What to Know About Conducted Emissions Limits

Key Takeaways

• What are conducted emissions?

• Conducted emissions limits

• The CISPR 11 and EN 55011 standards

Devices are subjected to EMC testing to identify the level of conducted emissions coming from them

Most electronic circuits inherently produce electromagnetic interference (EMI). The EMI generated can be either conducted emissions or radiated emissions, both of which interfere with the internal components in equipment or devices (or those in close proximity) and affect their normal operations.

To prevent maloperation from electromagnetic interference, international regulatory bodies set conducted emissions and radiated emissions limits. Equipment on the electronics market must satisfy these regulations and are considered electromagnetically compatible for doing so. In this article, we will discuss various international regulatory standards and the conducted emissions limits set by them. 

What Are Conducted Emissions?

Electromagnetic energy that gets coupled into electrical or electronic devices, power cables, or associated circuits is called conducted emission. Conducted emissions can be further classified as common-mode interference or differential-mode interference. 

Common-Mode Interference

Common-mode interference appears in live wires, neutral wires, or signal wires with respect to the earth connections. Signal and control lines are the main victims of common-mode conducted emissions. 

Differential-Mode Interference

When the interference is between the live wire and neutral wire or between signal wires, it forms differential-mode conducted emissions. Common-mode conducted interference is normally associated with high-frequency switching, whereas differential-mode conducted emissions results from low-frequency switching.

Conducted Emissions Limits

There are several agencies that issue conducted emissions limits on various equipment such as consumer electronics, telecommunication systems, information technology systems, and medical equipment.

The International Electrotechnical Commission (IEC) is a renowned regulatory body that sets generic EMC standards for equipment or systems in residential, industrial, and commercial environments. CISPR is another governing body that regulates the conducted emissions and radiated emissions produced by electronic products in order to make them electromagnetically compatible. The Federal Communication Commission (FCC) and European Standards (EN) are technical regulatory bodies that draft the conducted emissions limits in industrial, scientific, communication, automotive, medical, and consumer devices.

These devices are subjected to EMC testing to identify the conducted emissions from them. If the conducted emissions are within the acceptable limits presented in the standards that are applicable to that particular region, the device is considered immune to conducted EMI.

The upcoming section discusses the conducted emissions in devices and equipment under the CISPR 11 standard and EN55011 standard. 

The CISPR 11 Standard 

CISPR 11 is the most widely used EMC standard in Europe. It is drafted by CISPR: The International Special Committee on Radio Interference, which regulates the electromagnetic emissions from industrial, scientific, and medical equipment. CISPR standards categorize ISM equipment into two classes, which are further classified into two groups.

• Class A: Equipment that is suitable to use under any establishment other than a residential building.
• Class B: Equipment that is used for residential applications.

The two classes are further divided into:

• Group 1: ISM equipment that only uses RF energy for the internal functioning of the equipment.
• Group 2: ISM equipment that is used for external treatment and other processes.

The table below shows the conducted emissions limits in dBuV (quasi-peak and average value) for the frequency range of 150kHz to 30 MHz:

The EN 55011 Standard

EN 55011 is an EMC standard drafted by the European Committee for Electrotechnical Standardization. Similar to CISPR 11, the EN 55011 standard sets the electromagnetic disturbance limits on ISM equipment. It also covers arc welding equipment and electro-discharge machines. EN 55011 is the emissions standard that considers both conducted and radiated emissions in ISM, excluding the equipment in the field of telecommunications. 

Cadence software can help you design ISM equipment that satisfies the conducted and radiated emissions limits set by regulatory bodies such as CISPR 11 or EN 55011. Subscribe to our newsletter for the latest updates. If you’re looking to learn more about how Cadence has the solution for you, talk to our team of experts.