MIL-spec were initially developed to standardize wires and cables used in military equipment. For many years, wires used in aircraft met MIL-W-5086 mil-spec and SAE-AS50861 standards superseeding them. They were manufactured with the use of tin-coated copper conductors rated at 600 volts and temperatures of 105°C and various insulating coatings including polyvinyl chloride (PVC). The PVC insulation provided resistance to abrasion, among many other things. Still in production, MIL-W-5086 cables in their various types of conductors and jacket constructions are used, apart from the aircraft in other applications that require resistance to abrasion, cut-through, impact, chemicals, and fuels. They are gradually replaced by those made in accordance with Mil-W-22759 standard due to toxic fumes generated by PVC insulation in the event of a fire. The Mil-W-22759 standard transitioned to SAE AS22759 in 2004 and the original military standards were canceled. These two standards are essentially identical, and even today refered to as M22759 standards. They cover a wide range of single conductor wires of the following characteristics:
Conductors: stranded conductors in a range of sizes, made from plated copper or plated high-strength copper alloys with different types of plating including:
- Tin plating: Commonly used because of its lower cost, tin plating improves solderability and corrosion resistance.
- Silver plating: Silver plating has better high-temperature properties than tin-plating, and silver reduces wire resistance, improves high-frequency skin effect, and has good solderability.
- Nickel plating: Nickel plating has good high-temperature properties and excellent corrosion resistance, but you can't join it except by using a special solder flux or crimped joints.
- Copper alloys: Alloyed copper wires have a higher tensile strength, good conductivity, and resist softening at higher temperatures than copper.
Insulation: Different insulation materials used the most common ones including:
PTFE: Polytetrafluoroethylene is a fluoropolymer with good high-temperature properties (up to 260 C), excellent chemical resistance, and a low coefficient of friction.
FEP: Fluorinated ethylene propylene is a transparent fluoropolymer with excellent low friction properties and a maximum usable temperature of 200 C.
ETFE: Ethylene tetrafluoroethylene is a strong and lightweight fluorine-based plastic with a maximum temperature rating of 150 C.
XL-ETFE: A cross-linked version of ETFE that has thermoset properties and slightly improved high-temperature characteristics.
FP/PI tape: A high-temperature insulating tape made from a fluoropolymer, such as Tefzel™ and polyamide insulation.
Jackets & Braiding: Some M22759 wires have an external jacket or braid for improved abrasion resistance and protection. Jacket materials include PTFE, XL-ETFE, polyvinylidene fluoride (PVDF), and polyamide (PI). Braid materials used are PTFE coated fiberglass.