What is the impact of the grounding resistance of the edge box on EMC performance?

The grounding resistance of the edge computing box directly determines the high-frequency noise discharge efficiency and the ground potential difference. When the grounding resistance is <0.1Ω, it can ensure that ESD and EFT surge energy flows quickly into the ground and protects the devices from damage. When the grounding resistance is >1Ω, it will cause the common-mode voltage to rise, causing interface overvoltage or reset. Common defects include a tingling sensation when touching the casing and prominent common-mode spikes in conducted radiation tests. Improvement measures include using a copper braided strip with a width of 15mm and a length <0.5m to connect the casing and the grounding copper busbar. The surface of the braid is tin-plated and pressed firmly. A ferrite magnetic ring CMZ7060A-701T is placed on the grounding wire. Its name is CM common-mode Z impedance 7060, size 7.0×6.0mm, and 701T impedance 700Ω. It suppresses high-frequency resonance of the ground wire at 100MHz. At the same time, the internal protective ground (PE) and digital ground are connected at a single point through a 1nF 2kV Y capacitor to provide a high-frequency loop. After the measured grounding resistance was reduced from 0.5Ω to 0.05Ω, the edge box showed no reset in the 4kV EFT test and a 6dB margin in radiated emissions. It can be seen that low-resistance grounding is the cornerstone of EMC.