CHAPTER 10
ENGINEERING ELECTRICAL EQUIPMENT
MAINTENANCE
This chapter was developed from the GSE3
surfaces must first be penetrated. As mentioned
above, the pins used in the wire wraps are squared
OCCSTDs. However, by reading this chapter, a
off. They have corner edges that will penetrate
GSM will also be able to understand some of the
maintenance requirements of electrical equipment.
the oxide coating of the wire when it is properly
wound on the pin. The edges will also lose their
Upon completing this chapter, you should be
oxide coating when they penetrate the surface of
able to describe the basic techniques of wire
the wire. The junction that is formed is strong,
wrapping, the maintenance requirements and
gastight (tight enough to seal out gases, in
troubleshooting techniques of electrical equip-
addition to liquids), and resistive to corrosion.
ment, and the requirements of lead-acid storage
batteries.
WIRE-WRAP TECHNIQUES
The technique of wire wrapping is also fairly
WIRE WRAPPING
simple. A special solid conductor insulated wire
is required. The use of solid conductor wire
In chapter 3 you were shown some of the hand
ensures that the coil will form tightly about the
tools used for wire wrapping (fig. 3-13). In
pin and remain that way without appreciable slip-
this section we will discuss the principles and
page. The wire is a composition of a silver alloy
techniques involved in wire wrapping.
with a copper coating. Silver offers an advantage
The equipment that you would use the wire-
in that its oxide is almost as conductive as the
wrap technique on has long square pins/posts at
metal itself. Teflon or Meline is usually the
the rear of the female connectors used for logic
insulation used on the wire. Teflon offers an
card inserts. An example is the back-planes of
advantage of very high temperature stability and
ease of cutting (for stripping by automatic
various consoles. These pins are long enough to
machinery). It also has the undesirable trait of the
allow one to three wires to be wrapped on them
insulation gradually receding away from any point
in separate wraps. (A wrap is defined here as a
series of turns of a single solid wire about a pin.)
of continued pressure--a process described as
"cold flow." Teflon-insulated wire in contact with
The female connectors are then interconnected
a pin may eventually result in an intermittent short
from pin to pin by a small, solid insulated wire.
occurring at that point. Meline withstands
This insulated wire may or may not be color
continued exposure to pressure much better than
coded. Machine-wrapped assemblies usually do
Teflon. It is more resistive to cold flow, but does
not contain color-coded wiring. Hand-wired
not have the very high temperature characteristics
assemblies do contain color-coded wiring. (Color-
of Teflon. Meline has become more widely used
coded wire is an advantage in hand-wired
because of the cold flow problem.
assemblies, since each wire becomes more
distinctive and fewer errors are likely to result.)
The first step in wire wrapping is for you to
determine the correct gauge of wire required to
perform the job. Strip off enough insulation to
WIRE-WRAP PRINCIPLES
allow the correct number of turns to be wound
around the pin. Then place the end of the wire
The principle behind wire wraps is a simple
in either a long shallow groove along the barrel
one. For proper conduction to occur between two
of the wire-wrap tool, or insert it in the smaller
metals, the oxide coating that has formed on both
10-1
