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TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
o. Where connection is made to a DC circuit one
g. Rotating machinery must not be loaded or
side of which is grounded, one circuit breaker in the
speeded beyond their ratings.
high side is sufficient. Where neither side is
12-6. Transformers.
grounded, a circuit breaker must be placed on both
Never open-circuit the secondary of a current trans-
sides of the circuit.
former having current flowing through its primary
p. Note identification of all circuit outlets at test
winding because of the resulting high induced volt-
tables and switchboards, and be sure you make the
ages. If a current transformer has no secondary con-
correct connection.
nected load, then the secondary terminals should be
q. Use only portable droplights with insulated
shorted. The secondary windings of both current and
lamp guards and handles.
potential transformers must be grounded.
r. Always test a circuit that you are to work on
for zero volts. Before and after this test, check a
12-7. Wiring and testing.
circuit that is known to be energized so that the
Observe the safety rules below when wiring or testing:
functionability of the tester maybe verified.
a. Never start work or allow anyone else to start
s. Do not rely on the solid insulation surrounding
work on any circuit until you have made certain
an energized conductor to protect personnel.
that the circuit has been properly de-energized,
12-8. Mechanical.
tagged, locked-out and grounded (see para 12-2).
Inspect terminal connections and make sure that
Many power circuit breakers are both opened and
the bolted, soldered, crimped or welded lugs are
closed with springs. These springs may remain
charged even when a breaker has been withdrawn
b. Complete and inspect all wiring before mak-
from its enclosure, and are capable of operating the
ing connection to the power circuit.
breaker. If the breaker is closed, make sure the
c. Before a plugging operation is attempted, the
opening spring is discharged before you approach it
apparatus and circuit must be de-energized by
with your tools or fingers. If the breaker is open,
opening a breaker or a switch.
block it and wire the trip latch. Above all, read the
d. When plugging power, first plug one end of the
manufacturer's instructions so that you can predict
cable into the "load circuit" so that no power is on
the condition of the breaker.
the cable. Then plug the other end firmly into an
energized receptacle. When disconnecting a plug,
12-9. Danger warning and fire.
reverse the sequence above.
Approved danger warnings shall be used to indicate
e. When plugging to a grounded power supply
any temporary hazard, either electrical or mechani-
the first conductor shall be connected in the
cal, and the hazard area shall be sealed off. Under
grounded side of the circuit.
no circumstances shall this area be entered by un-
f. Whenever using a test table to operate electric
authorized personnel until the warning is com-
equipment on which test set controls may be "hot-
pletely removed. Approved warning tags should be
to-ground", stand on an insulated floor mat.
used, and military safety standards should be refer-
g. At least two persons should be present in the
enced for marking hazardous areas. Before attempt-
general area of all testing work of a hazardous na-
ing to extinguish an electrical fire, remove the volt-
ture, so that emergency assistance will be available.
age. Use fire extinguisher recommended for
h. Use only one hand whenever practical when
electrical fires but if none are available, attempt to
working on circuits or operating control devices.
contain the fire with water. Do not use carbon tet-
i. Instruments are likely to be "hot-to-ground",
rachloride in confined areas, because of the poison-
and power shall be removed from them before any
ous fumes that may be emitted.
reconnecting is attempted.
j. Carefully insulate exposed connections.
12-10. Personal protective equipment
k. Under no circumstances shall cables with
For low voltage systems, the following personal pro-
damaged insulation or without terminals be used.
l. Keep wiring off an iron floor. Do not roll trucks
tective equipment is recommended as a minimum:
a. Hard hats--
or other objects over any exposed cable.
m. The frames of all equipment under test or
(1) ANSI Class A--limited voltage protection.
used in test must be grounded before power is ap-
(2) ANSI Class C-no voltage protection.
b. Safety glasses (fig 12-5).
n. Whenever connection is made to power circuits,
c. Safety shoes, steel toe.
proper protection must be afforded to both personnel
d. Rubber gloves.
and equipment by suitable opening devices.
e. Breathing apparatus.


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