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Page Title: Figure 1-10.-Out-of-calibration label.
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that associated metering and control circuits are
Safe practice in most electrical or electronic
maintenance and repair work dictates that all power
supplies must be de-energized. However, there are
times when de-energizing the circuits is neither
desirable nor possible, such as in an emergency
Figure 1-10.-Out-of-calibration label.
(damage control) condition or when de-energizing one
or more circuits would seriously affect the operation
of vital equipment or jeopardize the safety of
No work may be done on energized circuits
without the approval of the commanding officer. The
only exceptions to this policy are in those cases in
which approved instructions issued by higher
authority permit opening or inspecting equipment in
the course of performing preventive maintenance,
routine testing, taking measurements, or making
adjustments that require equipment to be energized.
Testing for voltage with a voltage tester is not to be
considered working on live circuits or equipment
Figure 1-11.-Out-of-commission label.
unless entry into energized panels is required.
When working on live or hot circuits, you must be
injured or killed as the one who doesn't properly use
supervised and aware of the danger involved. The
a safety harness when going aloft to align the
precautions you must take to insulate yourself from
anemometer (circuits HD and HE).
ground and to ensure your safety include the following
actions (these precautions do not apply to circuits and
equipment with less than 30 volts):
Provide insulating barriers between the work
Be sure electrical equipment is de-energized
and the live metal parts.
before working on it. To check a de-energized circuit,
first connect the leads of a test instrument (a voltmeter
Provide ample lighting in the immediate area.
or a voltage tester) across the power source terminals
Cover the surrounding grounded metal with a
of a known energized circuit to ensure that the test
dry insulating material, such as wood, rubber
instrument is working properly. Then connect the
matting, canvas, or phenolic. This material
leads of the test instrument across the power source
must be dry, free of holes and imbedded metal,
terminals of the equipment under test to make sure it
and large enough to give you enough work
is de-energized. Recheck the test instrument on the
known energized circuit to ensure that it is still
working properly.
Coat metallic hand tools with plastisol or cover
When checking to see whether circuits are
them with two layers of rubber or vinyl plastic
tape, half-lapped. Insulate the tool handle and
de-energized, check metering and control circuits, as
other exposed parts as practical. Refer to
well as power circuits. In many cases, metering and
NSTM, chapter 631, for instructions on the use
control circuits are connected to the supply side of a
of plastisol. If you do not have enough time to
circuit breaker or supplied from a separate source. A
apply plastisol or tape, cover the tool handles
check of power circuits on the load side of a circuit
and their exposed parts with cambric sleeving,
breaker may show that they are dead after the circuit
synthetic resin flexible tubing, or suitable
breaker is opened, but such a check gives no assurance

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