Uninterruptible power supply (UPS), as a constant frequency, stable voltage, pure, and uninterrupted high-quality power supply, is widely used in various places with high requirements for power quality and continuity, such as personal, commercial, light industry, and industrial areas. When selecting UPS for various scenarios mentioned above, the core focus is mainly on factors such as load capacity, load characteristics, and power grid system. Generally, it is customary to ignore whether the EMC category of UPS matches the on-site application environment.

Electromagnetic compatibility performance (EMC) of UPS
Performance that encompasses two aspects

1.EMI: Electromagnetic Interference, also known as electromagnetic interference, refers to theelectromagnetic waves generated by UPS equipment during its own operation, which are emittedexternally and cause interference to other parts of the equipment or external devices.

2.EMS: Electromagnetic Susceptibility, which refers to the sensitivity of UPS equipment toexternal electromagnetic interference.

Simply put, we compare UPS to humans and electromagnetic interference (EMI) to cold viruses, with sensitivity (EMS) being the susceptibility to colds. If the virus is not easily transmitted, it indicates good protection or good physical fitness; If you are not prone to catching a cold, it indicates strong immunity, which is the English word 'immunity', which means strong resistance to electromagnetic interference.

However, in many practical cases, due to the incompatibility between the EMC of UPS and the on-site electromagnetic environment, operational abnormalities and risks have become common. For example:

A customer installed UPS near a large capacity transformer, causing short-term output interruption when the UPS switches between dual change mode and battery mode.

Some customers installed UPS around the speaker amplifier in the venue, causing abnormal phenomena such as intermittent high-frequency noise during speaker operation. Tracing back to the source, these are all caused by the mismatch between UPS's EMC performance and the surrounding environment.

Applicable environment, EMC category and matching of UPS

EMC Applicable Environment Division

According to GB7260.2-2009/IEC 62040-2:2005, based on the EMC indicators of different UPS application environments, the environments used by UPS are divided into two categories according to EMC requirements.

● Category 1 environment: residential, commercial, and light industrial areas directly connected to public low-voltage power supply systems without intermediate transformers.

● Category 2 environment: All commercial, light industrial, and industrial areas that are not directly connected to low-voltage power supply systems for residential buildings.

Incorporate the above standard provisions

Translate into more complete and clear content

The first type of application environment mainly refers to the application environment where UPS is directly connected to the public low-voltage power grid on the input side without an intermediate transformer. Typical application scenarios include residential communities, small and medium-sized commercial office buildings, commercial and residential buildings, commercial buildings without independent substation transformer power supply, small factories, etc.

The second type of application environment mainly refers to the installation of an intermediate transformer between UPS and the public low-voltage power grid. In this scenario, UPS is not directly connected to the public low-voltage power grid. Typical application scenarios include: medium to large industrial enterprises, data centers, medium to large commercial complexes, hospitals, etc.

In the first scenario, other electrical/electronic information equipment installed by the customer in the location is usually more susceptible to EMI interference generated by UPS operation compared to the second scenario, which mainly includes:

Conducted disturbance (CE): During normal operation, UPS will cause disturbance to the power grid through the power line. If there is a high amplitude conducted disturbance at the UPS power terminal, it may cause interference to IT, communication and other equipment in the same power grid, resulting in abnormal situations such as data loss.

● Radiation Disturbance (RE): During normal operation of UPS, due to the influence of internal nonlinear devices and parasitic capacitors, UPS as an interference source will emit radiation disturbance into the surrounding space, which may affect the normal operation of surrounding high sensitivity electrical appliances.

☑ Therefore, in the first scenario, the EMI emission index requirements for the applied UPS will be relatively strict, in order to minimize the impact on other devices as much as possible.

EMC Classification of UPS

According to the different applicable environments of UPS, GB7260.2-2009/IEC 62040-2:2005 divides UPS into four levels based on EMC indicators: C1/C2/C3/C4. Users can generally obtain UPS EMC levels through UPS product manuals and other materials

UPS with different EMC levels

Suitable for different EMC environments, specific instructions are shown in the table below

EMC categories, indicators, and applicable environments of UPS

☑ UPS with EMC type C1 can be used in Class 1 environments without any restrictions, such as personal home office, NAS system, small office commercial, etc.

☑ UPS with EMC type C2

☑ UPS with EMC type C2 is allowed to be used in Class 1 environments such as homes and personal offices when using qualified connectors that comply with national standards (such as GB1002) or IEC standards (such as IEC309) for connection, or when using permanent connections (such as welding, riveting, etc.). However, additional measures must be taken to reduce EMI interference of UPS based on the actual situation on site, such as:

1. Depending on the length of the cable and the connecting equipment, use shielded cables.

2. Increase measures such as filters and surge protectors depending on the quality of the power grid.

In summary, C2 type devices are not recommended for direct use in homes and personal offices without preparation. Due to the RF interference of this type of UPS, it may affect the normal operation of other devices for users in Class 1 environments.

Therefore, the standard requires manufacturers to include the potential risks mentioned above as a warning: "Warning: This product is a C2 UPS and may require installation restrictions or additional measures to suppress radio frequency interference for residential areas." Write it into the product manual.

☑ UPS with EMC type C3 is allowed to be used in Class 2 environments with restrictions (such as shopping malls and industrial production enterprises that are more than 30m away from residential buildings and powered by independent substation transformers).
This type of UPS may have installation restrictions or require additional measures to prevent the RF impact of the UPS on other devices in the installation site. Manufacturers need to include the potential risks mentioned above as a warning: "Warning: This product is intended for commercial and industrial use in Class 2 environments and may require installation restrictions or additional measures to suppress interference." Write it into the product manual.