A poor ground is dangerous because it doesn't
performed during unscheduled maintenance are
shown below:
offer full protection; it lulls you into a false sense
of security. The incorrectly wired ground is a
hazard because one of the live wires and the safety
Visually check equipment for loose leads,
ground are transposed. When this happens the
improper connections, damaged or broken
shell of the tool is hot the instant the plug connects
components, etc., before applying power to
into the outlet. You will get a shock unless the
the equipment. This check applies particularly
to new equipment preserved or stored for long
safety ground connects to the grounded side of
periods and equipment exposed to the weather.
the line on a single-phase grounded system, or no
grounds are present on an ungrounded system.
Today, a three-wire, standard, color-coded cord
Conduct a close visual inspection on
with a polarized plug and a ground pin is used.
O-rings, gaskets, and other types of seals when
the equipment under check is a pressurized
In all properly connected new tools, the green
wire is the safety ground. This wire attaches to
component. A visual inspection often reveals
discrepancies that you can correct at that time
the tool's metal case at one end and to the
with minimum labor and parts. Such dis-
polarized grounding pin at the other end. It
crepancies, if left uncorrected, might result in loss
normally carries no current, and is in use only
when the tool insulation fails. When this happens,
of an aircraft or a major maintenance problem.
the safety ground short-circuits the electricity
around the user to ground and protects that
person from shock.
To check the grounding system resistance, you
REVIEW SUBSET NUMBER 1
use a low-reading ohmmeter to be certain the
Q1. What is the ONE rule you should always
safety ground is adequate. If the resistance shows
greater than 0.1 ohm, you should use a separate
follow when working on electric or elec-
ground strap.
tronic equipment?
Some old installations do not have receptacles
that will accept the grounding plug. If you are
working on these, use one of the following
Q2. When working on an electrical system, what
adaptations:
should you do to the power supply?
Use an adapter fitting.
Use the old type plug and bring the green
Q3. Name the manual that you should refer to
ground wire out separately.
for an illustration of the danger areas for
your aircraft.
Connect an independent safety groundline.
When you use an adapter, connect the ground
lead extension to a good ground. Don't use the
Q4. What exterior light is required to be on
center screw that holds the cover plate on the
receptacle. Where separate safety ground leads are
during engine operation?
connected externally, connect the ground first,
and then plug in the tool. Likewise, when
disconnecting the tool, first remove the line plug,
and then disconnect the safety ground. ALWAYS
Q5. When working on a/an
CONNECT THE SAFETY GROUND FIRST
circuit, you need to have a person who is
AND REMOVE IT LAST.
fully qualified in first aid standing by.
UNSCHEDULED MAINTENANCE
Q6. Before touching a capacitor, you should be
Unscheduled maintenance is the performance
sure it is discharged by
of a repair action without a set interval.
Discrepancies found before, during, and after
flight fall into this category. Some of the duties
