(b) If adequate isolation cannot be
accomplished, the entire fuel system will be drained and
3-3. Installation of Electrical Connectors and
Common Plugs. Plugs and receptacles are provided
throughout the aircraft to provide a means of connecting
individual components to the electrical system and to
facilitate their removal and installation. Electrical
connectors also are provided at some firewalls,
bulkheads, and decks to provide wire routing through
the aircraft structure and to facilitate removal and
replacement of wiring harness segments. Those
connectors installed in areas of high vibration or in areas
not accessible for periodic inspection are secured with
wire or otherwise mechanically locked to prevent
opening of the connector due to vibration.
a. Types of Connectors. Connectors are
identified by AN or MS numbers and are divided into
classes with the manufacturer's variations in each class.
specification. Some commonly used connectors are
shown in figure 3-4. There are five basic classes of AN
or MS connectors used in most aircraft. Each class of
characteristics. Classes A, B, C, and D are made of
aluminum, and class K is made of steel.
Class B-Connector back shell separates into
two parts lengthwise. Used primarily where
it is important that the soldered connectors
be readily accessible. The back shell is
held together by a threaded ring or by
inserts that are not removable. Similar to a
class A connector in appearance, but the
inside sealing arrangement is sometimes
different. It is used on walls of bulkheads of
connector which has a sealing grommet in
the back shell. Wires are threaded through
tight-fitting holes in the grommet, thus
sealing against moisture.
Class K-A fireproof connector used in areas
where it is vital that the electric current is
not interrupted, even though the connector
may be exposed to continuous open flame.
Wires are crimped to the pin or socket
contacts and the shells are made of steel.
This class of connector is normally longer
than other classes of connectors.
(1) MS connectors. MS connectors as
shown in figure 3-4 are electric connectors with solder or
removable crimp contacts (both front and rear release).
These connectors are for use in electronic, electric
power, and control circuits.
(2) Special-purpose connectors. In addition
to the MS connectors, special purpose types are
commonly found in military aircraft. These are
described in the following paragraphs.
(Cannon KE series). These connectors are similar to
the MS-K series, with the additions of a moisture-
resisting seal. They will mate with MS-K plugs or
receptacles, but retain the moisture sealing feature only
when mated with corresponding KE series plugs or
(b) Subminiature connectors (Cannon
US Series). These connectors, as shown in figure 3-5,
are wire connecting types only; they have no mounting
flanges, but can be mounted with nut and lockwasher.
They are used on instruments, switches, relays,
transformers, amplifiers, etc.
(Bendix SR; Cannon DPD). These connectors, as
shown in figure 3-6, are flanged for panel or equipment
mounting. They consist of an aluminum alloy shell, rigid
or resilient insert, and pin or socket contact. They are
usually potted to protect connections against moisture at
the back of the connector. The mating faces are not
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