Can Y-Cap Remove DC Offset between Grounds?

Question

I ask this question because I saw this in an Altium article:

---

In power systems, be careful how you use a capacitor to ground to ensure a consistent ground reference. Y-rated capacitors are best in this application, where you need to remove DC offsets between planes while still providing galvanic isolation and high-frequency EMI filtering.

---

As far as I know, capacitors block DC current and there is usually a non-zero DC voltage between a general ceramic capacitor. Y-caps are specially designed for safety purposes. It is placed between live and earth and is open when fails.

My questions are:

1. Is practical Y-rated capacitor such a special capacitor that can even set two isolated ground references to the same DC voltage?
2. I think 'remove DC offset' means having the same DC voltage. Do I understand 'remove DC offset' correctly?

(Here is a similar question but I cannot get a exact answer)

Answer 1

No, the wording is bad. Capacitors or Y capacitors do not remove DC offsets by making the DC voltage same over the capacitor

Capacitors specifically allow an DC offset so you are free to define the DC voltage over the capacitor, which also allows you to set or remove DC offset between two circuits, so basically, they allow two circuits to be at different DC offsets.

So since one side of the capacitor can be at different DC offset than the other, in common language it can be said that the capacitor removes DC offset, so that DC offset of some circuit does not affect the DC offset of the other circuit.

Which makes both your questions have incorrect assumptions.

1. Y capacitors are like any normal capacitor but just rated and guaranteed for handling mains voltage and even more and fail safely open in a fault situation. Y capacitors are used to keep DC voltage difference but allow AC voltage waveforms to be equal on both sides, i.e. EMI reasons.

2. As explained, no

Answer 2

Y-rated capacitors are best in this application, where you need to remove DC offsets between planes while still providing galvanic isolation and high-frequency EMI filtering.

My primary language is not English but what I understand from "removing DC offset between grounds" is to bring them to the same DC potential.

Now the bolded statement above makes no sense to me because if a Y-cap was used to "remove" the DC offset between grounds then they wouldn't be isolated. If we want to remove the DC offset between grounds then why would we use a Y-cap? We would short them instead!

This makes my answer to both of your question "No".