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Allied Encyclopedia: M25038 Aerospace Cable

Wednesday, March 19, 2014

Allied EncyclopediaM25038 cable is electrical cable for flight critical circuits. These circuits are the ones whose failure or malfunction could lead to catastrophic problems, including engine shut-down or serious damage to the aircraft. Because these cables are so important to the function of the aircraft and the safety of anyone involved, they must meet strict specifications for their construction, and must undergo testing to ensure they can operate even in emergency conditions. You can start learning about M25038 cables by looking at their part numbers. Below is a sample part number, and how it breaks down.

 M25038/1 – 22 – 9 – A

  • M = Defense specification product
  • 25038/1 = Specification sheet number
  • 22 = AWG size
  • 9 = Color (In this case, white. See the “Color” section below for more details.)
  • A = Only for flight critical applications

*Note: M25038/3 cables with heavy wall constructions include an “H” designator in the part number. Although you can tell a M25038 cable’s specification sheet, AWG size, and coloring just by looking at the part number, more information about the construction and performance of these kinds of cables is outlined in the Mil-DTL-25038 specification. Let’s go over some of the important features: Conductor Conductors must meet ASTM B355, Class 27 standards, or ASTM B624 coated with 27% nickel (percentage based on weight). These conductors must be concentric lay for 22 – 12 AWG cables, while cable sizes 10 to 0000 AWG are specified as rope lay. Either option can be true concentric (each layer of stranding alternations direction) or unidirectional (each layer of stranding follows the same direction). You can learn more about conductor stranding, including the differences between concentric and rope lay, here. Primary Insulation M25038 cable is available with glass fiber, ceramic, glass tape, and TFE tape insulation (or a combination of materials that can meet the specifications outlined by the Mil-W-25038 specification, including the ability to withstand temperatures of 650°F for 100 hours). Fiber insulation must be impregnated with a compound such as silicone resin in a manner that ensures it will not enter the conductor stranding (which could interfere with the conductor’s electrical performance). Outer Layer M25038 cable’s outer insulation/jacket consists of fiber glass braid impregnated with PTFE. The PTFE may be extruded, or tape-wrapped and cured. All insulation must fit snugly around the conductor, but also strip cleanly using regular wire stripping tools. Color The insulation’s color is represented with a series of numbers. The first number represents the base color and any subsequent numbers represent the colors of stripes.

Number

Color

Number

Color

0

Black

5

Green

1

Brown

6

Blue

2

Red

7

Violet

3

Orange

8

Gray

4

Yellow

9

White

Performance Requirements Because M25038 aerospace cables are used in flight critical applications, they must withstand short-term emergency conditions, which include resisting exposure to flames and temperatures of up to 2,000°F. Under non-emergency conditions, the cables must exhibit high temperature endurance up to 650°F, with the conductor’s resistance increasing by no more than 15%. The cable must also meet wet dielectric, fluid immersion, cold bend, flame resistance, and thermal shock specifications, among others, to ensure that the cable can continue to operate in a wide range of circumstances and conditions.  M25038 is one of the many aerospace and aircraft cables available from Allied Wire & Cable, with more stock than ever due to Allied’s acquisition of all Alan Wire assets. Alan Wire, based in Irwindale, CA, recently closed its doors after more than 27 years specializing in aerospace and mil spec wire and cable. Learn more about MIL-W-25038 cables by viewing M25038 specifications, or by visiting us in person at the upcoming Aerospace Electrical Systems Expo 2014 in Long Beach, CA.

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