Combatting the Effects of EMI with EMC Design Principles for Electrical Panels
EMC-compliant panels are an excellent first step in reducing electromagnetic interference from industrial control systems. Learn about some features of electromagnetic compatibility in panels.
One way to restrict electromagnetic disturbance's adverse effects is by designing electromagnetic compatibility (EMC)-compliant panels. It means designing boards, installing electronic components, routing wiring, and following best practices to minimize the impact of electromagnetic disturbance within electrical panels. While EMI is the interference resulting from electrical disturbance, EMC is the compatibility products, and assemblies offer to block or mitigate these harmful effects.
Figure 1. Designing an EMC-compliant panel restricts electromagnetic disturbance's adverse effects. Image used courtesy of Adobe Stock
An EMC-compliant panel can operate in a highly electromagnetically polluted area, as many industrial environments are known to be, minimizing its effects on the electrical components and keeping the overall functionality in the design characteristics.
Advantages of EMC Compliance
When an electrical panel is designed following proper EMC practices and directives, it provides the system and personnel with several advantages.
EMI Prevention From the Beginning
The EMC-compliant panel helps limit electromagnetic interference from the initial system design phase. It prevents efforts at the later stages of live testing and operation, including both cumbersome and time-consuming panel redesigning and component replacement. Nobody wants to commission a system to discover that many challenges have been accidentally overlooked.
Protecting Low Voltage Signal Integrity
EMC-compliant panels also help to protect low-level signal information in process industries. Low-level signals, such as 0-10 V or 4-20 mA analog sensor outputs, are highly susceptible to EMI and can alter the original information in these signals—this is sometimes referred to as electrical ‘noise’.
An EMC-compliant panel prevents the effects of EM interference on these signals and retains the original information. There are additional EMI protection steps for many of these analog signals, but a properly designed panel is an excellent first step.
Compatibility with Regulations
Making your panel EMC compliant helps your organization get the accreditation status of various standardization and compliance bodies. Accreditation also helps improve market share, enhanced customer trust, and, most importantly, safety, reliability, and trust in an organization's products and services.
Following are some standards for EMC-compliant panels.
This directive is related to Europe and requires all panel manufacturers that intend to sell their products (of which EM interference is unavoidable) in the European market. The main aim of this directive is to prevent EM interference from disturbing the performance and operation of other equipment and systems.
The International Electrotechnical Commission – IEC standard 61000-5-2 deals with earthing (earth grounding) of the electrical panel. This standard is used for products other than power stations and substations.
This IEC standard complements the previously listed standard and deals specifically with EM interference for electrical panels used in powerhouses and substations.
Figure 2. There are several design considerations when it comes to designing a panel for EMC compliance. Image used courtesy of Adobe Stock
Panel Design for EMC Compliance
Let's look at some features of the panel that make it compliant for use in an EMI environment.
Panel Construction Materials
The control panel should be constructed of conductive material to minimize electromagnetic interference effects. Non-conductive parts or insulating material create an impedance effect, facilitating the propagation of EMI.
Take special care in isolated areas, such as small partitions and door hinges inside the panel, and make sure these parts are also constructed of conductive material. Additionally, the panel should not be coated with non-conductive, insulated material or painting that restricts conduction in any form.
Placement of Components
Install the components inside an electrical panel, so they do not affect each other. It can be achieved by separately installing components that emit or are affected by EMI. If creating a physical distance between such components is impossible, use a separate metallic enclosure to prevent EMI.
Use shielded cables for small analog and communication signals because these signals are sensitive to EMI. Shielding can consist of a braid, metal strap, or a combination.
Use shield support inside the panel for placing the cable. This helps in the good planar connection between wires and board. Additionally, clamp the shielded cable with the shield clamps or cable ties.
Do not use excessive wiring, and keep the wiring as short as possible. Long wires, or improperly terminated wires, can easily receive and amplify EMI signals, much like an antenna.
Make sure to keep the shield and unshielded wiring separate from each other—also, route high-power cables separately from low-power cables. Similarly, power cables for VFD must follow a separate route from their (motor) output cables.
Use separate ducts or conduits for routing the wiring of different zones.
Figure 3. By taking certain steps in panel design, the harmful effects of EMI can be mitigated in existing and future facilities. Image used courtesy of Adobe Stock
Line Filters and Reactors
Line filters and reactors prevent interference from common sources such as variable speed drives and DC power supplies. Such devices, creating induction and high-frequency switching, create interference that influences nearby components or cables carrying electronic signals.
To use filters, install them at the disturbed line, with a minimum distance from the source. Consult the filter manufacturer or documentation for appropriate filter specifications since many construction methods and models are intended for various situations.
Wires left disconnected from the earth can collect high-frequency radiation and create electrical or electronic component disturbances. This effect can be negated by appropriately using the earthing system.
When appropriate, the entire panel must be properly grounded according to best practices or standards. Small, isolated parts must also be appropriately connected to the earth terminal.
The shielded terminals must also be grounded with a clamp fastened to the earth terminal strip or panel's earthing plate. Metallic cable trays must also be connected to the earth system.
Creating a system free of any interference is almost impossible. Still, many steps can be taken from the beginning of the design phase to mitigate harmful effects from EMI sources, both existing in a facility and installed in the future.