2014 Tech study guide: electrical safety

Several changes were made to this section that I don’t like. For example, the question pool committee removed the question about 30V being the commonly accepted value for the lowest voltage that can cause a dangerous electric shock. The question about 100 mA being the lowest amount of electrical current flowing through the body that is likely to cause death was removed from the 2010 question pool, so now there are no questions at all about these values. I’m leaving them in the study guide, though, because I think they’re important.

The committee also removed the question about charging a 12 V battery by connecting it to your car battery and running the engine. I’m all for removing that question. It was replaced by a question about what might happen if you short the terminals of a 12V battery…Dan


When operating or working on amateur radio equipment, it’s possible to come into contact with dangerous voltages and currents. Because it would be a shame to lose a single person, it’s important to know how to be safe when working with electricity. Having said that, 30 volts is the commonly accepted value for the lowest voltage that can cause a dangerous electric shock, and 100 mA is the lowest amount of electrical current flowing through the body that is likely to cause death. These are not very large values.

All of these choices are correct when considering how current flowing through the body can cause a health hazard (T0A02):

  • By heating tissue
  • It disrupts the electrical functions of cells
  • It causes involuntary muscle contractions

Three-wire electrical outlets and plugs are safer than two-wire outlets and plugs, and you should use three-wire plugs for all of your amateur radio equipment. The third wire provides an independent, or safety ground. Safety ground is connected to the green wire in a three- wire electrical AC plug. (T0A03)

All of these choices are correct when choosing a good way to guard against electrical shock at your station (T0A06):

  • Use three-wire cords and plugs for all AC powered equipment
  • Connect all AC powered station equipment to a common safety ground
  • Use a circuit protected by a ground-fault interrupter

Individual pieces of equipment may have their own fuses to protect that piece of equipment should something happen that causes that equipment to draw excessive current. The purpose of a fuse in an electrical circuit is to interrupt power in case of overload. (T0A04) When replacing a fuse, always replace the blown fuse with a fuse of the same type and value. It is, for example, unwise to install a 20-ampere fuse in the place of a 5-ampere fuse because excessive current could cause a fire. (T0A05)

If you plan to build your own equipment, be sure to include fuses in your designs. A fuse or circuit breaker in series with the AC “hot” conductor should always be included in home-built equipment that is powered from 120V AC power circuits. (T0A08)

Whenever you’re working on equipment, be sure to disconnect it from the power lines, and even then be careful working around a power supply’s capacitors. If a power supply is turned off and disconnected, you might receive an electric shock from stored charge in large capacitors. (T0A11)

Finally, it’s necessary to take precautions when using batteries to power your amateur radio station. Conventional 12-volt storage batteries present several safety hazards. Shorting the terminals can cause burns, fire, or an explosion (T0A01), explosive gas can collect if not properly vented (T0A09), and, if a lead-acid storage battery is charged or discharged too quickly, the battery could overheat and give off flammable gas or explode. (T0A10)


  1. Fred Becchetti says:

    Yes important to note it’s current that causes death (or in effect electrical energy dissipated at heart/nerves).

    While 30 v is generally considered “safe” for human contact, A GE engineer I believe, electrocuted himself with a 6 v car battery during a”safety” demonstration (as he grounded himself too well)..or is that an urban legend?? ) Again too much current thru heart (car battery can drive hundreds of amps..so stray 0.1 amp thru heart etc. is probably possible under special circumstances).

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