16 March 2018
cause a flashover from the wiring to anything
touching the case, such as your hand.
Electrocution caused by using meters
beyond their voltage rating happens regularly. In
the photo, note that the probes are recessed for
extra insulation — use the right probes for the full
If you use a voltmeter to measure high
voltages, power-down the equipment, discharge
the high voltage points, then attach the meter
to the point being measured. Place the meter
where you can see it. Then, power-up the equipment and
take a reading. That way, you’re not touching the meter
when it’s energized.
Special high voltage probes (such as the Fluke 80K- 40
or B&K HV44-A) are available for the multi-kV voltages
sometimes found in tube gear. Remember, it’s not a race.
Take your time.
Switch to Safety
Finally, follow the “switch to safety” rule long
promoted by the ARRL (American Radio Relay League) in
its literature. One of the ARRL’s early technical pioneers,
Ross Hull, died in 1938 from an electric shock when
working on transmitting equipment. The “Switch to Safety”
campaign began thereafter.
Don’t work on live equipment unless it’s absolutely
necessary, and then take precautions. Follow basic safety
procedures at all times.
Don’t work alone and know how to respond if
someone else does get a shock or burn. CPR courses are
often available through a public safety agency like police
or fire at very low cost or free. Electrical safety classes may
be available through your power utility or an electrician’s
Know how to remove power and show your friends
and family how to remove power in your shop or station.
This all sounds like a lot of bother I’m sure, but you won’t
regret having those skills if they are ever needed.
Static Voltages and ESD
ESD stands for electrostatic discharge. Anyone who
has gotten a shock from walking across a carpet and
n FIGURE 3. The IEC 60001- 4-2 electrostatic discharge
(ESD) waveform (A). The Human Body Model (HBM)
circuit at B is used to perform ESD testing on equipment.
n FIGURE 2. Voltage ratings are shown next to a
voltmeter’s probe jacks (1,000V DC and 750V AC).
Exceeding these voltages can result in a flashover, also
presenting a severe electrocution hazard.
Avoid Crack Attacks
If you’re like most electronic-ers, you never throw anything away
— especially test instruments and accessories. In the world of high
voltage, this can be dangerous.
As probes, fixtures, and connectors age, their insulation can
become brittle and crack. That crack compromises the insulation, and
you can even come in direct contact with the internal wiring.
Before beginning a high voltage project, carefully inspect your test
probes and other equipment. Make sure the insulation is clean, flexible,
and not scuffed or cracked so it can protect you as you expect.
PRACTICAL TECHNOLOGY FROM THE HAM WORLD