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 Post subject: Safety capacitors?
PostPosted: Jun Sun 16, 2019 10:26 am 
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Sorry, feeling dumb right now.
I've seen them mentioned here, and even on a vendor's site where it specifically says that they won't make your radio safe.
So what are they for?
Thanks,
Russ


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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 16, 2019 10:34 am 
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They are specifically designed to make you feel you have done something important, when you haven't.

Some equipment needs to have an AC connection to chassis ground, like some generators. They used disc capacitors in the past, and rarely had problems. Now they have "better" capacitors, call 'SAFETY' capacitors that (shock) cost more.


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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 16, 2019 12:09 pm 
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The term "safety capacitor" seems to mean that they make something safer. They actually do, but only if they should fail. They do NOT make your radio any safer in normal use, but if one of them should fail, they are designed to fail in such a way that they do not connect one side of the AC power line to the chassis, or in some cases, the term "safety" has been used for a capacitor that cannot cause a fire if it fails. Hence the term "safety". It tends to get a bit confusing, depending on which write up online you prefer to read. I'd suggest you google the term 'safety capacitor' and read several different articles from various places. I've pasted two in below as a starting point.

Here's a write-up from Kemet: http://www.kemet.com/Lists/Filestore/EvoxRifaRFIandSMD.pdf ..........complete with pictures!!! :-D

quoted from stackexchange.com, and edited and shortened by yours truly:. NOTE: I do not necessarily agree with this particular article; it is but one of many, and some have a completely different take on it. For example, it's been stated that the X capacitors are designed to fail open, rather than shorted. I cannot find anywhere that actually states this.

"Safety capacitors are classified by X and Y ratings. Let's properly define everything, and then it should become clear how those capacitors can be rated for both X and Y at the same time.

Class X Capacitors: These are capacitors are only for use in situations where their failure would not present an electric shock risk, but could result in a fire. That is all. There is no specification as to its failure mode, if it fails open or closed, or if it is across-the-line or not.

However, this ultimately amounts to these capacitors being used in across-the-line situations, as line-to-ground situations carry the potential for electric shock risk if those capacitors fail shorted.

Now, no one wants a capacitor to fail shorted, as this is rarely a sure-fire way to blow a fuse before the capacitor explodes or catches fire. When they fail closed, they often still present several ohms of resistance, rather than being a dead-short. So, X capacitors aren't really designed to fail open or closed circuit per se, but are designed to withstand a great deal of surge without failing at all.

from me (For both X and Y capacitors, the 1, 2, or 3 in the type number is the voltage rating .... look them up as needed.)

"Class Y Capacitors: These capacitors are rated for use in situations where failure would present an electric shock risk. What this means is, Y class capacitors are designed to simply not fail at all, or be self-healing, allowing them to recover from an arc-over event. Basically, the requirements for a class Y capacitor are stricter and higher than that of an X Capacitor. And Y capacitors are the only capacitors rated to be safely used in 'line-to-ground' situations. However, again, there is not any mention about their failure mode, the Y rating only implies certain minimum requirements are met. This amounts to not failing at all generally, or, as mentioned, being self-healing.

Only Y class capacitors are sufficient for use in 'line-to-ground' applications. Because of the stricter safety ratings, it is acceptable to use Y-rated capacitors in place of X-rated capacitors, but not vise versa. Capacitors explicitly rated for both are not uncommon, and there is nothing preventing a capacitor from being both classes at once.

Both these tables are generalizations, and depending on which standard was used when designating a capacitor as an X or Y class, the specifics may vary slightly. If you really want to get into the nitty gritty details, it's best to read the specific standard for a given capacitor.

Finally, while not mentioned in your question, I would like to add the actual purpose of these capacitors. They are used for EMI filtering. They not only block a good deal of garbage from mains getting into your device, but likewise prevent your device from dumping garbage into the mains. In general, these will be present on switch mode power supplies out of necessity to pass FCC/CE/whatever, but will usually be absent on old-school linear supplies (a mains transformer alone is performing the voltage step-up or step-down). This is due to the significant switching harmonics that is an inevitable side-effect of fast rise and fall times seen in switchers, while a linear transformer is comparatively low-noise/low-harmonic. The bridge rectifier causes some harmonics, but the iron-laminate core dissipates virtually all of those well before they can make it back into the primary winding"

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Last edited by Barry H Bennett on Jun Sun 16, 2019 1:56 pm, edited 2 times in total.

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 16, 2019 1:46 pm 
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Prior to the term "safety capacitor," they were known as "UL capacitors," at least in this country. The designation meant that the capacitor was tested and recognized by UL for connection with one side, or across the AC line. In order to get that designation, UL had to test samples of those capacitors and ensure that their design and manufacturing standards were upheld. If a capacitor with this classification failed for any conceivable reason, it could not start a fire or create a shock hazard. Most ordinary capacitors are not tested nor rated for this.

Now it has to be understood that most of the electronic components that the world produces go into bigger, more complicated products made by other manufacturers. Those other products, whether they be TV sets, radios, cellphone chargers, computers, LED light bulbs, microwave ovens, etc., are also usually inspected and certified by safety agencies. Most larger retailers won't touch electrical products that are not approved by at least one of the major labs in the world. So when those inspectors open up the products and see those special markings on the capacitors connected to the AC line, they know the correct kinds of capacitors were used. That's really the whole point.

Since most electronic components are not made in the US any more, the term "UL capacitor" became obsolete and was replaced by "safety capacitor." One could wish they picked a different name as it's the capacitor that is "safe," not necessarily what you put it in. But most people feel that when dealing with vintage electronics it is preferable to use capacitors having those designations on the AC line circuits, since most other kinds of capacitors are not rated for that kind of service and it is improper to use them that way.

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 16, 2019 2:25 pm 
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Years ago, manufacturers used 400 WV capacitors as line filters. Nearly everyone I came across was bad and a possible shock hazard. Awhile back, I got a box of .01 uF 3 KV disc caps that I use for this purpose.

Dennis


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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 16, 2019 2:41 pm 
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There is also a good writeup here:
https://www.justradios.com/safetytips.html

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 16, 2019 3:21 pm 
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One other factor not mentioned: part of the approval by safety agencies is a test using transient high voltage pulses and high voltage AC. Different classes will withstand 2KV, 4KV, and higher. Transient voltage spikes are common on AC power lines. DC rated capacitors won't have these tests.

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Mon 17, 2019 1:31 am 
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Glad to see Just Radios updated their "safety capacitor" comments. The former explanation was misleading and suggested that "safety capacitors" somehow added to the safety of a radio under normal conditions.

Rich


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 Post subject: Re: Safety capacitors?
PostPosted: Jun Mon 17, 2019 5:25 am 
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I know some may disagree, but I never use safety capacitors. I also never polarize my line cords. When the chassis is in the cabinet, knobs on and back installed (like the radio was intended to be used) they are perfectly safe as-is (with leaky paper capacitors replaced, of course).

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Mon 17, 2019 7:32 am 
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Thanks, all.

I agree, wish they had chosen a different name, but now I have a clue at least.

I have seen these mentioned several places, and didn't know what their purpose was. Appreciate all the info.

Russ


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 Post subject: Re: Safety capacitors?
PostPosted: Jun Mon 17, 2019 4:31 pm 
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One other comment seems appropos: anybody can say any capacitor is a "safety cap." There is no police force going around and checking up on it. However, real capacitors of this type are well marked with the name or logo of the manufacturer, their part or catalog number, the safety agencies that approved them and their file or reference numbers, date code, and of course the electrical specs. If you come across capacitors without these markings, or did not get them from a manufacturer's authorized dealer, they may not be any safer than ordinary capacitors--because that may be exactly what they are.

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Mon 17, 2019 5:04 pm 
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One thing is for certain, though---just about any type of new cap is going to be a safer upgrade to leaky paper ones

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Mon 17, 2019 5:26 pm 
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Depends. If you are talking about a capacitor that is connected across the line (a line bypass cap), then yes, just about any new capacitor will be safer than a degraded paper one. A shorted paper capacitor can get hot enough to start burning if there's enough energy available; metalized plastic film tends to burn away where pinhole shorts occur and "heal."

The thing is, the plastic film in ordinary capacitors is not designed to withstand the spikes and surges in commercial AC power, so it will likely do a lot of "healing" and may develop more serious shorts, in which case it could burn up too. X2 or XY2 'safety' capacitors are made of materials certified to be flameproof, have dielectrics tested to withstand line voltage spikes and surges indefinitely, and are designed to fail open.

If you are talking about line-to-chassis situations, a short in an ordinary film cap may not burn itself out and you end up with a hot chassis. This is exactly the situation Y2 or XY2 'safety' capacitors are designed to prevent.

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Fri 28, 2019 2:56 am 
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tubes4life wrote:
I know some may disagree, but I never use safety capacitors. I also never polarize my line cords. When the chassis is in the cabinet, knobs on and back installed (like the radio was intended to be used) they are perfectly safe as-is (with leaky paper capacitors replaced, of course).

I do not disagree one bit.

steve

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Fri 28, 2019 12:13 pm 
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I hate to quibble, but:
tubes4life correctly points out that safety can typically be had by using the radio as it was intended....eg keeping it in its case with its knobs on

.....and maybe also not using it in the shower....;)

BUT: "Safety caps" add a different kind of safety---that was not widely available when many AA5/6 radios were made. As is already thoroughly belabored, they do not add safety in normal operation. But they do offer an additional layer of protection in that the part can fail without creating an additional hazard.
Of course, if you don't have any line filters or such, then "safety caps" are not relevant.

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sat 29, 2019 5:32 am 
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i have never used a safety capacitor and probably never will unless someone gives me some.

i don't plan on "adding an ipod jack", a polarized plug, putting the hot side on the switch, completely rewiring a set to float the B- and do any other thing to the radio.

those topics are beat to death on here every few weeks.

i too completely agree that if the common hot chassis set IS used properly with all pieces in place, nobody needs to update their will.

i don't think grandma ever touched the bottom chassis bolt, stretched herself to the sink, and got herself a glass of water at the same time to see what will happen.

steve

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 30, 2019 12:43 pm 
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Dutch Rabbit wrote:
tubes4life wrote:
I know some may disagree, but I never use safety capacitors. I also never polarize my line cords. When the chassis is in the cabinet, knobs on and back installed (like the radio was intended to be used) they are perfectly safe as-is (with leaky paper capacitors replaced, of course).

I do not disagree one bit.

steve


You forget that not every radio has a back. You also forget that LITTLE CHILDREN can get tiny fingers to the hot chassis through the back and get zapped! Some radios, a Hallicrafters comes to mind, have metal on the front of the radio that is grounded to the chassis for hum purposes, or just contacts the chassis when all put together. You can get a nasty shock that way. Many older radios had STEEL cases around them. Almost all Hallicrafters SW radios do and a bunch of them were AC/DC. Even sets with transformers will do that. So, those rules don't apply in every case.


FWIW, the terminology use to describe certain parts comes to us from overseas, i.e Europe or Asia. As far as the safety concern goes, the size of the line bypass cap has a LOT to do with bypass current to the chassis. In years past the capacitors were MUCH larger that necessary and posed much more of a shock hazard. UL's terminology has already been discussed, but thinking about fire/shock hazard is always a good thing. Remember too, that most of the old radios you deal with were designed to work in a setting where there was no good path to ground, except in a kitchen or place where a water line was present. That is not the case now. So, some consideration needs to be given to the environment that the radio is going to live in NOW. Personally, I make sure that the chassis, and case is at 0 volts when the set is on or off and the line bypass caps are small enough to do the intended job, without making enough AC current present to give someone a shock, or worse. Sometimes that means rewiring the heater string and bypassing in the set to accomplish that. Its also true that the bypass caps will bypass enough current to trip a GFCI breaker. So the size of the cap becomes a consideration. Just some things to think about.

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 30, 2019 1:52 pm 
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Look, nobody says you have to have an antique radio. If they are that bad, maybe you should cut the cords off and just keep them as decorator items, or just smash them up and throw them away so nobody gets hurt. Why stop with shock hazards? Ever burn your fingers on a red-hot ballast tube? Drop a heavy boatanchor chassis on your foot? Cut your fingers on a broken piece of dial glass which was not tempered or laminated? Got asbestos dust on yourself from old line cord insulation or cabinet lining? New radios are available which work just as well if not better, but do not come with any of the hazards inherent in old ones.

I use safety capacitors in across-line and line-to-chassis applications for one very simple reason. If you can find the spec sheets for them, you'll find that virtually none of the ordinary polyester plastic film capacitors that are commonly used for replacements in radio circuitry are designed, rated, or tested for operation on AC lines. In fact, some spec sheets warn you explicitly that the caps are not recommended for use in line applications or that the voltage has to be derated to 20% of the DC value. If they were satisfactory in line operation the manufacturers would be more than happy to claim it; AC capacitors are necessarily heavier and better built than ones designed to operate on predominantly DC circuits.

Using a component in a manner the manufacturer did not intend is never a good idea. X2 and Y2 capacitors are specifically made for AC line applications, so they are the right parts to use in those places.

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 Post subject: Re: Safety capacitors?
PostPosted: Jun Sun 30, 2019 2:22 pm 
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Chris108 wrote:

I use safety capacitors in across-line and line-to-chassis applications for one very simple reason. If you can find the spec sheets for them, you'll find that virtually none of the ordinary polyester plastic film capacitors that are commonly used for replacements in radio circuitry are designed, rated, or tested for operation on AC lines. In fact, some spec sheets warn you explicitly that the caps are not recommended for use in line applications or that the voltage has to be derated to 20% of the DC value. If they were satisfactory in line operation the manufacturers would be more than happy to claim it; AC capacitors are necessarily heavier and better built than ones designed to operate on predominantly DC circuits.

Using a component in a manner the manufacturer did not intend is never a good idea. X2 and Y2 capacitors are specifically made for AC line applications, so they are the right parts to use in those places.

+1

We now have various opportunities to put in parts that will be better and more reliable than what was installed 50-100 years ago. When radios were built with paper/wax capacitors, they were deemed "good enough", but now we have film caps that are better and maybe even cheaper (corrected for inflation). How many restorers advocate somehow finding or making P/W capacitors?

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 Post subject: Re: Safety capacitors?
PostPosted: Jul Tue 02, 2019 5:54 pm 
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I've seen AC/DC radios that used 200 VDC paper caps between the line and chassis. :roll: Not replacing them with parts that are UL APPROVED for that service is just plain wrong and dangerous. No matter how smug it makes you feel, it is bad advice to give to a newcomer on this forum. You can get away with less, but....

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