I have an two inline (EMI) filters. One with the rating (as given in datasheet):


A. @ 115 VAC 60Hz............................0.20 mA MAX

B. @ 250 VAC 50Hz.............................0.40 mA MAX

And another one with the following details:

0.8mA MAX 250V,50HZ

Are they same when it comes to leakage current as a parameter ? What I am understanding here is that since in first one EACH LINE TO GROUND LEAKAGE CURRENT IS 0.4 mA it will sum up to 0.8mA for both. I am an Electronics person and Electrical bounces a little above my head. Kindly help.

  • \$\begingroup\$ How many lines do you have? Each device only connects to one surely? \$\endgroup\$ – Solar Mike Jul 29 '17 at 7:02
  • 3
    \$\begingroup\$ The safety AC leakage globally for consumer goods =0.25 mA which defines the precise pair(s) of Y caps to Earth Gnd at line f and V from net impedance which are effectively a differential LC "PI" filter for ingress & egress noise. More current means more attenuation and more AC leakage reactance. In practice if the same caps are used at twice the voltage and same frequency, the current doubles but at 50 Hz slightly less. (5/6) . For industrial goods with multiple supplies, in North America I know it is 2.5mA per system. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 29 '17 at 7:09

enter image description here

Figure 1. A mains filter. Notice the two Y capacitors. Source: Elliot Sound Systems.

  • The current through the Y capacitors will be proportional to the voltage across them.
  • Note that the left CY is between neutral and earth while the right one is between live and earth.
  • Since the neutral is "neutralised" by bonding it to earth at the local transformer or building meter point there should be no voltage difference between N and E. Hence there should be no current in the N-E capacitor.
  • Both capacitors are required in case of L-N reversal due to use of non-polarised plugs or mis-wiring. The neutral capacitor may also be required to shunt high frequency harmonics or noise to earth as L1 will tend to block them.

Are they same when it comes to leakage current as a parameter?


  • \$\begingroup\$ in theory earth ground is 0 ohms wrt. N but , in practise it is much higher than neutral copper impedance to remote transformer earth ground unless locally earthed to underground metallic plumbing., so both caps form a differential filter and lower emissions by RF impedance shunt to local residential ground at outlet. N-E voltage may be as high as 10% line V at rated Service current. So N is not "neutralized" (-1 technical error) for AC current. It's impedance may be 1 to 100 Ohms depending on soil conditions, or less if locally earthed. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 29 '17 at 15:04
  • \$\begingroup\$ Thanks, Tony. I'm aware of that and my answer pointed out that the neutralising is done remotely. My main point still stands that the N capacitor will not pass the same current as the L capacitor: at 10% of line V it will be 10% (or to be correct, 1/9) of the L capacitor current (since the L would be at 90% of line V). \$\endgroup\$ – Transistor Jul 29 '17 at 15:10
  • \$\begingroup\$ For safety at 50/60Hz yes, but the whole purpose is for RF where it is more equal due to line inductance thus it is a differential LPF. ( in both directions, for conducted and possibly radiated noise.) so the Neutral to ground resistance is important for reducing common mode noise leakage to humans but also important for unwanted EMI \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 29 '17 at 15:52
  • \$\begingroup\$ Agreed. But the OP's question was about spec. for the mains current leakage. I think we've got it covered. Thanks. \$\endgroup\$ – Transistor Jul 29 '17 at 15:55
  • \$\begingroup\$ the main thing is that 0.4mA & 0.8mA exceeds consumer specs if using 230V/Hz but will work. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 29 '17 at 15:56

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