If you are familiar with the wiring on avionics, airframe, aerospace, and defense applications it’s likely you are acquainted with the NEMA WC 27500 military specification, also referred to as, mil-spec cable M27500 and MIL-DTL-27500. This particular cable spec designates both shielded and unshielded cables in a wide variety of constructions built with SAE AS50861 (M5086), SAE AS22759(M22759), SAE AS81044(M81044), SAE AS81381(M81381), SAE AS8777 (M8777) inner conductors. Under the SAE spec, the conductor size, insulation form, conductor count, shielding material, and jacket compound may all be specified.
When producing these cables they must be QPL approved, along with the basic component wires within the cable. The manufacture of the finished M27500 cable must be a QPL approved manufacture and provide proof that QPL approved inner wires were used to construct the product. During the last SAE meeting members agreed to add the following to the spec information so inner wires that fall under the same lot number had to be tested once instead of each leg individually.
Sampling of the basic wire shall be in accordance with the sampling plan of the basic wire specification. For cables containing more than one conductor, if the same lot of component wire is used to produce the white and striped legs, then test information is only required for that one basic wire. Once striped, the component wire becomes part of the cable lot and is not required to be completely retested and have new reports. Additional impulse dielectric testing in accordance with the basic wire specification shall be performed when a potentially degrading operation (i.e., thermal, mechanical, or chemical in nature) has been performed subsequent to the original test.
These high performance cables range in size from one to fifteen conductors from 26 to 2/0 gauge and can adapt to a wide variety of operating environments. Utilized on aircrafts and ground support equipment, the conductors must be color coordinated per the specs color call out.
One of the most unique things about this particular mil-spec cable callout is perhaps the fact you can determine the components that make up the cable just by observing the part number call out. For example, mil-spec cable M27500-20RC2S09 is a 20 gauge (20) cable, composed of two(2) M27759/11 inner conductors (RC), completed with a round single silver plated copper shield(S) and a single extruded white FEP jacket(09). For an easily converted break down reference sheet of these cables see M27500.
The shielding for the NEMA WC 27500 are provided in a variety of styles to meet temperature ratings from 150°C to 400°C. Material such as Tinned Plated Copper(TPC) round braid, Silver Plated Copper (SPC) Round braid, Stainless Steel, SPC Alloy Round, Nickel Plate Copper(NPC) Alloy Round, along with flat braid options in NPC, SPC, TPC, and Nickel-Chromium Alloy are used to construct the cables shielding. You will also find the shield is provided in either a single or double shielding option depending on the designated letter found within the part number that depicts the shielding selection.
The cables jackets also feature either a single of double jacket option in an arrange of materials including PVC, FEP, PTFE, Polyamide Braid Over Polyester Tape, Polyester Braid over Polyester Tape, Extruded PVDF, Polyimide over FEP wrapped Polyimide tape, ETFE, PTFE Tape Over Polyamide Braid, extruded ECTFE, extruded PFA, and Modified XLETFE all of which are placed over the cable to provide protection to the inner components.
These special purpose electrical cables can bring versatility and protection to your aerospace and ground systems. WireMasters, one of the top wire, cable, and connectivity distributors in the industry are masters of the NEMA WC 27500 cables with an assortment of these products in-stock with same day shipping offered. OPL’d for certain constructions WireMasters, their sister company WyreTek, or the multiple manufactures they were closely with such as; Harbour, RSCC, Specialty Cable, Nexans, T/E Connectivity along with others can help offer short lead times to assist you in meeting tight deadlines especially in crucial AOG situations.