Selection parameters of a X & Y rated capacitors

Question

In a capacitor drop supply, X rated capacitors are responsible for dropping the AC voltage across them. I've been looking at why only X rated capacitors are used. After spending some time searching the internet, I found that X rated capacitors are connected in series (line to line) with the circuit, while Y rated capacitors are connected in parallel (line to ground).

The X rated capacitor is designed for 250, 400, 600 VAC. The effective impedance (Z), rectance (X) and the mains frequency (50 – 60 Hz) are the important parameters to be considered while selecting the capacitor. The reactance (X) of the capacitor (C) in the mains frequency (f) can be calculated using the formula:

$$ X = \frac{1}{2 \pi fC} $$

So at 0.22uF the reactance will be \$14.4k\Omega\$. Now the effective impedance can be calculated by using

$$ Z = \sqrt{R + X} $$

Now this Z is responsible for the dropping of the high voltage. So just because of high reactance (is it X rated capacitor property? Correct me if I am wrong), is it used to drop the supply voltage? What happens if we add another capacitor in series except X rated? Does the other one also work as a X rated capacitor?

Sorry SHASWAT, it's a joke referring to [motion picture ratings](https://en.wikipedia.org/wiki/X_rating). — JYelton, Aug 02 '13 at 04:44
As far as I know the X and Y designation is the letter code for the low temperature coefficient of [Class 2 ceramic capacitors](http://en.wikipedia.org/wiki/Ceramic_capacitor#Class_2). I'm not sure that alone could be classified as a capacitor "rating," hence the humor. — JYelton, Aug 02 '13 at 04:48
I found something that provide little bit of Y rated cap. http://electronics.stackexchange.com/questions/56757/why-only-500vac-rating-for-this-y-capacitor — Atom, Aug 02 '13 at 04:54
Ceramic capacitor is other thing as wikipedia says it offer high stability in case of class 1 For class 2 it offers high volumetric efficiency for decoupling, smoothing, by-pass and coupling applications. — Atom, Aug 02 '13 at 04:59
@JYelton: Yes, the "X" and "Y" in "X7R" and "Y5V" are temperature ratings for class 2 ceramic capacitors. However, I'm pretty sure the original question is about the "X" and "Y" in "Class X" and "Class Y", which are safety ratings for mains power [plastic film EMI/RFI suppression capacitors](https://en.wikipedia.org/wiki/Film_capacitor#Safety_and_EMI.2FRFI_suppression_film_capacitors) and other safety capacitors. — davidcary, Jan 04 '14 at 04:10

score 7 · Answer 1 · answered Aug 02 '13 at 05:00

7

X and Y type capacitors (as it turns out) are types of safety capacitors, usually for higher voltage. (The X and Y letter codes can also mean a low temperature coefficient for class 2 ceramic capacitors.)

Here are the relevant points from a Safety Capacitor Basics document from Tecate Group:

X Capacitors are also known as "across the line" capacitors. They are used between the "live" wires carrying incoming AC current. They're used in applications where failure of the capacitor will not lead to risk of electrical shock to the user.
Y Capacitors are also known as "line to ground" capacitors. They are used in applications where failure of the capacitor could lead to the danger of electrical shock to the user, if the ground connection is lost.

answered Aug 02 '13 at 05:00

JYelton

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So Y rated e.g can be used in EMI suppression? – Atom Aug 02 '13 at 05:02
Yes, page 2 of the linked document states "The function of these capacitors is to protect against surges and transients, as well as providing EMI filtering." – JYelton Aug 02 '13 at 05:03
So if I connect another capacitor instead of X rated cap,then it can also works as same as X rated or something else happens?? – Atom Aug 02 '13 at 05:12
Sorry SHASWAT I don't know that much about them. You might want to post that as a separate, specific question. – JYelton Aug 02 '13 at 05:16
@SHASWAT, From an eletrical function point of view these are just capacitors. From a safety point of view these are constructed to be robust and to fail safely. Capacitors not requiring safety considerations are smaller and cheaper. X and Y capacitors will have been tested to withstand certain surges / spikes and not fail in a dangerous way. – Spoon Aug 02 '13 at 07:10
Here is an informative link http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/showpage.html?&name=FOWX2.GuideInfo&ccnshorttitle=Across-the-line+Capacitors,+Antenna-coupling+Components,+Line-bypass+Components+and+Fixed+Capacitors+for+Use+in+Electronic+Equipment&objid=1073753701&cfgid=1073741824&version=versionless&parent_id=1073753700&sequence=1 – Spoon Aug 02 '13 at 07:24
@Spoon Thanks for such a good information.But this is not the answer of my question. It works but what happens if I replace the x rated with the other capacitor.. – Atom Aug 02 '13 at 08:16
@SHASWAT, In a "Perfect" world what happens is nothing. “Perfect” is a mains AC supply with no noise from other equipment on the supply or spikes caused by lightning or nearby welders and the like. However in a real application these disturbances in the supply are very large and will kill an ordinary capacitor in an interesting way. “interesting” is if you like things blowing up and making a fire and possible shock hazard. – Spoon Aug 02 '13 at 11:53
@SpoonStill not getting the exact answer of my questiona – Atom Aug 02 '13 at 12:15
@JYelton Still not getting the exact answer of my question.I already add addition information in my question that I know, but still not getting a good response. – Atom Aug 02 '13 at 12:18
@JYelton Seems like everyone is OK with your answer but they didn't get what I want to ask. – Atom Aug 02 '13 at 12:19
@SHASWAT See my earlier comment about asking a new question that's very specific. Don't post any more comments here, because it's not where users should look for answers; just accessory information about the question or answer to which it is attached. – JYelton Aug 02 '13 at 17:27
Can I use an Y2 capacitor in an application where they use an X? – JohnyTex Jan 23 '16 at 14:53

Selection parameters of a X & Y rated capacitors

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