Chapter 8Electrical and RF Safety

Basic Safety

• Have a master on/off switch for your station.

• Don’t work on “live” equipment. Check with a meter first.

• Discharge capacitors before working on equipment.

• Solder in a well ventilated area. Wash your hands after soldering to remove any lead and flux residue.– Some newer solders do not contain lead

Electrical Shock• Current is what is felt when shocked – but

it takes a high enough voltage to push that current through your skin and body.– Voltages as low as 30 volts can be dangerous

depending on your body’s resistance.– A current of more than a few milliamperes can

be dangerous.

Wiring and Safety Grounding• The National Electrical Code (NEC)

provides the information of how to safely handle AC wiring.

• Always use a 3-prong plug and ground the metal chassis or cabinet of equipment to ensure no hazardous voltages appear on the cabinet.

• A 20 A circuit requires 12 AWG wire.• A 15 A circuit requires 14 AWG wire.

Protective Equipment• Fuses break a circuit that is carrying an

excessive amount of current. Slow-blow fuses can handle some surges beyond their rated limit.

• Circuit breakers are like fuses, but are resettable.

• Never replace a fuse or circuit breaker with a larger value!

• Only place a fuse or circuit breaker on a hot wire – never on a neutral wire.– One exception: if you wire a radio directly to a battery

in a car you should put fuses on both the hot (+) and neutral (-).

• A safety interlock switch on equipment will de-energize the circuit whenever a cabinet is opened.

• A ground fault circuit interrupter (GFCI) senses a current imbalance of a few mA indicating an electrical shock hazard. The GFCI will break the circuit when this occurs.

Generator Safety• Never operate a generator in an enclosed

space. Always have adequate ventilation.

• Carbon Monoxide (CO) is in the exhaust of a gasoline or diesel generator. Install a CO detector if you use a generator regularly.

• A ground rod should be connected to the metal frame of a generator.

• If you connect the generator to your home you must have a transfer switch installed.

Lightning• The best protection is to disconnect all external

cables (antenna, rotator, etc.), unplug equipment power cords, and telephones.

• Surge protectors or DC ground on antennas will help prevent strikes by bleeding off charges.

• All towers and antenna mounts should be grounded.– Grounding wires should be short and direct.– Do not solder ground wires. Use mechanical clamps

or welds.– Lightning grounds should be bonded to other

grounds.

RF Exposure• Low lever RF exposure is not dangerous.

– Factors for exposure are power level, frequency, average exposure time, and transmission duty cycle.

• Heating of body tissue occurs when the body tissue absorbs the RF radiation. This is how a microwave oven works.

• RF radiation is non-ionizing, which means that the RF does not have enough energy to ionize (remove electrons) from material. Note, the energy of the RF is different from its power. The energy is the energy of one RF photon.

• The specific absorption rate (SAR) is the rate at which tissue absorbs the energy of the incident RF.

• SAR’s are greatest between 30 and 1500 MHz.

• Maximum Permissible Exposure (MPE) rates also vary with frequency.

• Time averaging is an average of the RF exposure over a fixed time interval.

• Controlled environments are where exposure to RF energy is controlled by access restriction or other measures.– The averaging period for controlled

environments is 6 minutes.

• Uncontrolled environments are areas with public access where people may not be aware of the RF exposure.– The averaging period of uncontrolled

environments is 30 minutes.

• Duty cycle is the ratio of time the transmitter is on to the total time.– If you listen half the time and transmit the

other half, then the duty cycle is 50%.– A lower transmission duty cycle permits

greater short term exposure for a given average exposure.

• Emission duty cycle is the average transmitter power during modulation.– SSB has an emission duty cycle of ~20%– FM has an emission duty cycle of 100%

• Average output power = Duty Cycle X Emission Duty Cycle X Transmitter PEP Power.– Example: A 100 W PEP SSB transmitter is

operated during a contest with a 50% duty cycle. What is the average output power?

• 100 x 20% x 50% = 10 W

• Antenna gain in the direction of the exposure area must be taken into account.

• All amateurs operating a fixed station must evaluate the RF exposure caused by their station.

• RF exposure must be measured only if transmitter power output exceeds the values given in Table 8-5 (p. 8-10).– RF exposure can be measured with a calibrated field

strength meter, or by using a table or online calculator (http://www.arrl.org/rf-exposure)

• If your evaluation of the RF exposure exceeds the MPE you can;– Locate the antenna further away from people. Fence

the area around the antenna.– Point beam antennas away from people.– Lower average transmit power.– Raise the antenna higher.– Indoor antennas should be evaluated to ensure that

MPE limits are not being exceeded.

Outdoor Safety• Never place antennas or feed lines near power

lines.• Before climbing a tower;

– Check tower guying and support hardware.– Crank-up towers must be fully collapsed.– Check all belts and lanyards.– Check ropes and pulleys (for pulling up antennas).– Turn off and secure all equipment. Lock the circuits if

possible.

• Use a climbing belt– Carabiners on climbing gear should be fully closed.– Latching hooks should close away from the tower.– Always use a safety lanyard or redundant lanyard.