Allied Encyclopedia: M55021 Cable

M55021 cable is 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Until July 2011, M55021 cable was regulated according to the Mil-C-55021 spec, but that has been superseded by the MIL-DTL-55021 specification and, most recently, the ANSI/NEMA WC 55021-2013 standard. M55021 is still commonly called out by the older mil-spec names after many years in use.

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, however, must be shielded, but jacketing is optional.

M55021-Cable

M55021 Cable

Depending on the jacket material, M55021 cable can be used in temperatures ranging from -40°C to 105°C for PVC and Polyamide jacketed cables, or -65°C to 200 °C for PTFE and FEP jacketed cables. Keep in mind that Polyvinylchloride (PVC) insulation or jacketing should not be used for aerospace applications.

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

Typical M55021 cable part number

This part number can be broken down into six sections:

  • Wire Type – “Wire type” 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:

Letter Wire Specification Letter Wire Specification
B M16878/1 EE NEMA HP3 (M16878/5)
C M16878/2 BJ M16878/17
D M16878/3 CJ M16878/18
E NEMA HP3 (M16878/4) DJ M16878/19
  • 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 Size Stranding
26 AWG – 30 AWG 7 Strands
12 AWG – 24 AWG 19 Strands
10 AWG 37 Strands
  • Conductor Material -Therearethreeletteroptionstoidentify 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:

Code Color Code Color
0 Black 5 Green
1 Brown 6 Blue
2 Red 7 Violet
3 Orange 8 Gray
4 Yellow 9 White
  • 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:
Letter Covering Letter Covering
U Unjacketed and unshielded S Shielded and unjacketed
P Polyvinylchloride (PVC) Jacket SP Shielded and covered with PVC Jacket
F Fluorinated Ethylene Propylene (FEP) Jacket SF Shielded and covered with FEP Jacket
J Polyamide Jacket SJ Shielded and covered with Polyamide Jacket
T Polytetrafluoroethylene (PTFE) Jacket STW Shielded and covered with wrapped PTFE Jacket
STX Shielded and covered with extruded PTFE Jacket
  • 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. Print will indicate 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” – First wire base color is white, first stripe is black, and second stripe is yellow

903” – Second wire base color is white, first stripe is black, and 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 the part number 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!

About awcwire
Allied Wire & Cable is a value-added manufacturer and distributor of electrical wire and cable, tubing, and more. We are a family owned and operated company, serving a wide range of industries, including the military, automotive, aerospace, and telecommunications markets. Allied is headquartered in Collegeville, PA. Additional locations can be found across the US, in Merrimack, NH, Tampa, FL, Pewaukee, WI, and Las Vegas, NV. For more information on Allied, visit our main website at www.awcwire.com.

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