--- title: Designing Cable Assemblies for EMI-Sensitive Applications description: Learn how to design cable assemblies for EMI-sensitive applications using proper shielding, grounding, routing, connectors, and EMC testing. image: https://blog.epectec.com/hubfs/blog/cable-assembly-designed-for-emi-sensitive-applications.jpg --- [![Epec Engineered Technologies](https://www.epectec.com/images/logo.png "Epec Engineered Technologies")](https://www.epectec.com/) [![Epec Engineered Technologies](https://www.epectec.com/images/logo.png "Epec Engineered Technologies")](https://www.epectec.com/) - [Articles](https://www.epectec.com/articles/) - [Blog](https://blog.epectec.com/) - [Webinars](https://www.epectec.com/webinar/) - [Videos](https://www.epectec.com/videos/) - [Case Studies](https://www.epectec.com/case-studies/) - [News & Events](https://www.epectec.com/news/) - [Customer Portal](https://system.netsuite.com/c.406760/site/NSlogin.html) - [About](https://www.epectec.com/about/overview/) - 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[Tweet](https://twitter.com/share) Electromagnetic interference (EMI) can be one of the most frustrating problems to diagnose in a [custom cable assembly](https://www.epectec.com/cable-assemblies/). The cable may be built exactly to print, pass continuity testing, and function perfectly on the bench, only to experience intermittent problems once installed in the finished system. Motors, power supplies, switching circuits, radios, pumps, and even neighboring cables can introduce electrical noise that was never apparent during initial testing. For this reason, designing a cable assembly for an EMI-sensitive application requires looking beyond the cable itself. [Connector selection](https://info.epectec.com/guides/10-ways-to-select-the-right-connector-for-your-custom-cable-assembly), [shielding](https://www.epectec.com/cable-assemblies/shielded-cables.html), grounding, cable routing, nearby electronics, mechanical movement, and workmanship can all influence electromagnetic compatibility (EMC). Just as importantly, engineers from different roles may look at the exact same EMI problem from very different perspectives. Understanding each of those perspectives can help engineering teams identify problems earlier and develop cable assemblies that perform reliably in the actual application. ![Shielded cable assembly designed for EMI-sensitive applications](https://blog.epectec.com/hs-fs/hubfs/blog/cable-assembly-designed-for-emi-sensitive-applications.jpg?width=800&height=500&name=cable-assembly-designed-for-emi-sensitive-applications.jpg) *Shielded custom cable assembly designed to help reduce electromagnetic interference in EMI-sensitive applications.* ## Why Are Cable Assemblies Susceptible to EMI? EMI is unwanted electromagnetic energy that interferes with the normal operation of an electrical or electronic system. EMC refers to the ability of equipment to operate correctly within its electromagnetic environment without producing unacceptable interference that affects other equipment. [![Download Our Guide on Overcoming EMI/EMC Challenges for Cables](https://no-cache.hubspot.com/cta/default/707152/57032398-4cb9-4278-a489-712774beaeaa.png)](https://cta-redirect.hubspot.com/cta/redirect/707152/57032398-4cb9-4278-a489-712774beaeaa) A cable assembly can be both a receiver and a source of EMI. Long conductors can behave like antennas, picking up electromagnetic energy from nearby equipment. At the same time, signals traveling through a cable can radiate energy and potentially interfere with surrounding electronics. This becomes especially important when a cable carries low-level sensor signals, high-speed data, or communication signals near high-current or electrically noisy devices. ## Options for Improvement EMI performance can be improved through several cable design techniques. Braided shields, foil shields, or a combination of the two can provide protection against electromagnetic noise. [Drain wires](https://blog.epectec.com/wire-harness-drain-wires-solid-or-stranded) provide a practical method of terminating a shield to ground and may be constructed using either solid or stranded conductors depending on the application. Twisted pairs can also help reduce noise with lay lengths of 1 inch or less. Depending on the system, passive components such as ferrites, chokes, and transient voltage suppression (TVS) diodes may also be incorporated to help suppress unwanted electrical energy. Conductive gaskets and other specialty materials can extend this shielding approach through [connectors](https://www.epectec.com/articles/changing-and-crossing-cable-assembly-connectors.html) and enclosure interfaces where gaps could otherwise compromise the overall shielding system. The basic principle behind many of these techniques is similar to a Faraday cage. The objective is to surround sensitive conductors with a conductive barrier and provide a controlled path for unwanted electromagnetic energy rather than allowing that energy to interfere with the signals inside the cable. ## How EMI and EMC Performance Is Tested Understanding how a cable assembly will eventually be tested is important because EMI and EMC qualifications can evaluate several very different characteristics. - **Radiated emissions** testing measures electromagnetic energy emitted by a device or system into the surrounding environment. Testing is commonly performed in a controlled environment such as an anechoic or semi-anechoic chamber using calibrated antennas and measurement equipment. If excessive energy is radiating from a cable or connector, shielding and grounding may need to be reconsidered. - **Radiated susceptibility**, also called radiated immunity, evaluates the opposite condition. Instead of measuring what the system emits, technicians expose the equipment to controlled electromagnetic fields and monitor whether it continues operating correctly. - **Conducted emissions** testing evaluates unwanted electrical noise traveling through cables and conductors rather than through the air. Conducted susceptibility or immunity testing introduces controlled disturbances onto those conductors to determine whether the equipment can continue functioning properly. - **Electrostatic discharge (ESD)** and voltage transient testing evaluate how the system responds to short-duration electrical events. These tests can expose weaknesses in grounding, protection circuitry, connector design, and component selection that may not appear during normal operation. ![Anechoic testing chamber ](https://blog.epectec.com/hs-fs/hubfs/blog/anechoic-chamber-testing.jpg?width=800&height=500&name=anechoic-chamber-testing.jpg) *Anechoic chamber testing helps evaluate electromagnetic emissions and immunity in a controlled environment.* What makes EMI testing challenging is that the source of failure is not always obvious. A cable can appear perfectly functional until the complete system is operating inside the test environment. This is where different engineering perspectives become valuable. ## The Electrical Engineer's Perspective: Start with the Requirements From an electrical engineering standpoint, EMI and EMC requirements should be understood as early as possible. Before the cable cross-section is established, determine which performance standards apply, how the system will be tested, and what constitutes a passing or failing result. Waiting until qualification testing to begin thinking about EMI protection severely limits the available design options. [Connector selection](https://www.epectec.com/articles/choosing-the-components-for-your-cable-assembly.html) is especially important. Connectors should provide appropriate shielding and grounding provisions for the application. Manufacturer datasheets should be reviewed carefully to understand recommended termination methods and how the connector is intended to interface with the shield and chassis ground. The cable construction itself should then be developed around the electrical requirements. This may include twisted pairs, individual or overall shields, drain wires, controlled conductor spacing, or multiple layers of shielding. For particularly sensitive applications, using both [foil and braided shielding](https://blog.epectec.com/overview-of-the-shielded-cable-process) may provide advantages. Foil provides excellent coverage, while braid offers mechanical durability and a low-resistance path to ground. The correct solution depends on frequency, flexibility, environmental requirements, and the electrical characteristics of the system. ![Sectioned cable showing the internal conductor](https://blog.epectec.com/hs-fs/hubfs/blog/sectioned-cable-showing-the-internal-conductor.jpg?width=800&height=500&name=sectioned-cable-showing-the-internal-conductor.jpg) *Sectioned cable showing the internal conductor arrangement and shielding layers used to help control electromagnetic interference.* ## The Quality Engineer's Perspective: Find the Source of the Noise When a cable assembly is exhibiting EMI problems or is at risk of failing qualification, the quality engineer's priority shifts toward troubleshooting and root cause analysis. The first objective is to identify potential sources of electrical noise throughout the complete system. The cable itself may not actually be the source. Noise could originate from a power supply, motor, PCBA, switching device, connector, or grounding point elsewhere in the equipment. Once potential noise sources are identified, they can be isolated and evaluated individually. Changes in cable routing, grounding, shielding, or component placement can then be tested to determine how they affect system performance. Robust documentation becomes extremely important during this process. Cable assembly drawings, schematics, wiring diagrams, PCBA documentation, connector specifications, and system block diagrams allow engineers to trace signals and understand grounding paths. Without accurate documentation, troubleshooting an EMI problem can become an exhausting process of trial and error. A well-documented system makes it much easier to determine what changed, reproduce a failure, and verify whether a corrective action actually solved the problem. ## The Robotics Engineer's Perspective: Look at the Real-World Installation A cable that performs well on a bench may behave differently once installed in a moving electromechanical system. Robotics and automation applications often contain motors, pumps, relays, switches, drives, and other devices capable of generating significant electrical noise. Cable routing becomes extremely important. Sensitive signal cables should be separated from known noise sources whenever the mechanical design allows it. Workmanship also matters. Improper shield termination, poor grounding, loose terminals, or incorrectly assembled connectors can reduce the effectiveness of an otherwise well-designed cable. Movement introduces another variable. A cable assembly that repeatedly flexes can experience gradual degradation of its jacket, shield, conductors, and terminations. A damaged shield, broken conductor, exposed wire, or loose connection can change the grounding characteristics of the system and introduce an EMI problem that did not exist when the equipment was new. For dynamic applications, EMI performance therefore needs to be considered alongside [bend radius](https://blog.epectec.com/high-flexibility-wires-for-minimum-bend-radius-requirements), flex life, strain relief, and cable routing. ## Designing for EMI Success From the Beginning There is no universal cable construction that eliminates EMI problems. Every application has different signals, frequencies, power levels, mechanical constraints, and surrounding noise sources. For critical applications, it is often better to begin with a robust shielding approach rather than trying to design to the absolute minimum requirement. Once testing demonstrates that the cable and system perform successfully, unnecessary complexity can potentially be removed during subsequent design iterations. Teams should also plan for at least one design iteration. Discovering an unexpected noise source during qualification testing is common, particularly during testing in an anechoic chamber where the complete system is evaluated under controlled conditions. Building time into the development schedule for testing, troubleshooting, and redesigning is far better than assuming the first cable configuration will pass every requirement. ## Summary Successful EMI and EMC performance is rarely determined by one component or one design decision. It comes from understanding how the cable assembly interacts with connectors, PCBAs, enclosures, grounding systems, nearby electrical equipment, and the physical environment in which the finished product operates. Different roles and responsibilities within an organization will tackle an EMI troubleshooting task differently. All three perspectives are valuable and may be necessary to thoroughly solve the issue(s) at hand. By defining EMI requirements early, designing the cable construction around the application, maintaining clear documentation, and planning for qualification testing and design iterations, engineering teams have a much better chance of solving EMI problems before they become expensive production or field failures. --- ## Key Takeaways - **Cable assemblies can both receive and radiate** electromagnetic interference, making shielding, grounding, and cable construction important considerations in EMI-sensitive applications. - **Braided and foil shields**, drain wires, twisted pairs, ferrites, chokes, TVS diodes, and conductive materials can all play a role in improving EMI and EMC performance. - **Radiated emissions, radiated susceptibility, conducted emissions, conducted susceptibility,** and ESD testing evaluate different ways electromagnetic interference can affect a system. - **EMI problems should be evaluated from** multiple perspectives because electrical design, documentation, workmanship, cable routing, nearby equipment, and mechanical wear can all contribute to poor performance. - **EMI-sensitive cable assemblies should be designed with** qualification testing and at least one potential design iteration in mind, especially when system requirements are critical. - [Tweet](https://twitter.com/share) Topics: [Cable Assemblies](https://blog.epectec.com/topic/cable-assemblies), [Product Design](https://blog.epectec.com/topic/product-design) --- Next | [All posts](https://blog.epectec.com/all) | [Previous](https://blog.epectec.com/avoiding-fractures-and-delamination-in-rigid-flex-and-flex-circuits) [![New Call-to-action](https://no-cache.hubspot.com/cta/default/707152/5ba29c62-2cee-436d-a029-fecba0160c98.png)](https://cta-redirect.hubspot.com/cta/redirect/707152/5ba29c62-2cee-436d-a029-fecba0160c98) ## Leave a Comment --- ## Related Posts --- ### Recent Posts --- ### Posts by Topic - [Printed Circuit Boards (162)](https://blog.epectec.com/topic/printed-circuit-boards) - [Product Design (138)](https://blog.epectec.com/topic/product-design) - [Battery Packs (122)](https://blog.epectec.com/topic/battery-packs) - [Cable Assemblies (102)](https://blog.epectec.com/topic/cable-assemblies) - [Flex & Rigid-Flex PCB's (96)](https://blog.epectec.com/topic/flex-rigid-flex-pcbs) - [Electronics Industry (61)](https://blog.epectec.com/topic/electronics-industry) - [User Interfaces (55)](https://blog.epectec.com/topic/user-interfaces) - [Quality Solutions (33)](https://blog.epectec.com/topic/quality-solutions) - [Flexible Heaters (31)](https://blog.epectec.com/topic/flexible-heaters) - [Events, Training, and Support (9)](https://blog.epectec.com/topic/events-training-and-support) - [RF Products (7)](https://blog.epectec.com/topic/rf-products) - [CNC Machining (3)](https://blog.epectec.com/topic/cnc-machining) - [Fans & Motors (1)](https://blog.epectec.com/topic/fans-motors) See All --- --- ### Need Help with A Project? 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