Electrical cables, looms, and wiring harnesses – you hear these terms in the aircraft and aerospace industry, but what are they? What are the differences?
Essentially, the only difference is in nomenclature. An electrical wiring harness, also known as a wire harness, cable harness, cable assembly, wiring assembly or wiring loom, is an assembly of electrical cables or wires which transmit signals or electrical power throughout an aircraft. The term “electrical cable” is a reference typically found in military applications, whereas the term “wiring loom” is commonly used in a European context (primarily Great Britain – think Rolls-Royce), and in the commercial airline world you find these products typically referenced as electrical wiring harnesses or wire harness assemblies.
“Cable” was originally a term used for a nautical line or length of measure. Thick metal or non-metal cable lines were, and still are, used to secure large objects. As technology progressed the phrase electrical cable, then electrical wiring harness developed. This terminology helps to avoid product confusion. (although, as previously noted, the term electrical cable is still common in the military world). It should also be noted that the phrase “cable” is also used with wire to create a wiring harness (i.e. shielded jacketed cable).
Fabrication of Electrical Cables & Wiring Harnesses
A wiring harness consists of conductor wires that are contained in insulated coverings. These jacketed cables can be individuals, twisted pairs, triplets, etc. Manufacturing and fabrication of electrical wiring harnesses basically consists of:
- Cutting wire to appropriate lengths
- Being laid out on 1:1 form boards
- Wire jackets are then grouped together in bundles (may be twisted or parallel lay)
- Secured with tape and/or lacing ties with breakouts as required
- Termination of ends (involving backshells, contacts, and connectors)
- Sleeving or over-braiding with protective materials (for closed bundle applications)
- Marking and identification
- Final and in-process inspections. (Note that manufacturing and inspection processes must conform to the recognized IPC/WHMA-A-620 standards)
Of course, these highlights have been overly simplified for the sake of this brief article. Wiring harness construction varies greatly, depending upon application and requirements. A great deal of engineering is involved regarding specific application, mechanical features, and electrical requirements. Weight, abrasion resistance, vibration, exposure to fluids & moisture, EMI protection, and consideration of repairability (to name a few) must also be taken into account. Harness assemblies can be summarized into a few basic configurations: open bundle, closed bundle, and overmold designs. More on these in future articles.
Another interesting note is that the manufacturing and fabrication of electrical harnesses is still primarily done by hand, by skilled technicians. While some of the processes are automated (wire cutting, laser marking, automated testing, etc), actual hands-on construction is still required for a great deal of the manufacturing process.
In the aerospace industry, aircraft can contain literally miles of wiring harnesses. Applications include engine, fuselage, wing, landing gear, avionics, and a host of other functions. Outside of aerospace, wiring harnesses find endless uses in the automotive, space, and industrial arenas.
About the Company:
kSARIA is an AS9100:D and ISO9001:2015 registered company with facilities in Methuen, MA and Fort Worth, TX. The company manufactures harsh environment fiber optic and electrical cable assemblies and harnesses. kSARIA also offers turnkey installation services of fiber optic and electrical cable for military and aerospace applications as well as Certified Fiber Optic Training. In addition to manufacturing, training, and services they also provide Part 145 repair services such as check & test, overhaul and repair, and S/B incorporation for many of the aircraft electrical wiring harnesses in service today (FAA No.: OI0R891N, EASA: EASA.145.5897, CAAC No.: F00100406).