The terms Cable Assemblies and Wiring Harnesses are sometimes used interchangeably, mainly because they serve the same electrical function. However, there are significant differences between the two and before getting into more details, here are a few examples.
- Ethernet cables
- Antenna cables
- Ribbon cables (with connectors)
- Power cords
- Various A/V cables, such as HDMI, DVI, RGB, headphone cable, etc.
- Automotive wiring harnesses – behind the dash, under the hood, connecting the lights, etc.
- Refrigerator harnesses
- Aircraft harnesses
- Power supply harnesses that just use wires to connect things but are tied together
An example of something that could be either a cable assembly or a wiring harness, depending on how it is built, is a serial RS232 cable. If you buy one of these as a COTS item, it is likely a cable assembly, complete with over-molded ends for strain relief. However, if you need one quick, all you really have to do is to get two DB9 connectors, three wires cut and stripped to equal length, then connect the two connectors together with the three wires at the correct pin locations, secure the wires with cable ties, and you have a simple wiring harness. With some examples out of the way, time for a few more details:
In the simplest of terms, a cable is a pre-determined group of wires (conductors). They are usually designed with some benefits over just using a bunch of individual wires:
- The wires in the cable can be twisted pairs or triads – helps to neutralize interference
- The wires in the cable can have controlled impedance – very important in data transfer such as Ethernet cables and HDMI cables
- The cables can provide shielding – this can cover the entire cable and/or individual wires as well as individual twisted wires; this helps to eliminate interference
- A metal strand can be run with the wires to provide electrical connectivity between the connectors, as well as strain relief for the cable
- The jacket can be color coded for easy assembly and several materials are available that provide different levels of protection against fire, chemicals, and UV. They also have differing durability and flexibility characteristics. PVC and PTFE (Teflon®) are some of the most commonly used; if you have a specific application look at the others to assess for the best fit
- They are usually cut to length and don’t require extra zip ties or sheathing
Cable assemblies usually consist of cable and connectors on each end. They provide all of the advantages of the cables above, and depending on how the connectors are attached, can be the best option for use outdoors or in other harsh conditions and the best option for high-speed data requirements. They also provide a great way of electrically connecting two PCBs together or a PCB to an external panel when only one connection is needed.
If cable assemblies are so great, why use wiring harnesses? One likelihood is that some cable requirements are not very extensive. It’s just easier and potentially more cost effective to stock wires, create a cable assembly out of them, as needed, instead of stocking several rolls of multi-conductor cables. Another time when it’s really important to use a wiring harness is when you have many branches coming from one connector in a cable. A great example of this is a PC power cable wiring harness; one end connects to the PC power supply, and it has many branches that attach to the hard drive, motherboard, LEDs and so on. A cable assembly would not be the appropriate thing to use here because of all the branches.
If you have a requirement with many branches AND some controlled impedance such as in RF cables, you can include cables within a wiring harness to achieve this. Often the terms wiring harness and cable harness are used interchangeably.
Building wiring harness and/or cable assemblies
Many aspects of building and testing wiring harnesses and cable assemblies are the same. Wires need to be cut to length, stripped, (possibly tinned) and then soldered or crimped to the connector pins or terminal as required. In some applications, insulation needs to be removed to specific dimensions. Some terminations or splices require more customization. ACDi has automated equipment to perform the steps above to produce consistent cables.
Some cables and wiring harnesses require potting in the connector ends for additional strength and resistance to environmental conditions.
Wiring harnesses require the extra step of cutting different length wires, and sheathing them sometimes with built-in bends. Special wiring jigs can be made to assist in this and keep the wiring harnesses consistent.
Testing wiring harnesses and cable assemblies
Building wiring harnesses and cable assemblies is in general a very manual process. It is imperative to test them for proper build. A minimum test for connectivity, shorts and opens should be performed. Additionally, insulation resistance, embedded passive components, and hi-pot testing can be performed to verify compliance. ACDi incorporates Cirrus Harness Test systems with customized tooling to test cable assemblies and wiring harnesses.
ACDi can help with all of your wiring harness and cable assembly needs. For over 30 years ACDi has specialized in the manufacture of a wide variety of wiring harnesses, cable assemblies, and chassis units for commercial, industrial, military, and medical applications. ACDi is certified and listed by UL as a “Wiring Harnesses – Component” manufacturer. ACDi’s quality management system (QMS) is AS9100D/ISO 9001 certified and 10CFR50 Appendix B NQA-1 complaint for the manufacture of safety related nuclear products. ACDi provides in-house training and certification to meet IPC 610, IPC 77111/21, J-STD-001 and IPC/WHMA-A-620 workmanship standards. All wire harness and cable products are subject to 100 percent inspection, test, and verification to ensure compliance with customer specifications prior to shipment.