Electrical and antenna safety

This guide covers the hazards around an amateur station: household AC power, the energy stored in batteries and power supplies, lightning, and the height and power lines involved in putting up antennas. RF exposure has its own rules and its own guide.

How electric shock harms you

What injures you is current flowing through your body. OSHA lists four factors that set the severity: the amount of current, its path through the body, how long it flows, and its frequency (OSHA 3075). OSHA’s table for current flowing hand to foot for one second:

A milliampere (mA) is one thousandth of an ampere (NIST). OSHA calls burns the most common shock-related injury, and an involuntary muscle reaction to a shock can cause a fall, for example from a ladder. Dry skin resists current, but wet skin conducts, so damp locations need extra care (OSHA 3075).

Fuses, breakers and GFCIs

Fuses and circuit breakers open the circuit when too much current flows. They exist to protect the wiring and equipment from overheating (OSHA 3075). That is why you must never replace a fuse with a higher-rated one: a 20 A fuse where a 5 A fuse belongs lets excessive current flow, which can cause a fire (Technician pool, T0A05). Replace a fuse with the same rating, and if it keeps blowing, find the fault.

In a 120 V AC circuit, the fuse or circuit breaker goes in series with the hot conductor only (Technician pool, T0A08). In a 240 V circuit, only the hot wires are fused (General pool, G0B01). OSHA describes the usual US color code: equipment grounding conductors are green or green with a yellow stripe, grounded (neutral) conductors are white or gray, and hot wires are often black or red (OSHA 3075).

A ground-fault circuit interrupter (GFCI) compares the current going out with the current coming back. If they differ by more than 5 mA, meaning some current is leaking through a person or other path, it cuts the power in as little as 1/40 of a second. OSHA notes that GFCIs are used in wet locations, construction sites and other high-risk areas (OSHA 3075), so use GFCI protection outdoors and in damp places such as basements and portable operating sites.

Inside equipment, the danger can outlast the off switch. Charge stored in a power supply’s filter capacitors is a hazard right after the supply is turned off (Technician pool, T0A11), and a power supply interlock exists to remove dangerous voltages when the cabinet is opened (General pool, G0B12). When you measure high voltage, use a voltmeter and test leads rated for that voltage (Technician pool, T0A12).

Grounding and bonding

Station grounding serves three separate purposes, according to the ARRL: AC electrical safety, control of stray RF, and lightning protection (ARRL). They have different requirements:

• Safety ground: the equipment grounding conductor in your AC wiring. It gives current a second path to ground if a fault energizes a metal case, and that current may trip the circuit protection. OSHA notes that grounding substantially reduces the risk of shock but does not guarantee against it (OSHA 3075). Its requirements come from your state and local electrical codes (ARRL; Technician pool, T0B11), and the National Electrical Code covers the electrical safety of a station (General pool, G0B06).
• Lightning ground: the ARRL calls these requirements “much more stringent than for a safety ground”, since “a lot of energy must be safely dissipated” (ARRL).
• RF ground: required only for antennas that need current flow to ground to complete the antenna circuit, such as a quarter-wave vertical (ARRL).

Bonding means connecting these grounds together. Lightning protection ground rods must be bonded together with all other grounds (General pool, G0B11), using heavy wire or conductive strap (Technician pool, T0A09). Keep lightning ground connections short and direct, and avoid sharp bends (Technician pool, T0B01 and T0B10). The ARRL’s book on the subject describes a single-point ground panel (SPGP) with surge protectors mounted on it (ARRL), and lightning arrestors belong on a grounded panel near where feed lines enter the building (Technician pool, T0A07).

Lightning

The National Weather Service says there is no safe place outside when thunderstorms are in the area. Once indoors, do not touch anything plugged into an electrical outlet, plumbing or corded phones, and wait 30 minutes after the last lightning or thunder before going back out (NWS). Operating a station means touching plugged-in equipment, so do not operate while a storm is nearby. For your station:

• If you disconnect feed lines and unplug equipment, do it before a storm arrives. Once it is near, the NWS advice is not to touch anything plugged in.
• Install lightning arrestors where the feed lines enter the building (General pool, G0B13).
• Locate the lightning protection ground system outside the building (General pool, G0B04) and bond it to all other grounds, including the electrical service ground (General pool, G0B11).

Batteries

Shorting the terminals of a 12 V storage battery that lacks internal protection circuitry, for example with a wrench or a ring, can cause burns, fire or an explosion (Technician pool, T0A01). Unsealed batteries give off gases, and OSHA requires ventilation in workplaces “to prevent the accumulation of an explosive mixture” (29 CFR 1926.441). Charging or discharging an unprotected battery too fast can make it overheat or give off gas (Technician pool, T0A10).

Lithium-ion batteries combine a flammable electrolyte with a lot of stored energy, and a damaged cell can go into thermal runaway, a chain reaction in which heat from one failing cell damages the next (OSHA 4480). OSHA’s advice (SHIB 06-20-2019):

• Use batteries and chargers tested to a recognized standard and approved for your device, and follow the manufacturer’s charging instructions.
• Avoid dropping, crushing or puncturing them. Damage can occur above about 130°F, and charging a lithium-ion battery below freezing (32°F) can cause lasting internal damage.
• Remove batteries from the charger when they are full, and store them somewhere cool and dry.
• Stop using any battery that bulges, cracks, hisses, leaks, gets hot or smokes. Move it away from anything flammable; OSHA suggests a fire-resistant container such as a metal drum with sand.

Towers, masts and power lines

Plan the installation so that if the antenna falls, no part of it can come within 10 feet of the power wires (Technician pool, T0B06). If a tower or mast starts to fall, get away from it. If someone becomes energized, do not touch them; use an insulated wooden pole to knock the energized conductor away, then call for emergency help (ARRL).

OSHA lists the main hazards of tower work as falls, electrical hazards, falling objects, weather, equipment failure and structural collapse (OSHA). For amateur towers:

• Use a tower designed and installed to engineering specifications, check with your local building officials, and keep children from climbing it (ARRL).
• The assembly crew and climbers wear hard hats and protective equipment including gloves, boots, a climbing belt and a harness, and use a lifeline whenever the belt is unattached while moving (ARRL). Confirm that the harness is rated for your weight and within its allowable service life (General pool, G0B07).
• Climb only with training in safe climbing techniques, an approved climbing harness, and appropriate tie-off to the tower at all times (Technician pool, T0B02).
• Never climb without a helper or observer (Technician pool, T0B03).
• Before climbing a tower that supports powered equipment, such as a rotator, make sure all circuits that supply power to the tower are locked out and tagged (General pool, G0B08).
• Never climb a crank-up tower unless it is retracted or mechanical safety locking devices have been installed (Technician pool, T0B07).
• Ground a tower with a separate eight-foot ground rod for each leg, bonded to the tower and to each other (Technician pool, T0B08).