Leakage current is an important parameter of power line filters

People often have a negative attitude towards this concept that is not worth mentioning. Leakage current is not a function of component quality, but it is a direct function of the capacitance value to ground. The larger the capacitance value, the smaller the impedance to common mode current, and the greater the suppression of common mode interference. Therefore, leakage current is an indicator of filter performance, the higher the better.

Why do security agencies need to establish leakage current standards? This is to limit the expected ground return current value. The line to ground capacitor provides a channel for 50Hz/60Hz current to flow to the casing. As long as the equipment is grounded, these currents will flow in the grounding circuit without causing any danger. However, even if the grounding circuit is reliable, there is a very small probability of failure, and communication in this case may be through the human body. To avoid this situation, the leakage current parameter must be limited, and the grounding return current should be limited to a safe value, typically 0.5 to 5mA.

Due to the fact that the majority of leakage current comes from power line filters, caution should be exercised when setting leakage current limits for the filters themselves. There is a tendency in industry to specify a minimum leakage current to comply with all safety regulations, typically 0.5mA. This regulation should not be arbitrarily decided, as allowing a larger leakage current may reduce the cost and shape of the filter.

Note that the leakage current is directly proportional to the line voltage and frequency. Therefore, it is not wise to specify an operating frequency greater than 60Hz when the leakage current limit must be met.