use it

D. It should be installed in a metal box to prevent tampering


T0A07 Answer - C

An emergency disconnect allows you to "pull the plug" on all connected equipment instantly. Everyone in your home should know how to do this because you may not be around when it needs to be done.


T0A08

What precautions should be taken when a lightning storm is expected?

A. Disconnect the antenna cables from your station and move them away from your radio equipment

B. Unplug all power cords from AC outletsC. Stop using your radio equipment and move to another room until the storm passes



T0A08 Answer - D

All of these answers are correct. No good can come from a lightning bolt surging through your equipment. The easiest path for a lightning bolt to your radio is the outside antenna. Disconnect it. The next best path is through your home wiring, so you should always unplug your equipment and any other valuable appliances when a storm is approaching. Finally, if you are connected to your equipment when lightning strikes, need we say more?


T0A09

What is one way to recharge a 12-volt battery if the commercial power is out?

A. You cannot recharge a battery unless the power is back on

B. Add water to the battery C. Connect the battery to a car's battery and run the engine

D. Take your battery to the utility company for a recharge


T0A09 Answer - C

If your 12 volt battery is running low and the power is out, you can always recharge it using jumper cables from your car's battery.


T0A10

What kind of hazard is presented by a conventional 12-volt storage battery?

A. It contains dangerous acid that can spill and cause injury

B. Short circuits can damage wiring and possibly cause a fire

C. Explosive gas can collect if not properly vented



T0A10 Answer - D

All of these answers are correct. 12 volt batteries are great for emergency power, but they are somewhat dangerous. Dangers include acid spills, shorts, and unvented gasses.


T0A11

What can happen if a storage battery is charged or discharged too quickly?

A. The battery could overheat and give off dangerous gas or explode

B. The terminal voltage will oscillate rapidly

C. The warranty will be voidedD. The voltage will be reversed


T0A11 Answer - A

Charging or discharging a battery too quickly can cause overheating and possibly dangerous gas that could lead to an explosion. There are all kinds of "smart chargers" on the market today that will help you to avoid this very unpleasant result.


T0A12

What is the most important reason to have a lightning protection system for your amateur radio station?

A. Lower insurance ratesB. Improved receptionC. Fire preventionD. Noise reduction


T0A12 Answer - C

Nothing is more important than fire prevention. It doesn't matter how good your insurance happens to be. Some things simply cannot be replaced!


T0A13

What kind of hazard might exist in a power supply when it is turned off and disconnected?

A. Static electricity could damage the grounding system

B. Circulating currents inside the transformer might cause damage

C. The fuse might blow if you remove the cover

D. You might receive an electric shock from stored charge in large capacitors


T0A13 Answer - D

Power supplies rely on capacitors to produce smooth direct current at a steady voltage. These capacitors can store a hefty charge long after the supply has been turned off. Touching the leads of a charged capacitor can be very dangerous.


Group T0B

Group T0B covers antenna installation, tower safety, and overhead power lines.


Antenna Safety

Antenna safety goes hand in hand with electrical safety. Installing and maintaining an antenna can be dangerous if you don’t play it safe. For example, you should wear a hard hat and safety glasses if you are on the ground helping someone work on an antenna tower to protect your head and eyes in case something accidentally falls from the tower.


Climbing Safety

Another good idea before climbing an antenna tower is to put on a good climbing safety belt and safety glasses. One slip and it’s a long way down to the ground! In addition, you should arrange for a helper or observer on the ground, inspect the tower for damage or loose hardware, and above all, make sure there are no electrical storms nearby.


Picking a Site for Your Antenna

When you are transmitting, antennas can carry large high currents, so one very important consideration when putting up an antenna is to make sure people cannot accidentally come into contact with it. You don’t want someone getting a dangerous shock or RF burn.


Antennas and Airports

If you live close to an airport, you need to consult Part 97 to see whether you are close enough for height restrictions to be imposed on your antenna. (See § 97.15(A))


Keep Antennas Away From Power Lines!

The absolute most important safety precaution to observe when putting up an antenna tower is to look for and stay clear of any overhead electrical wires. If a falling antenna hits power lines, it can bring dangerous and damaging voltages into your station and could cause death by electrocution.


Safe Distance from Power Lines

A good rule of thumb for maintaining a safe distance to from a power line when installing an antenna is to install the antenna so that if it falls unexpectedly, no part of it can come closer than 10 feet to the power wires. That is an absolute minimum. Any less than that, and you are asking for trouble.


Tower Guy Wires

Most towers of any size need to have guy wires in place to secure the tower during high winds. The guy wires for an antenna tower should be installed strictly in accordance with the tower manufacturer's instructions. The engineers who designed the tower are in the best position to know how it should be done.


Crank-up TowersCrank-up towers are

towers made of nested sections that can be raised or lowered by means of a hand crank or electrical motor. However, these nested sections can fall, so the most important safety rule to remember when using a crank-up tower is that a crank-up tower should never be climbed unless it is in the fully lowered position. If you are on a higher section that gives way, you not only run the risk of falling. You may also run a very real risk of having a limb severed.


Preventing Antenna Corrosion

Stainless steel hardware is used on many antennas instead of other cheaper metals because stainless steel parts are much less likely to corrode than the cheap stuff. Corrosion not only damages the antennas. It also seriously affects your signal.


Towers Cannot Be Grounded Too Good!

Separate 8 foot long ground rods for each tower leg, bonded to the tower and each other is the minimum considered to be an adequate ground for a tower. A good earth ground improves the performance of many antennas. It also serves as the best path to ground for electrical energy from a lightning strike on your tower. It is better to see your tower destroyed than your home, and much better than you!


Check-Up Time!




T0B01

Why should you wear a hard hat and safety glasses if you are on the ground helping someone work on an antenna tower?

A. It is required by FCC rules B. To keep RF energy away from your head during antenna testing

C. To protect your head and eyes in case something accidentally falls from the tower

D. It is required by the electrical code


T0B01 Answer - C

This is a "well, duh!" question. You wear safety glasses and a hard hat to protect yourself!


T0B02

What is a good precaution to observe before climbing an antenna tower?

A. Turn on all radio transmittersB. Remove all tower grounding connections

C. Put on your safety belt and safety glasses

D. Inform the FAA and the FCC that you are working on a tower


T0B02 Answer - C

Here is another question with an obvious answer. When climbing a tower, you should wear a good pair of safety glasses and safety belt. The safety belt should be connected to the tower while you are working so that you will not fall if you slip or lose your balance.


T0B03

What should you do before you climb a tower?

A. Arrange for a helper or observer

B. Inspect the tower for damage or loose hardware

C. Make sure there are no electrical storms nearby



T0B03 Answer - D

Failing to do any one of these could be fatal. You do not want to become a "silent key" before your time. (Silent key is the term used for a ham that has passed on.)


T0B04

What is an important consideration when putting up an antenna?

A. Carefully tune it for a low SWRB. Make sure people cannot accidentally come into contact with it

C. Make sure you discard all packing material in a safe place

D. Make sure birds can see it so they don't fly into it


T0B04 Answer - B

The most important consideration in installing an antenna is to prevent others from coming in contact with it accidentally. While you are transmitting, the antenna is radiating power that can produce a significant shock hazard.


T0B05

What must be considered when erecting an antenna near an airport?

A. The maximum allowed height with regard to nearby airports

B. The possibility of interference to aircraft radios

C. The radiation angle of the signals it produces

D. The polarization of signal to be radiated


T0B05 Answer - A

§97.15(a)

(a) Owners of certain antenna structures more than 60.96 meters (200 feet) above ground level at the site or located near or at a public use airport must notify the Federal Aviation Administration and register with the Commission as required by Part 17 of this chapter.


T0B06

What is the most important safety precaution to observe when putting up an antenna tower?

A. Install steps on the tower for safe climbing

B. Insulate the base of the tower to avoid lightning strikes

C. Ground the base of the tower to prevent lightning strikes

D. Look for and stay clear of any overhead electrical wires


T0B06 Answer - D

Towers do occasionally fall. If your tower should fall, the last place you want it to land is on power lines.


T0B07

How should the guy wires for an antenna tower be installed?

A. So each guy wire anchor point has an even number of wires

B. So that no guy wire is more than 25 feet long

C. Each guy wire must be pulled as tight as possible

D. In accordance with the tower manufacturer's instructions


T0B07 Answer - D

Tower manufacturers do not want their towers to fall, so they take great pains to determine the best anchor points for guy wires. If you ever shell out big bucks for a good tower, follow the manufacturer's instructions.


T0B08

What is a safe distance from a power line to allow when installing an antenna?

A. Half the width of your property unless the wires are at least 23 feet high

B. 12.5 feet in most metropolitan areas C. 36 meters plus 1/2 wavelength at the operating frequency

D. So that if the antenna falls unexpectedly, no part of it can come closer than 10 feet to the power wires


T0B08 Answer - D

Here, the most reasonable answer is also the correct one. When you install a tower, insure that it will get no closer than 10 feet to the nearest power line if it falls.


T0B09

What is the most important safety rule to remember when using a crank-up tower?

A. This type of tower must never be paintedB. Crank up towers must be raised and lowered frequently to keep them properly lubricated

C. Winch cables must be specially rated for use on this type of tower

D. A crank-up tower should never be climbed unless it is in the fully lowered position


T0B09 Answer - D

Crank up towers, as the name implies, can be cranked up by allowing nested sections to be raised. That is a great way to get a tower up, but it should never be climbed when it is up. Always climb it when it is fully lowered. The upper sections do not always hold up very well with the weight of a person, and if they give way, a serious vertical drop will result!


T0B10

Why is stainless steel hardware used on many antennas instead of other metals?

A. Stainless steel is a better electrical conductor

B. Stainless steel weighs less than other metals

C. Stainless steel parts are much less likely to corrode

D. Stainless steel costs less than other metals


T0B10 Answer - C

Corrosion is the enemy of any antenna, and stainless steel is very resistant to corrosion.


T0B11

What is considered to be an adequate ground for a tower?

A. A single 4 foot ground rod, driven into the earth no more than 12 inches from the base

B. A screen of 120 radial wiresC. Separate 8 foot long ground rods for each tower leg, bonded to the tower and each other

D. A connection between the tower base and a cold water pipe


T0B11 Answer - C

The better the ground, the safer the tower. Separate 8 foot long ground rods for each tower leg, bonded to the tower and each other may sound like overkill, but it really is the bare minimum for safety.


Group T0C

Group T0C covers RF hazards, radiation exposure, and RF heating hazards. It also covers RF safety issues such as proximity to antennas, recognized safe power levels, hand held safety, and RF

exposure to others.


RF Safety

Radio waves, including VHF and UHF waves, are a type of “non-ionizing electromagnetic radiation.” These waves are all around us, and they generally do not pose any danger. However, excessive exposure to strong RF energy can be harmful to tissue. For that reason, the FCC has set RF exposure limits that all amateur stations must comply with.


RF Danger – Two Important Factors

Radio waves can cause injury to the human body only if the combination of signal strength and frequency cause excessive power to be absorbed by the body. So to determine the risk of harm from RF exposure, you must know both the signal strength and the frequency of the RF energy.


Why Frequency Matters

The frequency of an RF source must be considered when evaluating RF radiation exposure because the human body absorbs more RF energy at some frequencies than others. For example, the risk is somewhat higher at VHF frequencies than at HF frequencies.


Evaluating the Effects of RF Exposure

Several factors affect the RF exposure of people near an amateur transmitter, including:

Frequency and power level of the RF field – both must be considered.

Distance from the antenna to a person – the risk drops quickly as a person moves away from the antenna.

Radiation pattern of the antenna – this varies from one antenna to another. For example, a beam antenna has a stronger radiation pattern in the direction it is pointed, while a vertical antenna’s pattern is roughly the same in all directions.


When an RF Exposure Evaluation is RequiredIf an amateur station is putting out

less than a specified amount of power at a particular frequency, no exposure evaluation is required. For example, the maximum power level that an amateur radio station may use at frequencies above 30 MHz before an RF exposure evaluation is required is 50 watts PEP (peak envelope power) at the antenna. If the power level is less than 50 watts, no evaluation is required. (See §.13(C)(1))


How You Determine RF Safety Compliance

There are several ways you can determine that your station complies with FCC RF exposure regulations, including:

Calculating the risk based on FCC OET Bulletin 65 – this publication is available online or in print.

Calculating the risk using computer modeling – software is available that will let you “plug in the numbers” and calculate for your particular situation.

Measuring the field strength of your station using calibrated equipment.


RF Energy’s Affect on the Body

When RF energy penetrates the body it changes to heat energy. With a small amount of exposure, this is generally harmless. However, when the exposure is high, the heat produced can be significant enough to cause burns. For example, if a person were to accidentally touch your antenna while you are transmitting, they might receive a painful RF burn injury.


Reducing RF Radiation at Your Station

If you review your station and find that there is a risk of RF exposure greater than that allowed by the FCC, there are several actions you as an amateur operator can take to prevent exposure to RF radiation in excess of FCC supplied limits. They are:

Alter antenna patterns – the idea is to get the RF energy into the air where it can get your signal out without coming too close to people on the ground. A beam pointed away from the problem area might be one solution.

Relocate antennas – the greatest danger of RF exposure is near the antenna. Raising the antenna, moving it to the top of your home, or putting it in a different location on your property all might get it farther away from people.

Change station parameters such as frequency or power – if you can’t move the antenna or change its radiation pattern, you may be able to reduce power or move to bands that are within acceptable RF exposure limits.


Check-Up Time!




T0C01

What type of radiation are VHF and UHF radio signals?

A. Gamma radiation

B. Ionizing radiation

C. Alpha radiation

D. Non-ionizing radiation


T0C01 Answer - D

VHF and UHF radiation do not produce ions, so they are non-ionizing radiation. However, they can produce significant energy that can cause a shock and/or burn hazard.


T0C02

When can radio waves cause injury to the human body?

A. Only when the frequency is below 30 MHzB. Only if the combination of signal strength and frequency cause excessive power to be absorbed

C. Only when the frequency is greater than 30 MHz

D. Only when transmitter power exceeds 50 watts


T0C02 Answer - B

The signal strength required to produce injury depends on the frequency. It also depends on how close the person is to the radiator - the antenna.


T0C03

What is the maximum power level that an amateur radio station may use at frequencies above 30 MHz before an RF exposure evaluation is required?

A. 1500 watts PEP transmitter output

B. 1 watt forward power

C. 50 watts PEP at the antenna

D. 50 watts PEP reflected power


T0C03 Answer - C

§97.13(c)(1)

This subsection contains a table that specifies when an RF exposure evaluation is required. For all frequencies above 30 MHz, that level is 50 watts PEP.


T0C04

What factors affect the RF exposure of people near an amateur transmitter?

A. Frequency and power level of the RF field

B. Distance from the antenna to a person

C. Radiation pattern of the antennaD. All of these answers are correct


T0C04 Answer - D

All of these factors affect the potential RF exposure a person may be subject to.


T0C05

Why must the frequency of an RF source be considered when evaluating RF radiation exposure?

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 and do not affect the human body

D. The human body absorbs more RF energy at some frequencies than others


T0C05 Answer - D

The amount of energy absorbed by the human body is not the same at all frequencies, so frequency has to be considered in evaluating radiation exposure.


T0C06

How can you determine that 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 of these choices are correct


T0C06 Answer - D

§97.13(c)(1)

There are several ways to determine whether your station complies with FCC rules regarding RF exposure. All of the above can help you do so. The good news is that for the typical beginning Technician station, the analysis is not all that difficult.


T0C07

What could happen if a person accidentally touched your antenna while you were transmitting?

A. Touching the antenna could cause television interference

B. They might receive a painful RF burn injury

C. They would be able to hear what you are saying

D. Nothing


T0C07 Answer - B

Touching an antenna while someone is transmitting can lead to a nasty RF burn!


T0C08

What action might amateur operators take to prevent exposure to RF radiation in excess of FCC supplied limits?

A. Alter antenna patternsB. Relocate antennasC. Change station parameters such as frequency or power



T0C08 Answer - D

All of these answers are correct. The effect of all of these is to get the RF far enough away from humans not to pose a risk of danger.


T0C09

How can you make sure your station stays in compliance with RF safety regulations?

A. Compliance is not necessary B. By re-evaluating the station whenever an item of equipment is

changed C. By making sure your antennas have a low SWR

D. By installing a low pass filter


T0C09 Answer - B

When you install anything that changes your station's transmit characteristics, you need to redo the evaluation. A higher power transmitter, a new amplifier, a new or relocated antenna could all cause the RF exposure potential to change and should be evaluated.


T0C10

Which of the following units of measurement is used to measure RF radiation exposure?

A. Milliwatts per square centimeter

B. Megohms per square meter C. Microfarads per footD. Megahertz per second


T0C10 Answer - A

You want to know how much power is being exposed over a certain surface area. The only answer from these choices that gives you this information is milliwatts per square centimeter.


T0C11

Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?

A. It takes into account the amount of time the transmitter is operating

B. It takes into account the transmitter power supply rating

C. It takes into account the antenna feed line loss

D. It takes into account the thermal effects of the final amplifier


T0C11 Answer - A

"Duty cycle" is a description of how much time the transmitter is actually transmitting, and therefore actually radiating RF. The duty cycle depends on the mode you are using.


You Did It!Now Go Out There And Ace That

Test!

This concludes Study Guide # 10.

Once you are satisfied that you can answer 80% of the questions in this Sub-element, you

are ready to take your Technician exam!

Release 1.0 – September 2006 1 Electrical Safety Amateur radios operated at high power produce...

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