Multicore Cables Expand Possibilities in Weight and Space Savings
by John Wadeley
Multicore cables support signals, control, and power in a single compact cable.
A common challenge facing today’s cable/system designers is selecting the correct combinations of signal, power, and control cables that meet unique system requirements whilst working within the space budget available and satisfying the specification requirements imposed by the industry served.
Typically, cable specifications are written around a narrow range of designs with specific functionality loosely classified as signal, power, and control. To complicate matters a plethora of specifications have been written governing these types of cables. The specification authorities are normally International standard organisations, Governments and companies.
The need to be subservient to these specifications will typically drive the designer into choosing from a limiting catalogue of parts listed in the applicable specifications. Typically, as a result, multiple cable constructions will be chosen in combination in order to meet the total system requirements.
The optimum answer is often a multicore cable which can support power, control, and signals, including Ethernet, USB, DVI, or MIL-STD-1553B data bus. Thus, a single cable can often support all the needs of the system in one hybrid design. The challenge is how to integrate these types of cables into industry standards.
Multicore / hybrid cables can also provide internal shielding between sensitive signal lines and noisy power lines to allow both functions to operate successfully within the same cable.
The use of multicore / hybrid cables often significantly reduces the weight and volume that the cabling occupies. These savings, in turn, lead to easier installation, clamping, and maintenance of the cable in the available space, while providing greater choice in routings and system functionality.
One additional trend driving interest in multicore cables is its close association with advanced material science that yields thin-wall insulations and jackets. These products can reduce cable diameters in the range of 30% to 40%, whilst maintaining the mechanical toughness, electrical characteristics and environmental performance of these products when compared to standard-wall cables. The smaller size is often accompanied by reduced weight and improved system functionality.
Choosing the correct cable for the environment to ensure correct fit, form, and function is essential. Parameters such as temperature rating, fluid resistance, mechanical strength, ease of use, and installation all need to be considered carefully. Cable failure normally leads to systems failure, which can be catastrophic.
The primary role of the specification has to be to ensure the correct use of products that satisfy the needs of the application and also exclude products that would be unsuitable.
Custom-designed multicore / hybrid cables, when offered with a wide range of well-proven insulation and jacketing materials, allows the cable design to be optimized to provide the best solution for the environment and application.
Specifications should clearly define the attributes of the cables in key performance areas, but today’s reality is that the approach to achieving this is often feature driven. Such that, the cable is defined by such parameters as wire gauge, materials, stranding, and insulation material / thickness.
Whilst such physical attributes loosely relate to electrical and environmental performance, they also limit the possibilities and flexibility of cabling choices. As good as such specifications are at ensuring the right level of performance; these
requirements are also quite rigid, often excluding the use of the optimum
designs and multicore / hybrid cables.
In essence, military wire and cable specifications say, “If you build the cable my way, it will be suitable for your application.” Another approach is to say, “If the cable has these performance attributes, it will be suitable for your application.” The difference in the two approaches is subtle but critical.
In summary, multicore / hybrid cables are often custom or semicustom in construction and offer many advantages; but appear to be something that the military wire and cable specifications world seems to be uncomfortable with.
A multicore / hybrid cable must be terminated but the connector world has already embraced the multiconductor cable by making contacts available to fit most cable types. Standard military connectors, such as the circular MIL-C-38999 or rectangular ARINC 600, accommodate signal, power and optical contacts, and have backshells to terminate shields and strain relieve the cable. Connectors are widely available by customizing standard connector shells with discrete contacts compatible with the components of the cable.
System or hardware requirements may dictate that the multicore / hybrid cable is terminated according to certain breakouts, such as separate connectors for power and control. The parts required for such breakouts, including heat-shrinkable moulded parts, are available in a range of performance grades to match the environment and offer compatibility with the cable jacket materials.
Moving from Specifications to Performance Requirements
Globally and for every market, there are many specifications attempting to describe the required performance of cables exposed to very similar environments e.g. military ground vehicles.
This approach fails to unify the industry using different tests methods and specifying unique properties to achieve perceived suitability.
This activity in turn leads to a myriad of product families driving up manufacturing costs and reducing availability of the products in the supporting manufacturing industry.
Two things need to change:
Firstly, specification requirements should be unified. Cabling requirements for a military vehicle built by one manufacturer should have similar requirements to cabling used in other military vehicles, especially when functioning in the same operating theatre.
Secondly, specifications must change from Products to Requirements. Creating products is the role of the cable industry since they have the most expertise in this area.
The specification authorities should focus on the requirements for these products in key areas such as mechanicals, temperature, and fluids. The end users will choose the products cheapest and easiest to use by natural selection.
These changes will open the door to innovation and unlock existing technologies in so many ways including the use of multicore / hybrid cables. A whole new portfolio of products will appear which will meet form, fit, and function of the industry whilst offering a greater variety of functionality.