DC- regulator - Y or X-class capacitor?

[Tantalum]

Hello

In the datasheet of an isolated DC-DC regulator module (not AC-DC!) is written that there should be a decoupling capacitor between
the grounds of both sides  (C3). The value is indicated (470pF/2kV) but not the type of capacitor.

Should it be a normal, a Y- or a X-class capacitor???

(I have read somewhere that X capacitors are for differential mode EMI and Y for common mode EMI)



Thank you

[exmadscientist]

X and Y are safety classes for capacitors that touch mains. In summary, Class Y is required for capacitors that go mains line to protective earth. Class X (or Class Y, Y can always be substituted for anything lesser) is required for mains line to line.

If you don't have mains involved, you don't need X/Y caps.

(The idea behind this is basically that lightning and giant industrial motors and rogue squirrels and basically all sorts of things are found on the mains. So mains capacitors need to be very strong to withstand that stuff. It's not about the voltages or the currents. It's about the raccoons (the pulsed, very-short-duration, single-event raccoons). No mains, no mains rating needed. But it never hurts, it's just big and expensive.)

[Tantalum]

Thank you for the explanation 

[soldar]

X Y caps

[Zero999]

What are the voltage ratings of the DC:DC converter?

It might not be for mains, but it's still possible a Y capacitor is required for C3. For example, if the input voltage is >120VDC, or the isolation voltage rating is >120VDC, a Y capacitor is required for safety reasons, just like on mains.

[Tantalum]

24VDC -> 5VDC