Clarification of AC, X & Y Capacitors *Solved* - Page 1
Forum section: electronics / beginners

author: t1d
author_rank: Super Contributor
timestamp: October 06, 2019, 03:31:19 am
content: I have always heard that if you need a capacitor for AC, you need a X (High-side,) or Y (Low-side) class capacitor. So, I am wanting to stock some 10uF AC caps, for general purposes. I go to Mouser and start to search, but I can't find a way to specify X rated caps. I find Film Capacitors that have an AC and DC voltage rating. I find "Safety Caps," but I don't know what makes them special. I wonder if Safety Caps are the X and Y caps, but I don't see a way to search by X and/or Y perimeters. Bi-Polar caps don't seem to have an AC rating.I would search this out myself, but I just don't know the terminology to search by. So, where to begin?If you could make it specific to searching on Mouser, that would be better, because that is where I normal buy components. Please point me in the correct direction...Thank you very much for your help...

author: bdunham7
author_rank: Super Contributor
timestamp: October 06, 2019, 04:07:28 am
content: The short version is the what you are referring to as 'safety caps' are small value snubbers, designed to suppress switch noise and RF noise, that are placed on the line voltage section of a device. X caps are suitable for line-to-line or line-to neutral, Y caps are suitable for line-to-ground. The ratings are not exclusive and capacitors can have both an X and Y rating--they'll be rated for a maximum voltage and either X, Y or both.Other than that specific application, most capacitors are NOT X or Y rated. I've never seen a 10uF X or Y cap, they are typically much smaller. You don't need or want X/Y caps for general purpose AC applications. Can you give us an example of where you might want to use the capacitors you want to stock?

author: not1xor1
author_rank: Frequent Contributor
timestamp: October 06, 2019, 05:00:14 am
content: this pdfprovides some hints about the difference between X and Y capacitors and the purpose of high capacity value X2 capacitors

author: MagicSmoker
author_rank: Super Contributor
timestamp: October 06, 2019, 12:44:26 pm
content: There's lots of confusion about this. X capacitors are safety-agency approved to go from Line to Line or Line to Neutral and can fail short or open because a fuse is presumed to be present. There is no restriction on the value and you can, indeed, buy X-rated <rimshot!> capacitors with absurdly large values of 10uF. In fact, in industrial equipment this value is not uncommon given the extreme levels of noise present.Y-capacitors go between either Line or Neutral and Earth Ground so they are considered much more dangerous from a safety standpoint and are therefore highly restricted in value (based on the amount of current they shunt into Earth Ground) and they must always fail open. Y-capacitors can be used in both locations - that is, X or Y - but the range of values vs. RMS voltage rating is much more limited.The capacitor often seen bridging input and output common on a transformer must also be Y-rated, as it's failure would defeat the isolation provided by the transformer.

author: t1d
author_rank: Super Contributor
timestamp: October 07, 2019, 06:01:47 am
content: Thank you all for your replies.I see that AC-side caps can be dangerous. So, I have more to learn before buying them. I usually only work with DC. But, I guess my question still stands as to how to search for them on Mouser, if I ever need to buy such...I appreciate all of you.

author: Zero999
author_rank: Super Contributor
timestamp: October 07, 2019, 08:29:57 am
content: The search features on parts distributor sites are far from perfect. Mouser is generally quite good, but there doesn't seem to be a way to filter for Y1, Y2, Y3, X1 , X1 etc. Your best bet is to look in the safety capacitors section.https://www.mouser.co.uk/Passive-Components/Capacitors/Safety-Capacitors/_/N-fb8xlDigikey have better search filters: click on "More Filters", then "Ratings".https://www.digikey.co.uk/products/en/capacitors/ceramic-capacitors/60https://www.digikey.co.uk/products/en/capacitors/film-capacitors/62

author: t1d
author_rank: Super Contributor
timestamp: October 07, 2019, 09:12:50 am
content: Quote from: Zero999 on October 07, 2019, 08:29:57 amThank you! Now, I don't feel so dumb. <g>I'll mark the thread as "Solved."