Closed Bundle and Overmold Electrical Harness Configurations.
This article is a continuation of our wire harness construction series. As a follow up to our previous article on Wire Harness Construction and Open Bundle Configurations (Click here to read Part 1), the following will discuss the characteristics of the closed bundle and overmolded harness designs.
Closed Bundle Wiring Harnesses
Closed Bundle vs. Open Bundle: While layup, wire preparation, and termination are much the same, the primary difference between the two configurations is the use of an outer braid or protective sheathing. As the name implies, the cable jackets of the closed bundle harness are secured within an over braid or other protective material. While the open bundle design offers greater repairability, the closed bundle offers improved durability. During the layup process, the wire cables can be twisted together during the branch bundling, which gives the harness added bend and flexibility.
Although closed bundle harnesses typically have limited repair options, their configuration is ideal for hostile environments. Harness branches are enclosed with materials that protect the inner wire jackets and conductors from mechanical damage and electrical (EMI) compromises. The outer protection can consist of a variety of materials. Outer sheathings include heat shrink sleeving, conduit, tubing, or spiral wrap.
Over braiding is another option that offers exceptional protection. Over-braiding includes metal, Nomex®, PEEK™, Kevlar®, and other protective materials. As an example, an inner metal braid may be applied for EMI protection, and then a second layer of PEEK or Nomex® as an added protection against chaffing. As an added bonus, many of the braiding options are not only durable, but light weight as well. Over braids are available in a range of colors for on-engine identification. A contrasting tracer braid can also be incorporated during the braiding process.
Closed bundle harnesses are most commonly found on gas turbine engines, hot engine sections, fuel quantity, and landing gear applications.
Overmolded Wiring Harnesses
As an added feature, backshells and junctions can be potted or encapsulated with pottable silicones or expandable silicone foam. The overmolded electrical wiring harness design’s molded exterior offers an extra measure of durability, strength, vibration, and moisture resistance.
The overmold design is a sub-set of the closed bundle wire harness family of electrical cables. This protective encapsulation is applied during the manufacturing stages using mold presses and curing ovens. While it does limit the harness repairability, it provides terrific durability and is ideal protection for severe environments and applications.
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).