X and Y Capacitors - Page 1
Forum section: electronics / projects

author: skipjackrc4
author_rank: Regular Contributor
timestamp: February 05, 2013, 02:34:20 am
content: I've recently been running into designs calling for X and Y capacitors. There does not seem to be much information about these online, and none of my classes have ever mentioned them.From what I can tell, they are very robust caps for use in direct-mains connected filtering that can withstand high voltage transients. Can anybody please explain this a little better? How are the two types different?Thanks in advance!

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: February 05, 2013, 03:50:10 am
content: Wikipedia is your friend.http://en.wikipedia.org/wiki/Film_capacitor

author: ejeffrey
author_rank: Super Contributor
timestamp: February 05, 2013, 06:10:00 pm
content: They are safety ratings for use on the line side of a power supply. Most commonly they are part of the EMI suppression. Class X capacitors are certified for use in line-neutral or line-line applications and need to handle spikes present on the AC line and not catch fire in case of a fault. Class Y capacitors are used for line-ground connection, or connect primary to secondary over an isolation transformer. They need to be self healing, as faults could cause electrocution.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: February 05, 2013, 06:15:16 pm
content: Quote from: skipjackrc4 on February 05, 2013, 02:34:20 amHi ,When i was doing Vintage Repairs few months back i had access to a great resource of info on these .Cannot get the link ,Try registering in Antique radio forums and ask for help ,Someone imho there had a website dedicated to these .

author: PChi
author_rank: Frequent Contributor
timestamp: February 05, 2013, 08:17:15 pm
content: It's a while since I have worked on power supplies so I am not up to date with the details.Class X capacitors can be connected between L and N and can survive transients and never fail in such a way to cause a fire.Class Y capacitors can be connected between L , N and safety earth and are designed not to fail to cause current through earth (apart from the inevitable AC current).Try Epcos athttp://www.epcos.com/web/generator/Web/Sections/ProductCatalog/Capacitors/FilmCapacitors/PDF/PDF__EMIGeneralStandard,property=Data__en.pdf;/PDF_EMIGeneralStandard.pdf

author: PChi
author_rank: Frequent Contributor
timestamp: February 05, 2013, 08:34:04 pm
content: Apologies, Oops all I have done is repeat the information in the post by ejeffrey.

author: Kremmen
author_rank: Super Contributor
timestamp: February 05, 2013, 10:18:33 pm
content: Maybe a needless addition, but rated caps are marked so on the outside. So you must find one or more of the codes X1, X2, Y1, Y2 labeled on the component somewhere.Also, Y rated caps tend to be relatively small capacitacnce since leakage current to PE wiring is strictly limited in the code.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: February 05, 2013, 10:27:46 pm
content: So it seems that both types of caps are designed to prevent shorting? X caps can't short or they risk a fire through over current, and Y caps can't short or they expose the user to mains voltages. Is this correct?

author: ejeffrey
author_rank: Super Contributor
timestamp: February 06, 2013, 05:15:34 am
content: From what I understand, X caps are allowed to fail conducting, as long as they either melt and fuse without catching fire, or short out and blow the primary fuse.