How can the safety capacitors of a concentrator be designed to ensure EMC compliance?

The safety capacitors (X and Y capacitors) in the concentrator provide filtering, but their leakage current can affect metering accuracy and personal safety, requiring a balance between EMC and safety regulations. The X capacitor (differential mode filter) uses a metallized polypropylene film capacitor (CBB) with a capacitance of 0.1-0.47μF, which contributes significantly to EMC with minimal impact on metering. The challenge with the Y capacitor (common mode filter) lies in its leakage current; a Y1-class capacitor with low leakage current (e.g., 2.2nF, leakage current <0.25mA) must be selected.

To reduce the impact of Y capacitor leakage current on the sampling ground, the Y capacitor's grounding terminal is directly connected to the chassis ground (PE), rather than the circuit ground. If the circuit ground needs to be connected to the chassis ground, it can be done by connecting a 100kΩ resistor in parallel with a CMZ2012A-900T common mode inductor. The safety capacitors must be certified (e.g., UL, CQC) and meet the rated voltage and pulse withstand voltage requirements. This design ensures effective filtering, meets the EN 55032 standard, and keeps leakage current within a safe range.