Y-cap in offline SMPS: Leakage prevents high voltage?

[eem2am]

Hello

The secondary ground of an offline SMPS can flot up to dangerously high voltages.

Is part of the reason for the Y-Cap, so that floating up to such a high voltage doesn't occur.................because the leakage current through the Y Cap will stop the secondary ground from floating up to such a high voltage?

 

[FvM]

The secondary ground of an offline SMPS can flot up to dangerously high voltages.

Why? An dangerous in which sense?

Is part of the reason for the Y-Cap, so that floating up to such a high voltage doesn't occur.................because the leakage current through the Y Cap will stop the secondary ground from floating up to such a high voltage?

Y-caps are provided for EMI supression. I dont expect, that you'll be able to measure a significant leakage with these high quality capacitors.

There's in fact a risk, that electrostatic voltages across the isolation boundary (and the Y-cap) causes a discharge at an unwanted place, e.g. damaging an opto coupler. Offline SMPS with profound design have probably a spark gap designed into the PCB, preferably as a milled air gap, to force the discharge to occur at this place.

A high-ohmic resistor in parallel to the Y-cap is another means to prevent static charges to build up.

 

[eem2am]

supposing that such a high-ohmic resistor was not fitted in parallel with the y capacitor.....then would anyone touching the secondary side be likely to receive a shock?