Y2 capacitors for mains isolation

[AndrewT]

Originally Posted by bogey_golf

I've included a *rtf file with an excerpt from the UL 60950-1 standard that should be a bit more comprehensive.

having read that rtf, I now know why I said I was not competent to advise on Class1 (double insulated) equipment.

[Joskij]

Hello! Sorry, little hard to read this all, I'm from Russia. I'm a manager, we sell components from China. And now I have a problem - customer wont to use X1/Y2 Murata SMD capacitor, and ask me, he can use one capacitor, or need use two ( serial connection )
What different? Virtual ground ?
This capacitor support 2KV AC, 60sec. If single, or need use two ?

[richie00boy]

It is not recommended by manufacturers to connect caps in series to obtain higher voltage ratings, I think it is actually not permitted in safety regulations as well. This is because it can be difficult to guarantee the voltage across them.

Sorry but I don't quite understand what you are asking. Where does he want to connect capacitors?

[carz]

Originally Posted by star882

Over 90% of the switching wall warts have them. The main exceptions are the really small ones.
They are also common in internal power supplies. Here's a digital TV receiver with an internal power supply. The Y2 capacitors are blue and note that the receiver is not grounded.
Looking in the top of the Zenith DTT900 after taking the top of the box off. The power supply is on the right, and the main...
Detail of the top of the power supply PCB in the Zenith DTT900.

The circuit ground is connected to the casing right ? Is it safe to connect the casing to the electrical ground / earth ? Are there any reasons that i should know why this should not be done ?

It is also very common to find the signal ground to be connected to the casing for DVD players. And these DVD players with SMPS power supply also have the Y2 capacitors. That's why you sometimes get a mild shock when touching the casing.

Does anyone know why these DVD players manufacturers almost always never connect the casing to a power supply ground ?

[AndrewT]

Originally Posted by carz

Does anyone know why these DVD players manufacturers almost always never connect the casing to a power supply ground ?

Probably because they are designed, manufactured and tested to comply with Double Insulated regulations (ClassII equipment).

Although I have doubts about the "designed and tested" compliance part for the very cheap items coming from the Far East.