Electrical Safety — Respect the Voltage
This Chapter Could Save Your Life
At 400W, your equipment handles voltages and currents that can kill. Valve amplifiers in particular can have 2000-4000V DC on the plates — instantly lethal. Even solid-state gear at 400W produces dangerous RF voltages.
How Little Current It Takes
| Current (AC) | What happens |
|---|---|
| 1 mA | You can just feel it — tingling |
| 10-20 mA | Muscles lock up — you CAN'T let go ("let-go threshold") |
| 50-100 mA | Heart fibrillation — potentially fatal |
| >100 mA | Cardiac arrest, severe burns |
The lethal range is shockingly small: 50-100 mA through the heart can kill. That's less than the current through a dim light bulb. At 240V mains voltage, your body's resistance (maybe 1000 Ω if your hands are damp) would allow 240 mA — well into the lethal range.
Essential Safety Rules
- Never work on powered equipment. Always disconnect power before opening enclosures.
- Discharge capacitors! Large filter capacitors in power supplies can hold lethal charges for hours after power off. Use a bleeder resistor or insulated discharge probe.
- One-hand rule: When near any energised circuit, keep one hand in your pocket. This prevents a current path through your chest (hand-to-hand across the heart is the most dangerous path).
- Use an isolation transformer when working on mains-connected equipment.
- Fuse everything properly. The correct fuse rating is your last line of defence.
- Earth all equipment cases. If a fault energises the case, the earth path should blow the fuse before you touch it.
- Safety interlocks: Amplifier cabinets should have interlocks that cut power when opened.
If Someone Gets Electrocuted
- DO NOT touch them while they're in contact with the electrical source — you'll become part of the circuit
- Disconnect the power if possible, or use a non-conducting object (dry wood, plastic) to separate them from the source
- Call 000 (Australian emergency)
- Begin CPR if they're not breathing and have no pulse
- Treat burns if present
RF Burns
Touching an antenna element, feedline connection, or matching component during transmission can cause painful RF burns. These are thermal injuries — the RF heats tissue from the inside. They can be deep and slow to heal. Never touch any part of the antenna system while transmitting.