Not using high voltage rated Y capacitors across the isolation barrier of an SMPS DCDC module?

Dear Engineers,

We are using the THN 20-4811WI DCDC module with
Vin = 48VDC
Vout = 5VDC
Pout = 5.5W.

THN 20-4811WI
https://www.tracopower.com/int/model/thn-20-4811wi-a1

….In the application notes section (from above link) , there is a PDF called “EMI considerations”. This shows Y caps being used of voltage 2kV.

However, on our schematic, we don’t have such high voltage rated Y caps. In fact, we have a 500VDC rated capacitor across the isolation barrier, the VJ1206Y472KXEAC capacitor (4n7, 1206, 500VDC, X7R). This capacitor is not actually Y1 or Y2 rated, its just a general capacitor. Also across the isolation barrier, we have a 500V rated 1206, 1MEG resistor (ERJP08F1004V).

Incidentally, there are also three other DCDC modules across the same isolation barrier. (These are JTK3048S05 DCDC modules by XP power).

Do you think we will be OK not using such high voltage rated Y capacitors?
We are hoping that due to our 1MEG resistor across the isolation barrier....the voltage between primary and secondary will be pretty equal, so we wont need such high value rated Y capacitors?

VJ1206Y472KXEAC datasheet:
https://www.mouser.co.uk/datasheet/2/427/vjcommercialseries-1764145.pdf

ERJP08F1004V datasheet
https://docs.rs-online.com/ef78/0900766b812cb812.pdf

JTK3048S05 DCDC module
https://www.xppower.com/portals/0/pdfs/SF_JTK30.pdf

THN 20-4811WI datasheet
https://www.mouser.co.uk/datasheet/2/687/thn20wi-519375.pdf

Your input voltage is 48v,
the output voltage is 5v,

Why in the name of Michael Faraday would you need 2000v Y rated capacitors?

zenerbjt said:

However, on our schematic, we don’t have such high voltage rated Y caps. In fact, we have a 500VDC rated capacitor across the isolation barrier,

Click to expand...

Well, who designed that!
Could it be someone who has a reasonable grasp on what he is doing?
Could it be someone who does not have to go to an internet forum for guidance on the most abstruse problems that it is possible to imagine.

zenerbjt said:

In the application notes section (from above link) , there is a PDF called “EMI considerations”. This shows Y caps being used of voltage 2kV.

Click to expand...

Application notes are full of useful information, they are also intended for the guidance of wise men and the blind obedience of fools.

JimB

Why in the name of Michael Faraday would you need 2000v Y rated capacitors?

Click to expand...

Well, who designed that!
Could it be someone who has a reasonable grasp on what he is doing?

Click to expand...

Thanks, i couldnt agree with you more....so why in the attached application note are they using 2kV rated Y caps?
Presumably in case output gets connected to a non isolated mains situation.
However, there is also "charge pumping", where isolated grounds can get eventually induced up to high voltage....this can sometimes happen in power switching circuits like SMPS...even low voltage ones.
..