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Amateur Radio Info & Exams - Safety - RF and Electrical Safety

This is the final, and most important page.

RF Safety

Intense RF fields can cause heating of body tissue, but beyond this, there is no evidence that RF causes injury, remembering that this is non-ionising radiation. There are however speculative exposure limits. The basic one is the actual signal density, driven by power and antenna gain. The permitted level varies with frequency, being most strict in the VHF bands. Also, duty cycle comes into play, such as the typical 50% transmit time during a conversation.

At sensible power levels, such as 100 watts into a dipole at HF, the level is safe at the distance of 2.5 metres you need to have to prevent someone touching the antenna. For ground mounted antennas, typically used at low HF, such as 80 metres, a timber fence or plastic mesh barrier is needed, primarily to prevent touching, but also to comply with EMR rules.

A high gain, directional antenna, especially on VHF or UHF is where you may generate high field strengths, and the exam indicates you need to prevent the antenna pointing in the direction of a house where you would exceed this level. (A mark on the dial of a rotator control is probably sufficient). However, reducing power in that direction is also an option.

Power safety

US power connections

US power, in most cases, consists of a a split phase connections, where the single phase is centre-tapped, so the 240 volts is grounded at the centre, and this point is also the neutral. Thus small items like supplies for 12 volt rigs, HT chargers, most lamps, and computers are connected from a single hot to neutral, a 120 volt supply. Heavy duty devices, such as large linear amplifiers and heating equipment is connected between the hots, although control circuits and fans can be powered from a hot-to-ground (120 volt) connection. Thus in these cases a 4 wire connection is used, the two hots, the neutral, and the safety ground (earth). The US system has a vast number of different plugs, for different configurations and currents of supply.

If you are setting up a dedicated area at home for a "shack" you might consider having some dedicated outlets installed, on their own circuit(s). Commercial grade, brand name, outlets are not much more costly. If you are using a large amplifier, a dedicated high current 120 volts outlet (NEMA 5-20R), or 240 volt outlet (NEMA 6-15R), should power it. Or, NEMA 14-15R and similar outlets have both hots (240 volts) and the neutral, so components of both 120 and 240 volts can be used within the amplifier.

Also, avoid any sort of USB power supply in the outlet. I have a feeling they generate plenty of electrical noise and radio interference, and you can't unplug them if they do!

Plugs should also be good quality, brand name items with a NEMA marking, such as "MEMA 5-15P".


In these connections, the two hots must be fused, but not the neutral, nor the earth.


"Ground fault circuit interrupter (GFCI)" is American for "residual-current device (RCD)" or "residual-current circuit breaker (RCCB)", or "safety switch" for Australian consumers. The technically descriptive name is the earth leakage core balance relay (ELCBR).

In these current carrying conductors pass through a small toroid. A winding on this toroid feeds a simple amplifier which triggers a breaker to remove power if the current is unbalanced.

Single phase, two wire ones (US 120 volt or Aussie 240 volt) ones work by comparing the current in the active with that in the neutral, and if there is a difference, this means current is flowing directly to ground, possibly via a person's body. For split phase with no neutral (US 240 volts) the current must be equal in both hots, or the device will trip. Even with a Neutral in the 240 volt system with, say a 10 amp load between hots, and a 1 amp load from hot to neutral the current in the 3 wires going through the core balances.

Note that very old voltage-operated earth leakage circuit breaker (ELCB) only detect current flowing from the equipment chassis back to the switchboard via the earth wire. Thus, current flowing to ground elsewhere will not trip the device.

The two big risks these do not protect against are: Contact between Active and Neutral, between two Actives in a 3 phase system, or between the two Hots of a US domestic 240 volt system. The second is contact with dangerous AC or DC voltages beyond a transformer, such as in a valve / tube device.

Wire gauge

Instead of wire size using square millimetres, the US uses American Wire Gauge, with large sizes being 0, or several zeros, and increases, normally by 2, which indicates smaller sizes, with very fine "magnet" or coil-winding wire having the largest numbers. Numbers between 8 to 16 relate mains wiring at home, 4 to 8 might be useful for DC wiring of transceivers. For mains power the primary consideration tends to be not having the wire overheat, and damage the insulation, or cause a fire. The wire size and fusing are linked. Factors, such as in ceiling insulation over wiring, or confining multiple conductors within a conduit or duct make de-rating necessary.

AWG number 14 wire needs to be fused at 15 amps, according to the examiner. If this load was carries constantly, the wire would experience a fair degree of warming, especially if there is no airflow around it, or it is in a hot roof space. To carry 20 amps no. 12 wire is required.

The said examiner however fails to mention that this only applies to copper wire. The US has a history of fitting aluminium (or "aluminum") wire in houses and commercial premises. Its higher resistivity means a greater cross-sectional area (lower AWG number) is needed for a certain current. Specialised termination methods are required to prevent fires. This is because aluminium's expansion and contraction can loosen screw clamps, and because the oxide layer can increase resistance, these are subject to overheating joints, which can cause fires, with one example killing 165 people, and injuring over 200 more. Specially certified electricians must fit approved crimped transitions to copper pigtails, or use other approved techniques. Purple wire-nuts are only for temporary repairs.

Most other countries specify wire in square millimetres. Examples of "building wire" are 1, 1,5, 2.5, 4, 6, and 10 mm². Flex includes 0.75, 1.0, 1.5, and 2.5 mm². In both cases there are large cables for industrial uses.

A bit off topic, but useful, for 12 volt systems we are normally selecting conductors for low voltage drop, so the conductor is often thicker than needed for safety. You might fuse the beginning of the cable for its protection, maybe 35 amps, then at the other end, fuse for the radio (maybe 20 or 25 amps). There is discussion about fusing the negative run to the radio, and whether this connection should be to the body end of the grounding strap, or on the battery. A 45 amp fuse in the negative may be useful, especially if connecting to the battery negative, in case the negative strap comes lose, and the starting current attempts to flow via your radio wiring, and the antenna base.


For field day events, or after disasters, it may be necessary to run station equipment from a small petrol (gasoline), or other generator. The exam focuses on the carbon-monoxide (CO) hazard from these. CO is an odourless, toxic gas which interferes with your blood carrying oxygen to your organs, with symptoms similar to a cold or influenza, minus the throat pain. Thus generators must be placed in areas which are well ventilated. An earth stake to the frame is a good idea. You may want to have it some distance from the station, to limit the audio and electrical noise from the generator. Especially at 120 volts, you may want to use a cable heavier than strictly necessary, to reduce the voltage drop.

These will eventually be banned in California, and while the goal may be something like a large, higher voltage lithium battery pack running an inverter, and charged by high voltage solar panels, the regulation does not ban diesel (compression ignition) engines, so that is probably where things will end up.

If you connect a generator to your house, you must either have interlocked breakers, or otherwise disconnect the incoming connection, to ensure this power cannot go into the street wiring, so you don't "Electrolux" the line workers. A cable to your 'fridge and freezer, a few lights, and plug-in cooking equipment, connected when needed, may be a safer option, as long as it is not a trip hazard.


The NEC is the National Electrical Code, and various versions have been ratified at the state or county level, making them the regulations applying to domestic and commercial power installations, including Amateur Radio shacks. Portable buildings, travel trailers, caravans, RVs, and (presumably) communications vans also need to comply.

The NEC is written by the National Fire Protection Association.

Test Gear

Multimeters, and the like must be used with care on mains, or other voltages above around 45 volts; and with high current circuits, or high current capability, such as larger batteries. This includes following voltage ratings and meter classes.

Current transformers, as used in some tong testers, and fixed installations are capable of developing lethal voltages across their terminals if these are not correctly terminated. If it steps current down, there is the potential for it to step voltage up.

Relevant Questions

These are actual questions from the General exam pool.

What is one way that RF energy can affect human body tissue?
A. It heats body tissue
B. It causes radiation poisoning
C. It causes the blood count to reach a dangerously low level
D. It cools body tissue

It causes heating of body tissue, just as a microwave heats food, answer A.

Which of the following properties is important in estimating whether an RF signal exceeds the maximum permissible exposure (MPE)?
A. Its duty cycle
B. Its frequency
C. Its power density
D. All of these choices are correct

It is all these factors, answer D.

G0A03 [97.13(c)(1)]
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

Each of these are options, answer D.

What does "time averaging" mean in reference to RF radiation exposure?
A. The average amount of power developed by the transmitter over a specific 24 hour period
B. The average time it takes RF radiation to have any long-term effect on the body
C. The total time of the exposure
D. The total RF exposure averaged over a certain time

This is ability to average RF exposure over a period, such as 6 minutes, answer D.

What must you do if an evaluation of your station shows RF energy radiated from your station exceeds permissible limits?
A. Take action to prevent human exposure to the excessive RF fields
B. File an Environmental Impact Statement (EIS-97) with the FCC
C. Secure written permission from your neighbors to operate above the controlled MPE limits
D. All of these choices are correct

You need to take action to prevent exposure at excessive levels, such as raising the antenna, answer A.

You can also reduce power when transmitting in that direction, or move the antenna away from the boundary.

What precaution should be taken when installing a ground-mounted antenna?
A. It should not be installed higher than you can reach
B. It should not be installed in a wet area
C. It should limited to 10 feet in height
D. It should be installed such that it is protected against unauthorized access

They should be installed so it is not possible to easily access the antenna, answer D. A non-metallic fence is one option.

What effect does transmitter duty cycle have when evaluating RF exposure?
A. A lower transmitter duty cycle permits greater short-term exposure levels
B. A higher transmitter duty cycle permits greater short-term exposure levels
C. Low duty cycle transmitters are exempt from RF exposure evaluation requirements
D. High duty cycle transmitters are exempt from RF exposure requirements

A low duty cycle means that the short-term power can be higher, answer A. If 500 watts was OK, but you operate mainly on an a net with 4 members, so only transmit one minute in four, the limiting factor becomes 1500 watts legal power, below the 2 kW this calculation gives.

Which of the following steps must an amateur operator take to ensure compliance with RF safety regulations when transmitter power exceeds levels specified in FCC Part 97.13?
A. Post a copy of FCC Part 97.13 in the station
B. Post a copy of OET Bulletin 65 in the station
C. Perform a routine RF exposure evaluation
D. All of these choices are correct

You must perform the routine RF exposure valuation, answer C.

For stations running 100 watts on HF, or similar power on VHF into a small yagi, this may well comply as long as antennas are beyond touching distance (2.5 metres) from the fenceline.

What type of instrument can be used to accurately measure an RF field?
A. A receiver with an S meter
B. A calibrated field strength meter with a calibrated antenna
C. An SWR meter with a peak-reading function
D. An oscilloscope with a high-stability crystal marker generator

This is the calibrated meter with a calibrated antenna, answer B.

Just link "accurate" and "calibrated" in your mind.

What is one thing that can be done if evaluation shows that a neighbor might receive more than the allowable limit of RF exposure from the main lobe of a directional antenna?
A. Change to a non-polarized antenna with higher gain
B. Post a warning sign that is clearly visible to the neighbor
C. Use an antenna with a higher front-to-back ratio
D. Take precautions to ensure that the antenna cannot be pointed in their direction

You need to make sure you don't point antenna in their direction if operating at full power, answer D.

What precaution should you take if you install an indoor transmitting antenna?
A. Locate the antenna close to your operating position to minimize feed line radiation
B. Position the antenna along the edge of a wall to reduce parasitic radiation
C. Make sure that MPE limits are not exceeded in occupied areas
D. Make sure the antenna is properly shielded

You need to make sure limits are not exceeded in an occupied area, answer C.

Which wire or wires in a four-conductor connection should be attached to fuses or circuit breakers in a device operated from a 240 VAC single phase source?
A. Only the two wires carrying voltage
B. Only the neutral wire
C. Only the ground wire
D. All wires

Remember that this is the US "split phase" system, used for large loads, and the two "hot" or voltage carrying lines should be fused. The neutral should not be fused, and most definitely NOT the ground or earth. Answer A.

According the National Electrical Code, what is the minimum wire size that may be used safely for wiring with a 20 ampere circuit breaker?
A. AWG number 20
B. AWG number 16
C. AWG number 12
D. AWG number 8

This is AWG number 12 wire, answer C.

This is a respectable 3.31 mm².

Which size of fuse or circuit breaker would be appropriate to use with a circuit that uses AWG number 14 wiring?
A. 100 amperes
B. 60 amperes
C. 30 amperes
D. 15 amperes

No 14 is only suitable for 15 amps, answer D.

The is 2.08 mm². In both cases these sizes exceed the requirements in Australia for use at

Which of the following is a primary reason for not placing a gasoline-fueled generator inside an occupied area?
A. Danger of carbon monoxide poisoning
B. Danger of engine over torque
C. Lack of oxygen for adequate combustion
D. Lack of nitrogen for adequate combustion

Generators, like all small gasoline (petrol) engines, produce significant amounts of toxic (and odourless) carbon monoxide, in addition to carbon dioxide, oxides of nitrogen, partially burnt fuel, and particulates.

California will ban new petrol lawn equipment, chainsaws, and golf carts by 2024, and new petrol generators by 2028, with use to end in 2035.

Which of the following conditions will cause a Ground Fault Circuit Interrupter (GFCI) to disconnect the 120 or 240 Volt AC line power to a device?
A. Current flowing from one or more of the voltage-carrying wires to the neutral wire
B. Current flowing from one or more of the voltage-carrying wires directly to ground
C. Overvoltage on the voltage-carrying wires
D. All of these choices are correct

These are called RCDs (residual current devices), ELCBRs (Earth Leakage Core Balance Relays), or Safety Switches, and detect when current is flowing to earth, and disconnect the power in a fraction of a second, answer B.

Which of the following is covered by the National Electrical Code?
A. Acceptable bandwidth limits
B. Acceptable modulation limits
C. Electrical safety inside the ham shack
D. RF exposure limits of the human body

This is the electrical safety standard which applies to pretty much any place a ham shack can be, including homes, residential care centres, schools, community centres, emergency operations centres, and to mains voltage wiring in RVs, answer C.

Hams in other countries must comply with the standards in their countries, such as the AS/NZS 3000 series Downunder.

Which of these choices should be observed when climbing a tower using a safety belt or harness?
A. Never lean back and rely on the belt alone to support your weight
B. Confirm that the belt is rated for the weight of the climber and that it is within its allowable service life
C. Ensure that all heavy tools are securely fastened to the belt D-ring
D. All of these choices are correct

Ensure that the belt is correctly rated, and in date, answer B.

That said, appropriate measures should be taken to avoid tools falling.

What should be done by any person preparing to climb a tower that supports electrically powered devices?
A. Notify the electric company that a person will be working on the tower
B. Make sure all circuits that supply power to the tower are locked out and tagged
C. Unground the base of the tower
D. All of these choices are correct

Breakers for electrical equipment on the tower must be locked out, and tagged. This might be microwave gear, and lighting. Answer B.

Disabling daytime strobes may require notification to the FAA, ahead of work.

Which of the following is true of an emergency generator installation?
A. The generator should be located in a well-ventilated area
B. The generator must be insulated from ground
C. Fuel should be stored near the generator for rapid refueling in case of an emergency
D. All of these choices are correct

Due to carbon monoxide, and other toxic exhaust components, these must be located in a well ventilated area, answer A.

When generators are installed in buildings, properly engineered exhaust and cooling systems are required.

Which of the following is a danger from lead-tin solder?
A. Lead can contaminate food if hands are not washed carefully after handling the solder
B. High voltages can cause lead-tin solder to disintegrate suddenly
C. Tin in the solder can "cold flow" causing shorts in the circuit
D. RF energy can convert the lead into a poisonous gas

Lead is toxic, and if you don't carefully wash your hands (including thumbs) after soldering, you can contaminate food, answer A.

Cold-flow is really only a problem with near pure tin, and joint failure due to extreme currents (lighting, serious mains faults) relates to any soldered joint.

Which of the following is good practice for lightning protection grounds?
A. They must be bonded to all buried water and gas lines
B. Bends in ground wires must be made as close as possible to a right angle
C. Lightning grounds must be connected to all ungrounded wiring
D. They must be bonded together with all other grounds

The lightning ground must be bonded to other grounds, such as power earth, answer D.

Cabling should be as straight as possible, or use gentle curves.

What is the purpose of a power supply interlock?
A. To prevent unauthorized changes to the circuit that would void the manufacturer’s warranty
B. To shut down the unit if it becomes too hot
C. To ensure that dangerous voltages are removed if the cabinet is opened
D. To shut off the power supply if too much voltage is produced

These either cut-off, or short dangerous voltages to ground (blowing the fuse) to ensure these are not present when the cabinet is open, answer C.

The correct procedure is to remove power, and wait a period for the capacitors to discharge, then open the cabinet, and to check using a meter with a suitable High Voltage probe.

What must you do when powering your house from an emergency generator?
A. Disconnect the incoming utility power feed
B. Insure that the generator is not grounded
C. Insure that all lightning grounds are disconnected
D. All of these choices are correct

You need to disconnect the incoming mains power supply, answer A.

This prevents you electrocuting lines workers.

What precaution should you take whenever you adjust or repair an antenna?
A. Ensure that you and the antenna structure are grounded
B. Turn off the transmitter and disconnect the feed line
C. Wear a radiation badge
D. All these choices are correct

You need to ensure RF energy can't be transmitted to the antenna, answer B.

CONGRATULATIONS! You have now reviewed all questions.

I would suggest doing some drills on hamtestonline.com, which are available without charge.

It is also time to look at Exams.

You can also continue to the Extra paper, starting at Regulations 1.

You can find links to lots more on the Learning Material page.

This has taken a fair bit of work to write, so if you have found this useful, there is a "tip jar" below.

You may also want to get a Ham related shirt, sticker, mug, etc, designed by your author: VK-73

Written by Julian Sortland, VK2YJS & AG6LE, April 2022.

Tip Jar: a Jefferson (US$2), A$3 or other amount / currency. Thanks!