Wire-marking systems are used to identify wires in aircraft, shipboard electronic equipment, and
power tool and appliance cables.
Aircraft Wire-Marking Systems
All aircraft wiring is identified on wiring diagrams exactly as the wire is marked in the aircraft. Each
wire is coded by a combination of letters and numbers (figure 3-3) imprinted on the wire at prescribed
intervals along the wire run.
Figure 3-3.Aircraft wire marking.
Look at figure 3-3. The circuit function letter (P in this example) identifies the basic function of the
circuit concerned. The letter P indicates that the wire is in the dc power distribution system of the aircraft.
The wire number, 215, indicates that it is the 215th wire in the dc distribution system. The wire segment
letter (A) identifies the position of each wire segment of the circuit. The wire segments are lettered in
alphabetical sequence and change each time the wire passes through a terminal or connector. For
example, after the wire passes through the first terminal or connector, the segment letter A, as in this
instance, would change to B.
The wire size number (4) is the AN wire size. AN wire sizes have more strands for flexibility and are
slightly different in circular mil area than AWG (American Wire Gauge) wire sizes. The current-carrying
capacity of each is almost the same. The last letter (N) is the ground or phase letter. The letter N identifies
any wire that completes the circuit to the ground network of the aircraft.
In a 3-phase ac power distribution system, a phase letter (A, B, or C) is used as the last letter of the
wire marking. If aluminum wire is used as the conductor, ALUMINUM or ALUM will be added as a
suffix to the wire identification code.
If a wire passes through a connector what portion of the aircraft wire identification number
Shipboard Electronic Equipment Wire-Marking Systems
The following explanation is an example of the type of conductor marking used in shipboard
electronic equipment. These conductors may be contained in cables within the equipment. Cables within
equipment are usually numbered by the manufacturer. These numbers will be found in the technical