Safety capacitor comparison query - Page 1
Forum section: electronics / beginners

author: radlebb
author_rank: Newbie
timestamp: November 21, 2022, 10:40:11 am
content: Hi,Is an X2 Safety Capacitor like this:https://capacitorsfilm.com/product/safety-capacitor-x2-0-82uf275vac-polypropylene-film-capacitor/equivalent to one like this? Or is this not an X2?https://www.amazon.com/First-0-82UF-P20-Metallized-Capacitor/dp/B074TDS8TNi.e. the package seems quite different, the second being dipped, but will they essentially do the same job? I'm replacing a yellow one like the first link in a steam iron and am finding them hard to source without paying a bundle for shipping or it taking months to get here.Thanks

author: srb1954
author_rank: Super Contributor
timestamp: November 21, 2022, 11:36:01 am
content: Quote from: radlebb on November 21, 2022, 10:40:11 amThese are not at all equivalent. You should not use ordinary capacitors such as your Amazon example directly across a mains supply as they may fail and cause a fire in your equipment.The environment for an across-the-line capacitor is very arduous and it requires a specially designed and tested capacitor to safely withstand the conditions. You should only use safety-rated capacitors which are clearly marked with a rating class of X2 or X1 and have a voltage rating of at least 250VAC. You will note the other symbols printed on the case of the yellow capacitor: these are safety approvals which indicate that the capacitor has been tested against various international safety standards and approved by the relevant testing agencies.

author: dmills
author_rank: Super Contributor
timestamp: November 21, 2022, 06:03:09 pm
content: Also, Amazon marketplace for SAFETY CRITICAL PARTS??? Not sure that is a notably sane plan.

author: TimNJ
author_rank: Super Contributor
timestamp: November 21, 2022, 08:44:12 pm
content: Note that most film caps are marked with their DC voltage rating, so the red dipped cap is probably only rated for 250VDC anyway. (Remember 240VAC has 340V peaks.) If the cap is AC rated, e.g. an X-cap, you will usually see a “VAC” marking on it.It’s still a moot point because you shouldn’t use a non approved X1/X2 cap across mains in any case.

author: Terry Bites
author_rank: Super Contributor
timestamp: November 22, 2022, 10:07:43 am
content: Read dis:www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/As your X-caps go across the line and these caps may die slowly and/ or prematurely from mains spikes. Any old cap will not do. By design, class X will (hopefully) fail short so they take out the input fuse.This gives you protection during an overvoltage event. Without it the fuse would not blow and currents will continue to flow during the OV condition.Its not a perfect system, but it does help stop the explosion of the input caps in your smps.There should be no single fault condtion that can set in motion a cascade of failures. (swiss cheese analysis)Note that its common to put a MOV across the X cap to keep it (and your kit) protected from over voltage spikes. Its s good idea to put a MOV across both the Y-caps as well.Buy components from proper vendors not amazon eBay etc. Who knows where they're parts have come from. Traceability matters, especially when it all goes pear shaped.

author: radlebb
author_rank: Newbie
timestamp: November 22, 2022, 11:02:34 am
content: Thanks all. The markings on the dipped one we'ren't telling me much and I couldn't work out what a P20 was.Ideally would get this, but $15 for shipping is a bit ridiculous on a $2 item, so I was looking to find a cheaper option. I may have just do it though. The only walk in electronics shop in the City only stocks 100nF and 47nf.https://au.element14.com/wurth-elektronik/890324026024/cap-0-82-f-275vac-10-pp/dp/2456020Can I use a 0.47uF and a 0.33uF in parallel? Not quite 0.82uF...

author: wraper
author_rank: Unknown
timestamp: November 22, 2022, 11:14:11 am
content: Quote from: Terry Bites on November 22, 2022, 10:07:43 amBy design they fail open due to self healing effect (film metallization evaporating). The only X caps which commonly fail short (rather spectacularly) are Rifa paper garbage. Dunno who initially wrote that nonsense which is now spread all over internet about them intentionally failing short to trip a fuse. If you want that use a varistor. X capacitors are designed to fail safely without catching fire. While they sometimes can fail short, and self-healing effect is basically removing that failure by losing some capacitance, failing short is not an intended effect. Y capacitors are specially designed against failing short because it poses an electrocution risk.