When do you use high value Y capacitors?

[cupoftea]

Hi,
What are the SMPS's , where when designing them, you would use high value Y capacitors (say four 100nF Y capacitors).
....And simply not use any common mode choke at all.
(The Y capacitors being connected from chassis metal to circuit ground)

Why would you ever do this?
(Apologies, i searched but cant find docs on high value Y cap EMC performance, when no common mode choke is used)

 

[Easy peasy]

if you want to fail to meet standards for earth leakage currents.

 

[cupoftea]

Thanks, sorry i should have said, this converter feeds off isolated DC input of 5V..and gives out 24V at 90W. As such, we are not in a position to be able to inject leakage current back into the mains...if thats what was meant?

 

[Easy peasy]

for SELV circuits - there are essentially no limits on caps to earth.

 

[Calm down]

I think this should be better understood from the aspect of AC impedance. When using a larger Y capacitor, EMC is better based on the input common mode inductance. If there is no input common mode inductance, its impedance is still not small enough. Therefore, using a large capacity Y capacitor can only use a smaller input common mode inductance, but not cancel the inductance.