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Safety, Performance, and Reliability in Physical Industrial Networks

By Michael Berg

One of the benefits with Ethernet is that it has truly standardized making connections simple. At the same time, poor component selection can be a danger and risk to safety, performance, and/or reliability in industrial environments. Plans need to be made for dynamic environment conditions for Ethernet cabling just like for other wire, cable and connectors going into control panels, machines, and equipment. This discussion will examine common and pervasive environment factors such as EMI (Electromagnetic Interference) noise, strategies, and product solutions to mitigate and eliminate noise as a threat to Ethernet device performance.

EMI management best practices within the control panel

The enclosure of a control panel for a machine provides an EMI barrier protecting internal circuitry from outside noise sources. Panduit industrial Ethernet cordsets are constructed of Category 5e and 6A, industrial grade, stranded, twisted pair cable for UTP and STP installations. Each cordset is UL, NEMA, and IP rated to withstand light wash down and temporary submerged conditions without loss of performance to ensure reliability. However, EMI is also generated by the internal circuitry. The devices within the enclosures can be more at risk because of their sensitivity and proximity to these internal EMI generating sources. The controls of industrial processes reside within the enclosures, therefore additional protection is required, even though the devices are already protected from outside EMI (Figure 1).

Image of EMI noise risk within an enclosure to industrial automation systemsFigure 1: EMI noise risk within an enclosure to industrial automation systems. (Image source: Panduit)

Due to the close proximity of sensitive devices to noisy sources, the leading modes of EMI within an enclosure are capacitive and inductive coupling. Understanding both sources helps to examine how best practices and specifying noise mitigating products improve equipment reliability.

Both modes of coupling are unintentional and occur when current flowing through one wire induces a voltage on a parallel wire that lies within its magnetic field. Capacitive coupling is more of a concern in high frequency circuits, while inductive coupling is more of a concern in high current circuits. The magnitude of the noise generated can be measured with an oscilloscope with a victim wire attached (Figure 2). A multi-layered approach to mitigate EMI is recommended to maintain operations of critical communications and controls infrastructure. These layers of protection include grounding and bonding methods, wire segregation and separation, use of barriers, cable shielding, and use of filters. Panduit PanelMax™ Shielded Wiring Duct and Noise Shield route, separate, and shield sensitive wiring from noise emission. This allows pathways to be placed in closer proximity, saving valuable space within industrial control panels. The shielding provides up to a 20 dB reduction in noise (EMI/RFI), or 90% noise voltage reduction (NVR), which is equivalent to 6 inches of air spacing between sensitive and noise-emitting wiring.

Image of EMI types, sources, and mitigation practicesFigure 2: EMI types, sources, and mitigation practices. (Image source: Panduit)

The type of shielding used in the cable selected correlates with noise sources and type of noise expected in the environment.

Selecting the proper infrastructure for network communications in an industrial environment is important. One commonly asked question is ‘when and how to use shielded cabling’. Shielded cabling is often used in industrial environments to mitigate unwanted interference that finds its way into the Ethernet network cabling. Unshielded cable provides a degree of protection against interference due to the balanced twisted pair design but does not provide the same level of protection as shielded cable. This ‘electrical balance’ allows the cable to minimize the effects of EMI, the better the balance the more protection. In industrial areas where interference is abundant, the use of shielded cabling provides an added layer of protection.

What is electrical noise?

The primary application for shielded cable is environments that contain electrical noise sources near communication cabling. The environment where the cable is being installed will mostly determine whether to use shielded or unshielded cable. The ANSI/TIA-1005-A standard details the MICE rating (Mechanical/Ingress/Climatic-Chemical/Electromagnetic) system. The Panduit M.I.C.E guide is an effective tool that provides helpful guidelines for quantifying the amounts of environmental stresses like electrical noise per classification.

Reasons to use shielded cable:

  • Mandated by company specification or local area requirement - Manufacturing companies and system integrators within certain verticals have worked extensively in challenging environments for installing network cabling. This tribal knowledge of known ‘electrically noisy’ environments is best captured by documentation within company specifications and standards. It is common for these companies to include requirements and guidelines on designs and engineering documentation (best practices) for when to use shielded cable for certain applications.

    Proper design of cabling infrastructure includes avoiding electrically noisy areas as much as possible and using best practice methods, such as crossing AC lines at 90 degrees and properly grounding the shields on the shielded cable. 

  • Infrastructure is located near plant floor environment and data transmission is critical - Often, there are data transmission lines near the plant floor environment that are exposed to some level of environmental stress. Enterprise grade cable is typically not as robust as cable rated for industrial applications. Exposure to different types of chemicals, ingress of fluids, electrical noise, and flexing applications are best resolved by using industrial cable. Specifying the proper cable in the design phase will enhance the longevity and performance of the entire system.
  • Motion control and high-speed automation applications - Due to the inherently noisy environment of motion control and high-speed automation systems, many motion control vendors require or recommend shielded cable. These systems are time critical and depend on each packet of information. Even if the difference is only a matter of milliseconds, a high-speed machine can go offline, or cause damage to the equipment. In extreme cases of electrical noise from motion, control fiber optics is recommended.
  • MICE (Mechanical/Ingress/Climatic-Chemical/Electromagnetic) level of E2 or E3

Image of E2 or E3 MICE levels reflect severe levels of noise interferenceFigure 3: E2 or E3 MICE levels reflect severe levels of noise interference. The MICE rating system is an effective tool from TIA-1005 standard that provides helpful guidelines for quantifying the amounts of environmental stresses like electrical noise per classification. For more information on MICE refer to the standard or the Panduit MICE guide material found on the Panduit MICE website. (Image source: Panduit)

Electrical noise in the form of EMI and Radio Frequency Interference (RFI) are common in industrial environments. These forms of electrical noise can disturb the transmission of Ethernet network cabling. Sources of electromagnetic interference include but are not limited to: electric motors, variable frequency drives, contactors/relays, welding, fluorescent lighting, and radio communications. These devices are used in industrial environments and often affect the network cabling through inductive, magnetic, or capacitive coupling. Electrical noise can also be transmitted through common node grounds. However, extensive knowledge in these principals is not required to develop a well-designed physical infrastructure. Physical separation with air space and/or isolation barriers is effective, but at certain points Ethernet network cabling is still exposed to the noise hazard. Determining the source of the noise in a control system can be difficult and require significant amount of test equipment and time. Therefore, following best practices in the design of the physical infrastructure saves valuable time and resources while guaranteeing better performance. Ground and bonding systems are integral parts of Ethernet communication infrastructure, but it is not an absolute science. Each application has its own unique environmental noise and grounding situations that require best practices and experience to understand. Improper grounding and bonding can conduct noise that disrupts the transmission of the Ethernet packets.

For more information on shielded applications, visit Panduit’s industrial environment application guide, or download the Noise Mitigation for Control Panels white paper. For more information on MICE guidelines, visit the Panduit MICE landing page.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Michael Berg

Michael Berg is a Sr. Business Development Manager for Industrial Network Infrastructure for Panduit Corp, a global leader in network and electrical infrastructure solutions based in Tinley Park, Illinois. In this position Michael is responsible for channel business development and programs for Industrial and Manufacturing markets.

Michael has been with Panduit for 30 years and has experience ranging from research and development, product management, marketing and solutions marketing and business development. Michael has expertise in industrial networking and infrastructure solutions, control panel solutions and partnering programs. Michael is a graduate of University of Illinois at Chicago, with a BS in Marketing.