Short-circuit the secondary of a current
CAUTION
transformer before you disconnect the meter. An
Before disconnecting a ground strap on
extremely high voltage buildup could be fatal to
equipment supported by shock mounts,
unwary maintenance personnel.
ensure the equipment is DE-ENERGIZED
Open the primary of a potential transformer
and a DANGER/RED tag is installed
before you remove the meter to prevent damage
to the primary circuit due to high circulating currents.
If the grounding strap is broken and the
equipment cannot be de-energized, use a
In most installations potential transformer
voltmeter from the equipment to ground to
primaries are fused, and the transformer and
ensure that no voltage is present.
associated meter can be removed after you pull
the fuses for the transformer. When disconnect-
Maintenance of grounding cables or straps consists
ing the transformer and meter leads, avoid con-
of the following preventive procedures:
tact with nearby energized leads and terminals.
Clean all strap-and-clamp type of connectors
SAFETY SHORTING PROBE
periodically to ensure that all direct
Before you start working on de-energized circuits
metal-to-metal contacts are free from foreign
that have capacitors installed, you must discharge the
matter.
capacitors with a safety shorting probe (fig. 1-3). When
Replace any faulty, rusted, or otherwise unfit
using a safety shorting probe, first connect the test clip
to a good ground to make contact. If necessary, scrape
grounding straps, clamps, connections, or parts
the paint off the metal surface. Then hold the safety
between the equipment and the ship's hull.
shorting probe by the handle and touch the probe end of
When replacing a grounding strap, clean the
the shorting rod to the points to be shorted. The probe
metallic contact surfaces and establish electrical
end can be hooked over the part or terminal to provide
continuity between the equipment and the ship's
for a constant connection to ground. Never touch any
hull. Check continuity with an ohmmeter (the
metal parts of the shorting probe while grounding
reading must be 1 ohm or less).
circuits or components.
Recheck to ensure the connection is securely
It pays to be safe--use the safety shorting probe
fastened with the correct mounting hardware.
with care
If a voltage is present, and the equipment cannot
NOTE: Capacitors not electrically connected to the
be de-energized, you must wear electrical rubber
chassis ground must have their terminals shorted
gloves and use a rubber mat while replacing the
together to discharge them by the use of a shorting probe.
grounding strap.
HAND TOOLS
SWITCHBOARDS AND SWITCHGEARS
Hand tools include all electric-, electronic-,
Safety precautions, operating instructions, wiring
diagrams, and artificial respiration/ventilation
pneumatic-, and hydraulic-powered equipment used in
instructions must be posted near the switchboards and
the repair, maintenance, calibration, or testing of other
switchgears. DANGER HIGH VOLTAGE signs must
shipboard equipment. Handtools can either be installed
be posted on and/or near switchboards, switchgears, and
in a fixed location or portable. You probably have seen
their access doors.
some dangerous practices in the use of hand tools that
could have been avoided One unsafe practice involves
SWITCHBOARD METERS AND
the use of handtools with plastic or wooden handles that
INSTRUMENT TRANSFORMERS
are cracked, chipped, splintered, broken, or
When removing or installing switchboard and
unserviceable. Do not use these tools.
control panel meters and instrument transformers, you
need to be extremely careful to avoid electric shock to
PORTABLE ELECTRIC-POWERED
yourself and damage to the transformers and meters.
TOOLS
Some of the precautions you should follow when
Portable, electric-powered tools should be clean,
working around switchboard meters and instrument
properly oiled, and in good operating condition. Before
transformers include the following:
1-10
