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Old 26th Feb 2021, 6:46 pm   #1
Gabe001
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Default Capacitors with combined X/Y ratings

Looking for some advice, just a quick one I hope.

I bought a Philips live chassis radio as a donor set but I've gone soft and decided to restore it. Swmbo likes it, go figure.

I'm trying to look for some type y capacitors for the pick-up, aerial and earth sockets, but all I can find are ones with combined X/Y ratings.

If the cap is rated x1/y2 for example, is it suitable for this location? I understand that it can meet the safety voltage criteria mandated by the X/y rating, but will it fail short (and electrocute me) or open?

Thanks
Gabriel
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Old 26th Feb 2021, 7:09 pm   #2
GMB
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Default Re: Capacitors with combined X/Y ratings

I never heard of rating both X and Y. Who is doing that?

If it claims Y class then it must be safe for earth connection. Y class capacitors are like two caps in series so if one fails short it is still a capacitor.
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Old 26th Feb 2021, 7:18 pm   #3
cathoderay57
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Default Re: Capacitors with combined X/Y ratings

Does this link help? https://www.justradios.com/X1Y2capacitors.html Cheers, Jerry
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Old 26th Feb 2021, 7:24 pm   #4
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Default Re: Capacitors with combined X/Y ratings

I'm surprised it's possible to conform to both the X and Y specs at the same time, but apparently it is.
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Old 26th Feb 2021, 7:59 pm   #5
GMB
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Default Re: Capacitors with combined X/Y ratings

The clue is that it is X1 but Y2.
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Old 26th Feb 2021, 8:07 pm   #6
Gabe001
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Default Re: Capacitors with combined X/Y ratings

Vishay, Murata etc seem to do x1/y2 ceramics. It appears to be quite the norm.

I understand the rationale for the X and the Y types, but am I to believe that it fails open or short depending on where you place it in the circuit? Is that even possible?

Gabriel
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Old 26th Feb 2021, 8:11 pm   #7
Gabe001
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Default Re: Capacitors with combined X/Y ratings

Quote:
Originally Posted by GMB View Post
The clue is that it is X1 but Y2.
That's what I thought initially, but you can have X1/Y1 types too e.g

https://www.ebay.co.uk/itm/4pcs-2200....m46890.l49292
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Old 26th Feb 2021, 11:30 pm   #8
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Default Re: Capacitors with combined X/Y ratings

https://www.allaboutcircuits.com/tec...-y-capacitors/


Seems to explain it fairly well.


In a nutshell, you may use Y only rated capacitors in an X application if you wish- they're just overspecified for the job. You may not use X only rated capacitors in a Y application since they are permitted to fail short circuit.
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Old 26th Feb 2021, 11:35 pm   #9
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Default Re: Capacitors with combined X/Y ratings

I think the idea of X failing short and Y failing open is a myth or gross simplification.

In general they both use the same dielectric and plates. They are usually meant to be "self healing" after a breakdown. The Y class is constructed so it needs 2 dielectrics to short out to be dangerous.
Otherwise it is down to voltage ratings with Y having to be much better than X. Also Y has a limit on value to avoid excessive current flowing to earth.
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Old 27th Feb 2021, 7:13 am   #10
Gabe001
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Default Re: Capacitors with combined X/Y ratings

Thank you for the explanation. That makes a lot of sense.
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Old 27th Feb 2021, 7:17 pm   #11
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Default Re: Capacitors with combined X/Y ratings

The small available values of Y caps (1nF or so) was originally set so that the resulting capacitive current to earth would not operate an earth leakage trip.
Some early Japanese microwave ovens did cause problems because they had high values for Y caps to meet EMC requirements.
The manufacturer's excuse was that it was designed as a fixed appliance and should ideally be permanently connected (then why supplied with a plug?) and as such did not need to be leakage protected

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