Electrical Shock Protection
The 2022-2026 Technician License question pool asks...
T0A06: Q. What is a good way to guard against electrical shock at your station?
A. Use three-wire cords and plugs for all AC powered equipment
B. Connect all AC powered station equipment to a common safety ground
C. Install mechanical interlocks in high-voltage circuits
D. All these choices are correct
It won’t shock you to realize that electrical safety is no joke in amateur radio. The 120 VAC that most home stations feed into a power supply is sufficient to kill you dead. And many advanced stations operate with 240 VAC. So, it behooves us amateurs to have at least the basics of electrical safety well understood. That’s why this question is in the pool, even though the answer may be obvious to anyone with the most fundamental comprehension of good safety practices with electricity.
Option A: Yes! This is a great safety practice. Two of the wires in a three-wire cord and plug carry the electric current for powering an appliance (usually color coded white and either black or red). The third wire, usually color coded green, provides an electrical ground connection from the chassis of the device for safety. If any internal component of the device should contact the chassis and thereby produce a dangerous shock hazard for anyone coming in contact with the device, the safety ground connection shunts that current to electrical ground to reduce the possibility of electrical shock.
Option B: Yes again! (OK, you see where this is going.) All AC powered “boxes” of your station should be connected to a common safety ground. The use of a single common ground point avoids any variation among the individual component ground level potentials (voltages). If some variation in ground level potential exists among different pieces of equipment, undesired currents can flow between components (“ground loops”) and offer the possibility of electrical shock to the human operator.
Option C: Of course. Many circuits, such as those within a power supply appliance, will often employ a mechanical interrupt on the chassis of the appliance. This way, when the cover is removed from the appliance a switch automatically interrupts the power connection, reducing the possibility of accidental shock.
And a bonus option not in these question responses: Use a ground-fault interrupter circuit. The old ground-fault interrupter (GFI) circuit is a great way to help avoid electrical shock from AC sources. Also known as the ground-fault circuit interrupter (GFCI), you can identify these electrical outlets by the inclusion of “Test” and “Reset” buttons on the faceplate.
The GFI outlet works by constantly monitoring the level of current flowing out of the outlet
circuit and the level of current flowing back into the circuit. In normal circumstances the “outbound” current and “inbound” (return) current should be equivalent. But if an imbalance between the two levels occurs – such as when a ham radio operator accidentally sticks his tongue to the unprotected 120VAC wire feeding the station power supply while also standing barefoot in a puddle of ale recently spilled on the floor of the shack – well, you get the idea.
The imbalance of monitored currents that results due to some of the supplied current flowing through tongue-body-ale-ground instead of back into the GFI outlet causes the GFI circuit to be interrupted, tripping much like an overloaded circuit breaker and terminating the flow of electric current in the circuit.
So, short out a GFI circuit anywhere and it will trip the interrupter and possibly save your life. Or at least your tongue.
The answer to this question “What is a good way to guard against electrical shock at your station?” is “D. All of these choices are correct.”
Disclaimer: Ham Radio School does not recommend, endorse, sanction, or otherwise suggest licking power cables or any other electrical supply or component whether or not supplied by a GFCI outlet.
-- Stu WØSTU