How to identify an aircraft wire to understand wire system degradation

If you try to identify an aircraft wire, particularly in service conditions, is not an easy task. However, we know it can assist with understanding details of wire system degradation. With the a variety of codes combined with the difficulty of finding the code on smaller gauge wires can try the patience of a skilled technician. The following is a set of guidelines developed by Lectromec to help with wire identification. Editors Note: This article was updated August 31, 2014 for content clarification.

Read the stamped identification markings, usually about every 12 inches (30 cm) along a wire

If there is no identification marking go to the next main heading
If there is an identification marking the following will help in the recognition

Top or left most alphanumerics give the main wire identification, e.g., MIL-W-22759
Slash number, if used, follows for further identification, e.g., MIL-W-22759/35
Further alphanumerics beyond the slash number give information about gauge, wire color, etc.
Identification codes area different between the military and civilian communities both in the United States and Europe
Go to the wire identification page to find the material or materials used

In some instances there will be a number that is a functional identifier (a wire for a light, etc.)

This identification most likely will not follow any of the wire identification type codes
If available from the airplane’s service or wiring manuals, this number should give an identification of the wire type

Looking to identify a wire? This quick guide can help

Sometimes only a manufacturer’s identification is the only information available

Maybe of limited use even if the manufacturer’s name is on the wire
Contacting the manufacturer might give the material identification
An example with Boeing BMS 13-42A is in the figure above, courtesy of the NTSB TWA 800 Accident report

Cables (e.g., twisted pair, etc.) have a different coding scheme; see the Information about Cable (twisted pair, etc.) wire identification page.

If you are interested in wire system degradation, you may want to read Wire Degradation and Looking in the Arc.

Why is an identification marking not available and what to do

Why isn’t the identification available

The wire is too short
If the wire of interest is in a bundle, the identification could be below another wire
The marking has been worn or dissolved
The wire is covered with dirt, e.g., grease, dust, etc.
If the wire is dirty, careful, quick cleaning may uncover the identification marking
There was no identification marking at the time of manufacture or installation

How to overcome this problem

Check the type of aircraft in order to help identify a wire

See if the aircraft is in the database

Caution – the manufacture date should be checked as changes of wire types during production may have happened and the dates are only approximate
The age of the airplane may offer some further clues (see below)
Caution – the wire listings usually do not include some special wires that are used sparingly

If available, specifications from the aircraft manuals can be used

Caution – the wire may have been replaced by another type and the change was not recorded
Caution – unrecorded changes may have happened during the aircraft’s manufacture

Where the airplane was manufactured may give hints

Polyimide insulation with European constructed wire is somewhat different than most of that from the United States
Other insulation types usually are more similar in construction

Check the construction of the wire

Cross-section the wire and perhaps make a small slice at an angle with the conductor

If there is a tape layer or tape layers of insulation, then some of the material probably is a polyimide

Polyimides usually are tan to brown in color
Some insulation is wrapped tape, e.g., MIL-W-22759/1
The “top coat” sometimes can aid in identification
Check the material information part of the database for more details
See the figure below for an example of tape construction (MIL-W-22759/88)

Example of multi-layer wire insulation

If the material has a layer or layers of extruded material (i.e., completely continuous and uniform)

PVC is layered with Nylon and sometimes glass fiber
ETFE or XL-ETFE usually are single insulation types
XL-PVDF is the outer layer with a cross-linked poly alkene inner layer
Poly-X insulation was extruded with at least two layers and a poly imide”top coat”
Color variations between the layers often can be seen
Check the material information part of the database for more details
See the figure below for an example of extruded construction (MIL-W-5086/7B)

Color identification of the insulation materials may or may not be useful

Color additives are often added to extruded materials
Sometimes aged Nylon will be discolored
Poly imides are tan or brown

Measure the conductor diameter

This can help determine the wire gauge size
Most of the wire is stranded
Go to the stranded wire table at the bottom

Simple chemical and/or physical tests for identification and confirmation

The following procedures should be done only by qualified individuals
Nylon will dissolve in 10% hydrochloric acid and more quickly in concentrated hydrochloric acid

Hydrochloric acid is also known as muratic acid
Care is required when handling this acid
Would be useful if glass fiber layer is not present and as a confirmation

PMDA-ODA dissolves in very caustic or concentrated sulfuric acid solutions

For safety reasons a caustic solution (sodium hydroxide) is preferable
With either solution caution must be used
Dissolution may take some time with either sodium hydroxide or sulfuric acid with stirring
Not know if “T” film is soluble in sodium hydroxide
“T” film has been reported to dissolve in sulfuric acid

Poly-X dissolves in a caustic or concentrated sulfuric acid solutions

Prediction from the structural similarity to PMDA-ODA
Also based on reported weaknesses

PVC will dissolve in solvents used for PVC pipes
Other materials, e.g., PTFE, PVDF, PE, and ETFE, can not be identified as easily as the above insulation with simple tests
Note that XL PE/XL PVDF insulation is thicker than XL ETFE or ETFE

Various instrumental analysis methods

Fourier Transform Infrared Spectroscopy (FTIR)
Thermogravimetric analysis (TGA) and/or Differential Scanning Calorimetry (DSC) may be useful
Relatively small amounts are needed for either method
Much higher level of certainty for identification
Much higher level of certainty for identification
Any instrumental analysis will be somewhat costly

Age of the aircraft and the wire insulation

An aircraft’s age may provide a clue to the insulation type
Some insulation materials usage has been discontinued in newer airplane
Replacement with “older” materials often is done to conform with OEM original specifications
In some cases “older” materials are replaced with other insulation and probably newer types
Some materials have been introduced or discontinued over the years
Some newer materials were introduced while older ones were still being employed
The following list can be used as arough guide especially with many large transport and some military airplanes for the common wire types

PVC/Nylon/Glass was installed up to about 1980 for some aircraft types
PTFE was approved for some uses in the 1960’s but appears to not have been used widey
XL-PVDF/XL-poly alkene was installed up to about 1970 in most airplanes and still may be employed in some cases
“Poly – X” started and stopped being installed in the 1970’s
PEK started and stopped being installed in the 1970’s
Poly imide started to be installed in the early 1970’s and is still being fitted in some new aircraft
XL-ETFE started to be installed in the late 1970’s and is still being used in new aircraft
“TKT” started to be installed in the middle 1990’s and is still being utilized in new aircraft

Overall diameter for various stranded wire sizes-does not include insulation

AWG Size	UK Size code	# of strands	Diameter (min) in	Diameter (max) in	Diameter (min) mm	Diameter (max) mm
26	001	19	0.018	0.019	0.46	0.48
24	002	19	0.023	0.024	0.58	0.61
22	004	19	0.029	0.031	0.74	0.79
20	006	19	0.037	0.038	0.94	0.97
18	010	19	0.046	0.048	1.17	1.22
16	012	19	0.052	0.054	1.32	1.37
14	020	19	0.065	0.068	1.65	1.73
12	030	37	0.084	0.087	2.13	2.21
10		37	0.106	0.111	2.69	2.82
8		133	0.158	0.017	4.01	0.43
6		133	0.198	0.212	5.03	5.38
4		133	0.250	0.268	6.35	6.81
2		665	0.320	0.340	8.13	8.64
0		1045	0.474	0.506	12.04	12.85
00		1330	0.546	0.578	13.87	14.68
000		1665	0.614	0.654	15.60	16.61
0000		2109	0.674	0.718	17.12	18.24

This article was written by the Lectromec technical team. Aircraft wiring is our passion and we strive to make a contribution to the field by sharing our expertise through blogs, podcasts, and videos. We hope you find this information helpful. We also encourage you to submit comments and spur discussions.