What is M55021 Cable?

M55021 cable is a mil-spec electrical cable intended for use in the internal wiring of electrical equipment. Until July 2011, M55021 cable was regulated according to the Mil-C-55021 spec but has since been superseded by the MIL-DTL-55021 specification, and most recently, the ANSI/NEMA WC 55021-2013 standard.

Construction

M55021 cable is available in a variety of constructions, including twisted pairs and triples, which can be any combination of shielded or unshielded and jacketed or unjacketed. Singles must be shielded, but jacketing is optional.

The M55021 cable's temperature range depends on the jacket material. If it has a PVC or Polyamide jacket, the temperature range is -40°C to 105°C. If the jacket is PTFE or FEP, the temperature range is -65°C to 200 °C. Keep in mind that Polyvinylchloride (PVC) insulation or jacketing should not be used for aerospace applications.

Identification

If you had no prior knowledge of M55021 and only had the cable in front of you, you would still be able to figure out a lot about the cable if you know how to break down the part number. A typical M55021 part number looks like:

E24C904-903-9STW

This part number can be broken down into six sections:

• Wire Type— This refers to the basis of the cable’s construction. The inner components of M55021 are built to M16878 specs (or newer NEMA HP3 standards), and knowing which type of M16878 wire is inside will give you more information on your specific M55021 cable. These types range from M16878/1 to M16878/5 and M16878/17 to M16878/19 and are identified in the part number by letter symbols.

Here are the letter combinations and the corresponding M16878 wire:

• Conductor Size— This number identifies the AWG size of the wires in this cable. This table shows the conductor sizes and stranding available for M55021:

• Conductor Material— There are three-letter options to help identify the conductor material:
  • “C” for Copper
  • “S” for Copper Clad Steel
  • “H” for High Strength Copper Alloy

• Color Code— The first number to appear is the base color of the wire, and the second and third indicate stripes. Two groups of numbers indicate a twisted pair and three groups indicate a twisted triple. The color code designators for wires 2 and 3 of a twisted pair and triplet are separated by a dash, but for single shielded and single shielded and jacketed constructions, a dash would not be present in the part number.

Here are the color codes:

• Covering over Components— The covering refers to the shielding and jacket materials. M55021 shields consist of a braid made with the same material as the one used for the conductors. The covering can be identified by either one, two, or three-lettered symbols:

• Identification Method— This cable can be identified by marking intervals of 1 to 3 feet on the outer jacket of the cable or by marker tape placed under the shield or jacket of any of the wires for unjacketed cables. The print will indicate the Military Specification number, manufacturer's CAGE number, type of designation, and the year of manufacture.

For example, let’s break down E24C904-903-9STW:

• E— wire type is NEMA HP3 (M16878/4).
• 24— 24 conductors in the cable.
• C— Copper conductor.
• 904— The first wire's base color is white, the first stripe is black, and the second stripe is yellow.
• 903— The second wire base color is white, the first stripe is black, and the second stripe is orange.
• 9— Third wire base color is white
• STW— Shield consists of a braid made with the same material used for the conductors and tape wrapped in a PTFE jacket.

Since you’re a pro at breaking down M55021 part numbers now, it should be easy to identify the cable’s contents right away! Knowing how to read part numbers will aid in choosing the correct wire for your use. Visit Allied’s MIL-C-55021 cable part number builder to create the wire you need and request a quote!