This group covers the electrical hazards in a ham shack: shock from household and high-voltage circuits, protective devices such as fuses and breakers, grounding, lightning protection, and the dangers of storage batteries. Most of it is common sense backed by a few firm rules.
How electricity hurts you
Current flowing through the body is what causes harm. It can heat tissue and cause burns, disrupt the electrical signals that run your nerves, heart and cells, and force muscles to contract so you cannot let go of the conductor. All of these effects are real, so treat any energized circuit with respect.
AC wiring colors and fusing
In the US, a three-wire 120 V AC cable uses black for the hot conductor, white for neutral, and green or bare copper for the equipment (safety) ground. Treat black as live.
Fuses and circuit breakers protect against overload. They must be placed in series with the hot conductor only, so the dangerous side of the circuit is opened. Never replace a fuse with a larger rating: a 20 A fuse in a 5 A circuit lets four times the design current flow, and wiring or equipment can overheat and start a fire before it blows. A fuse protects the weakest part of the circuit, not you from shock.
Shock-prevention habits
- Use three-wire cords and plugs on all AC powered equipment.
- Connect all station equipment to a common safety ground.
- Fully discharge large high-voltage capacitors before working inside equipment. Filter capacitors in a power supply can hold a lethal charge long after the supply is switched off, so check them with a meter.
- When measuring high voltage, use a voltmeter and test leads rated for at least the voltage being measured.
Lightning protection and grounding
A lightning arrester (surge protector) on a coax feed line should be mounted on a grounded panel where the feed lines enter the building. That diverts surge current to the outside ground system before it reaches your equipment. All external ground rods and earth connections should be bonded together with heavy wire or strap so they stay at the same potential during a strike or a fault.
Battery safety
A 12 V storage battery can deliver very high current when shorted. Touching both terminals with dry hands is not normally a shock hazard at 12 V, but a dropped tool or a short can cause severe burns, fire, or even an explosion. Rapid charging or discharging, especially of an unprotected battery, creates heat and gas, so overheating and out-gassing (often of flammable hydrogen) are the hazards. Remove rings and watches, and charge in a ventilated area.
Key facts to memorize
- Black wire = hot, white = neutral, green or bare = safety ground (120 V US).
- Fuses and breakers go in series with the hot conductor only.
- Never substitute a fuse with a higher current rating.
- Discharge power supply filter capacitors before working inside.
- Lightning arrester location: grounded panel where feed lines enter the building.
- Bond all ground rods together with heavy wire or strap.
- Battery shorts cause burns, fire, or explosion; fast charge or discharge causes overheating or out-gassing.
- Voltmeters and leads must be rated for the voltage measured.
Memory hooks
“Black bites, white is the white flag, green is the grass”: black is hot, white is neutral, green is ground. “Series with the hot” keeps the fuse where the danger lives.