What is the difference between Class A and Class B in electromagnetic compatibility?

Electromagnetic Compatibility (EMC) refers to the ability of electronic equipment to operate normally in an electromagnetic environment without causing interference to other surrounding devices or the environment, and also without being affected by external electromagnetic interference. In the industrial field, electromagnetic compatibility is generally divided into two grades, namely Class A and Class B. The following is a detailed introduction to both: 

1.The difference in applicable environments 

Class A:

Applicable to commercial, industrial and professional environments. Such equipment is typically used in office buildings, factories, enterprises, data centers, laboratories, etc.

Class A devices usually encounter higher levels of electromagnetic noise, so they need stronger anti-interference capabilities in their design.

Class B:

Applicable to home and light commercial environments. Such equipment is typically used in homes, residences, and ordinary office environments.

The operators in the working environment of Class B devices are non-professionals, and there are various low-voltage electronic products with relatively weak anti-interference capabilities. The tolerance for electromagnetic interference in such environments is low, and the devices need higher electromagnetic compatibility to ensure they do not cause interference to other electronic devices or broadcasting services. Therefore, the control of EMI electromagnetic emissions is more strict.

2. Differences in Electromagnetic Interference Limits (EMI) 

Class A:

For Class A devices, the limits on electromagnetic radiation are relatively high, allowing these devices to generate more electromagnetic radiation. However, since these devices mainly operate in industrial and commercial environments, their radiation has a relatively small impact on the outside world. The radiation limit for Class A is higher than that for Class B, allowing for more electromagnetic radiation, but still meeting the basic requirements of electromagnetic compatibility.

Class B:

For Class B devices, the limits on electromagnetic radiation are lower, meaning they must control radiation more strictly than Class A devices. Class B devices are mainly used in home and light commercial environments, so they must minimize electromagnetic interference with the surrounding environment, especially as the requirements for electromagnetic compatibility are stricter in home environments. The radiation limit for Class B is lower than that for Class A to ensure that the devices do not interfere with household appliances, televisions, radios, and other home devices.

3. Differences in Equipment's Anti-interference Capability (EMS) 

Class A:

Class A devices are designed to withstand strong electromagnetic interference. They are usually exposed to more electromagnetic noise (from industrial equipment, large motors, frequency converters, etc.), so they have higher requirements for resistance to electromagnetic interference.

These devices need to have strong common-mode interference resistance to ensure stable operation in high-noise environments.

Class B:

The working environment of Class B devices is relatively clean, with less electromagnetic interference, so their anti-interference requirements are relatively lower.

Nevertheless, Class B devices still need to have a certain anti-interference capability to prevent external electromagnetic waves from affecting the equipment.

4. Testing and Standards 

Both Class A and Class B devices need to pass EMC tests, including radiation emission and conducted emission tests. The requirements of the standards are as follows:

Class A: Applicable to devices in commercial environments, which pass the Class A standard test. The radiation limit is higher and the conducted noise limit is more lenient.

Class B: Applicable to devices in home environments, which pass the Class B standard test. The requirements for the radiation limit are stricter and the conducted noise limit is also stricter.

Common related standards include: 

The European EMC Directive (2014/30/EU) and EN 55032, EN 60601-1-2, the FCC Part 15 in the United States, and the Chinese standards GB 9254 and GB 4824 all have their own requirements for radiation limits and conducted noise limits for Class A and Class B.