Figure 1-10.-Out-of-calibration label.

that associated metering and control circuits are

de-energized.

LIVE CIRCUITS

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

personnel.

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

CHECKING FOR ENERGIZED CIRCUITS

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

room.

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

1-11