thereafter, he touched the ground lead and
received a serious shock. He was treated for
minor burns on the palm.
VOLTAGES ABOVE 300 VOLTS
All the safety procedures for measuring voltages
below 300 volts also apply when you are measuring
voltages above 300 volts. However, the big difference
when measuring voltages above 300 volts is that you
must NOT hold the test probe while the equipment is
energized. Instead, you must attach the test probes
while the equipment is de-energized. (Refer to table
Electrostatic discharge (ESD) can destroy or
damage many electronic components, including
integrated circuits (ICs) and discrete semiconductor
devices. Since certain devices are more susceptible to
ESD damage than others, warning symbols, shown in
figure 3-1, are now used to identify ESD-sensitive
(ESDS) items. The widespread use of integrated
circuits led to the development of special training
courses in miniature/microminiature (2M) circuit
Certified 2M technicians are trained in procedures
for reducing the causes of ESD damage. The
procedures are similar for all levels of maintenance. If
you are certified in 2M repair, you should follow the
protective measures in table 3-6 to help prevent ESD
damage. Remember, although many sources of
electrostatic charge are of little consequence during
most daily activities, they become extremely important
when you work with ESD material. If you are not
certified in 2M repair, do not attempt to repair any of
For further information on handling ESD
materials, refer to Introduction to Microelectronics,
Navy Electricity and Electronic Training Series
(NEETS), Module 14, NAVEDTRA 172-14-00-84.
Q3. What is the FIRST step in taking voltage
measurements below 300 volts?
Q4. What is the major difference between using a test
probe to measure a voltage above 300 volts and
using it to measure a voltage of 300 volts or less?
Q5. What dangerous effect to electronic components
are EDS precautions designed to reduce or
The electromagnetic spectrum encompasses
everyday uses from commercial power to medical
ALWAYS follow all preliminary safety procedures for measuring voltages below 300 volts before
beginning your measurement.
ALWAYS make sure that the equipment you are working on is de-energized.
ALWAYS follow the tag-out procedures.
ALWAYS discharge all high-voltage capacitors with a shorting probe.
ALWAYS attach the ground probe of the measuring device first.
ALWAYS secure the other probe of the measuring device to the test point to be measured.
ALWAYS make sure that the measuring device is set up for the voltage level and polarity to be
ALWAYS energize the equipment under test, make the measurement, and then de-energize the
Table 3-5.Safety Precautions For Measuring Voltages Above 300 Volts