Electronics Guide

International Standards Framework

The International Special Committee on Radio Interference (CISPR), a technical committee of the International Electrotechnical Commission (IEC), develops the primary international standards for conducted emissions. CISPR standards establish measurement methods, equipment specifications, and emission limits that serve as the foundation for regulatory requirements in Europe, Asia, and many other regions worldwide.

CISPR 32 covers multimedia equipment including computers, monitors, printers, and consumer electronics, having replaced the earlier CISPR 22 standard. CISPR 11 addresses industrial, scientific, and medical (ISM) equipment. CISPR 14-1 governs household appliances, electric tools, and similar apparatus. CISPR 15 covers electrical lighting equipment. Each standard defines limits appropriate to the equipment category and its typical operating environment.

The IEC 61000 series provides a comprehensive framework for electromagnetic compatibility that includes conducted emission requirements within its scope. IEC 61000-6-3 and 61000-6-4 provide generic emission standards for residential and industrial environments respectively, applicable when no product-specific standard exists. These generic standards reference CISPR measurement methods and limits, providing a bridge between the detailed technical requirements and the broader EMC regulatory framework.

Classification System

Conducted emission standards categorize equipment into classes based on the intended operating environment. Class A equipment is designed for use in commercial, industrial, and business environments where some level of interference can be tolerated and where professional installation may be assumed. Class B equipment is suitable for residential environments and locations where the proximity of other equipment and the expectation of interference-free operation demand more stringent limits.

Class B limits are typically 10 dB more stringent than Class A limits, reflecting the higher sensitivity of the residential electromagnetic environment. Products sold directly to consumers must generally meet Class B requirements regardless of where they might actually be used. Class A products may require warnings about potential interference and restrictions on residential use, though enforcement varies by jurisdiction.

Some standards define additional classes for specialized environments. Equipment used in light industrial environments may have intermediate requirements. Heavy industrial equipment operating in controlled electromagnetic environments may have relaxed limits accompanied by installation and placement restrictions. Medical equipment has its own classification system based on the intended use environment and the criticality of the medical function.

Frequency Ranges and Limits

Conducted emission measurements typically cover the frequency range from 150 kHz to 30 MHz, though some standards extend measurements to lower frequencies, particularly 9 kHz, for certain product categories. This frequency range captures the switching frequencies and lower harmonics of most electronic equipment while remaining below the range where radiated emission measurements become the primary concern.

Limits are specified in terms of voltage levels measured at the LISN output, expressed in dBuV (decibels referenced to one microvolt). Quasi-peak and average limits apply at each frequency within the measurement range. The quasi-peak detector provides a measurement weighted by signal repetition rate and duration, while the average detector measures the mean level over time. Both limits must be met, though they serve different purposes in assessing interference potential.

Limit curves typically show frequency-dependent values, often with different limits for frequency sub-bands. Many standards specify limits that are higher at lower frequencies and become more stringent at higher frequencies, reflecting the frequency-dependent coupling between power line noise and radio receivers. Some standards include both continuous and discontinuous emission limits, with different limits applying to steady-state and intermittent noise sources.

CISPR Standards in Detail

CISPR 32 has become the primary standard for information technology and multimedia equipment, replacing and consolidating the earlier CISPR 13 and CISPR 22 standards. It defines Class A and Class B limits for mains port conducted emissions, with measurements performed using a LISN meeting CISPR 16 specifications. The standard also addresses emissions on telecommunication ports and antenna ports, recognizing that modern equipment often includes multiple connection types.

CISPR 11 governs industrial, scientific, and medical equipment that intentionally generates or uses RF energy for purposes other than telecommunications. This includes equipment such as ISM heating devices, laboratory equipment, and medical treatment apparatus. Group 1 equipment generates RF energy incidental to its function, while Group 2 equipment intentionally generates RF energy for material processing or inspection. Different limits apply to each group, with Group 2 equipment generally allowed higher emission levels due to the functional necessity of RF generation.

CISPR 14-1 covers household appliances and similar equipment, recognizing that devices such as vacuum cleaners, power tools, and kitchen appliances contain motors and switching elements that generate conducted emissions. The standard defines limits and measurement methods appropriate to these product types, including considerations for click rate and discontinuous emissions from devices with intermittent operation.

CISPR 15 addresses lighting equipment including LED drivers, electronic ballasts, and lighting control gear. The proliferation of electronic lighting has increased the importance of this standard, as conducted emissions from lighting equipment can significantly impact the power line electromagnetic environment. Recent revisions have updated requirements to address the characteristics of modern LED lighting technology.

North American Requirements

In the United States, the Federal Communications Commission (FCC) Part 15 rules establish conducted emission requirements for unintentional radiators. Subpart B of Part 15 covers unintentional radiators, with conducted emission limits for digital devices (computing equipment) specified in Section 15.107. The FCC has historically maintained requirements similar to but not identical to CISPR standards, though efforts toward harmonization continue.

FCC requirements distinguish between Class A and Class B digital devices using criteria similar to CISPR classifications. Class B devices are marketed for use in a residential environment regardless of actual use, while Class A devices are marketed for use in a commercial, industrial, or business environment. The FCC limits are specified in dBuV measured across 50 ohms at the power mains port.

Industry Canada (now the Innovation, Science and Economic Development Canada department) enforces conducted emission requirements through the Interference-Causing Equipment Standards (ICES). ICES-003 covers information technology equipment with requirements largely harmonized with FCC Part 15 and CISPR standards. Products sold in Canada must comply with ICES requirements and bear appropriate compliance markings.

The differences between FCC, ICES, and CISPR requirements, while often minor, can create challenges for products intended for global markets. Some frequency points have different limit values, and measurement details may vary slightly. Understanding these differences and testing to the most stringent applicable requirements ensures compliance across all target markets.

European Union Requirements

The European Union implements conducted emission requirements through the EMC Directive, which requires that electronic equipment meet essential requirements for electromagnetic compatibility before it can be placed on the EU market. The directive references harmonized European standards (EN standards) that provide a presumption of conformity when followed. Most EN standards for conducted emissions are identical adoptions of the corresponding CISPR standards.

EN 55032 (adopting CISPR 32) covers multimedia equipment and is the primary conducted emission standard for IT and consumer electronics in Europe. EN 55011 (adopting CISPR 11) governs industrial, scientific, and medical equipment. EN 55014-1 (adopting CISPR 14-1) covers household appliances. EN 55015 (adopting CISPR 15) addresses lighting equipment. The EN standards include any European deviations from the base CISPR standards.

The Radio Equipment Directive (RED) applies additional requirements for equipment with radio functionality, including wireless devices and products with Bluetooth, WiFi, or cellular capabilities. While the RED primarily addresses intentional radio transmissions, it also includes EMC requirements that encompass conducted emissions. Products falling under the RED must comply with its requirements rather than the EMC Directive.

CE marking on products indicates the manufacturer's declaration of conformity with applicable EU directives including EMC requirements. The marking must be accompanied by a Declaration of Conformity document identifying the product, manufacturer, and applicable standards. Technical documentation demonstrating compliance must be maintained and made available to authorities upon request.

Product-Specific Standards

Many product categories have specific conducted emission standards that supplement or replace the generic requirements. Medical devices must comply with IEC 60601-1-2 for electromagnetic compatibility, which defines conducted emission limits based on the intended use environment and the criticality of the medical function. Professional healthcare facility environments, home healthcare environments, and special environments each have different requirements.

Automotive equipment faces conducted emission requirements defined by vehicle manufacturers and regional regulations. CISPR 25 provides measurement methods and limits for components installed in vehicles, with conducted emission measurements performed on supply lines, control lines, and communication lines. The automotive electromagnetic environment is particularly challenging due to the proximity of sensitive electronics and harsh operating conditions.

Railway and transit equipment must meet EN 50121 series standards, which define conducted emission requirements for rolling stock and trackside equipment. These standards address the unique electromagnetic environment of rail systems, including considerations for traction power systems and signaling equipment. The conducted emission limits reflect the need to protect rail signaling and communication systems from interference.

Military and aerospace equipment follows MIL-STD-461 in the United States and similar defense standards in other countries. These standards typically impose more stringent conducted emission requirements than commercial standards, with measurements extending to both lower and higher frequencies. The harsh electromagnetic environments and critical missions of military equipment justify these heightened requirements.

Measurement Methods

CISPR 16-1 specifies the measuring apparatus required for conducted emission measurements, including the characteristics of EMI receivers, LISN networks, and associated equipment. CISPR 16-2 defines the measurement methods, describing test configurations, environmental requirements, and measurement procedures. Adherence to these specifications ensures that measurements are consistent and repeatable across different test facilities.

The Line Impedance Stabilization Network (LISN) is the essential measurement device for conducted emissions testing. It presents a defined impedance to the equipment under test while coupling the RF noise to the measurement receiver. Standard LISN designs present 50 ohms between each power line and ground at frequencies above a few kilohertz, while allowing AC power to pass to the equipment. Different LISN configurations exist for single-phase and three-phase power supplies.

Quasi-peak and average detectors weight the measured signals differently, providing information about both the peak and average interference levels. The quasi-peak detector has specific charge and discharge time constants defined in the standards, designed to approximate the subjective annoyance of interference to broadcast radio reception. The average detector provides a time-averaged measurement. Both measurements must meet applicable limits for compliance.

Test configurations must follow standard requirements for cable length, equipment arrangement, and grounded reference plane placement. These details affect measurement repeatability and correlation between facilities. The equipment must operate in its most emissive configuration, which may require evaluating multiple operating modes to identify worst-case conditions.

Compliance Strategies

Achieving conducted emission compliance requires a systematic approach beginning early in the design process. Pre-compliance testing during development identifies potential problems when design changes are still relatively easy and inexpensive to implement. Full compliance testing at an accredited laboratory provides the formal documentation required for regulatory submissions.

Design for compliance incorporates conducted emission considerations from the initial concept phase. Selecting switching frequencies that place harmonics favorably relative to limit curves, allocating space and weight for input filtering, and planning power distribution architectures all influence the final emission levels. Designing with margin above minimum limit requirements provides insurance against production variations and measurement uncertainty.

When initial testing reveals emission problems, systematic troubleshooting identifies the sources and coupling paths. Separating common-mode and differential-mode emissions helps focus mitigation efforts appropriately. Comparing measured spectra to expected signatures from known sources helps identify which circuit elements are responsible. Iterative design modifications and retesting converge on a compliant solution.

Documentation of the compliance process supports regulatory submissions and ongoing production quality. Test reports, design rationale, component specifications, and manufacturing controls all contribute to demonstrating due diligence. For products under self-declaration schemes, this documentation must be maintained and made available to authorities upon request.

Global Market Access

Products intended for global markets must navigate the conducted emission requirements of multiple jurisdictions. While international harmonization efforts have reduced differences between regions, variations remain that require attention. A compliance strategy that addresses the most stringent applicable requirements provides the broadest market access with minimal additional testing.

Mutual recognition agreements between some countries allow test results from accredited laboratories in one country to be accepted by regulatory authorities in another. Understanding which agreements apply and which test data can be leveraged reduces the overall testing burden. However, product-specific certifications may still be required even when test results are recognized.

Maintaining compliance over the product lifecycle requires attention to component changes, software updates, and manufacturing variations that could affect emission levels. Change control processes should evaluate EMC implications of proposed changes. Periodic retesting may be warranted when significant changes are made to ensure continued compliance with all applicable requirements.

Summary

Conducted emission standards form a comprehensive framework that protects the electromagnetic environment while enabling the operation of electronic equipment. The standards define measurement methods, establish emission limits, and provide the regulatory basis for market access worldwide. Understanding this framework is essential for engineers designing compliant products and for organizations seeking efficient paths to global market access.

The conducted emission standards landscape continues to evolve as technology advances and new equipment categories emerge. Staying current with standards development activities and understanding how changes affect product requirements enables proactive design that anticipates future requirements. The goal remains consistent: ensuring that electronic equipment can operate without causing unacceptable interference to other systems sharing the electromagnetic environment.