Star,
no.
Y2 caps from Live or Neutral to Protective Earth (third wire) are not isolation.
If there is a fault the fuse isolates the mains from the user.
If the Y2 caps from Live to a floating ground (what is that?) exist inside a double insulated casing then I am not competent to comment on the legality of that design feature.
I cannot and won't say it is not properly designed. I cannot imply anything similar.
I said "Y2 do not isolate the mains side from the user side"
An isolating transformer does this.
Why do you think a Y2 cap is an isolating device?
no.
Y2 caps from Live or Neutral to Protective Earth (third wire) are not isolation.
If there is a fault the fuse isolates the mains from the user.
If the Y2 caps from Live to a floating ground (what is that?) exist inside a double insulated casing then I am not competent to comment on the legality of that design feature.
I cannot and won't say it is not properly designed. I cannot imply anything similar.
I said "Y2 do not isolate the mains side from the user side"
An isolating transformer does this.
Why do you think a Y2 cap is an isolating device?
I'm curious now. Do you have a part number? If it's cheap I'll go get one and take it apart.
what proportion blew a correctly rated mains fuse?
Or, were they all double insulated?
Over 90% of the switching wall warts have them. The main exceptions are the really small ones.
They are also common in internal power supplies. Here's a digital TV receiver with an internal power supply. The Y2 capacitors are blue and note that the receiver is not grounded.
http://www.nuxx.net/gallery/v/acquired_stuff/zenith_dtt900/IMG_0866.jpg.html
http://www.nuxx.net/gallery/v/acquired_stuff/zenith_dtt900/IMG_0881.jpg.html
C111 is neither to live nor neutral. It is connected between secondary ground and primary zero, i.e. the 0V reference for the rectified mains. It is connected to the " - " terminal of bulk electrolytic capacitor before the switching part (C103).
In this application, C111 allows high frequency coupling of secondary ground and primary zero, and helps to reduce CM noise and improve EMI.
These capacitors are rated to withstand high voltages (several kV 50/60Hz AC) for up to two seconds, making them safe for use accross galvanic isolation.
There is another one of these capacitors (C112) that runs from Primary 0 to case ground. It is the blue one just right of the mains connector.
In this application, C111 allows high frequency coupling of secondary ground and primary zero, and helps to reduce CM noise and improve EMI.
These capacitors are rated to withstand high voltages (several kV 50/60Hz AC) for up to two seconds, making them safe for use accross galvanic isolation.
There is another one of these capacitors (C112) that runs from Primary 0 to case ground. It is the blue one just right of the mains connector.
Just another note, to be absolutely clear:
These capacitors are NOT allowed between mains Live and Neutral and secondary ground. In this particular case they are allowed because they are in fact between two 0V references, subjecting them to much less stress.
switchmodepower is right. This device is grounded by the antenna inputs, making it essentially a class I device. therefore, the capacitor must be able to withstand 2120V. This (Vishay Datasheet) shows they are rated 2600V AC for 2 seconds.
voila.
These capacitors are NOT allowed between mains Live and Neutral and secondary ground. In this particular case they are allowed because they are in fact between two 0V references, subjecting them to much less stress.
switchmodepower is right. This device is grounded by the antenna inputs, making it essentially a class I device. therefore, the capacitor must be able to withstand 2120V. This (Vishay Datasheet) shows they are rated 2600V AC for 2 seconds.
voila.
Outdoor antennas must be grounded as required by code, but indoor antennas are rarely grounded. So it would not have any connection to ground if it is connected to an indoor antenna.
And the low side of the rectifier is quite far from ground whether the neutral and hot are connected correctly or not. Just measure voltage from that point to ground.
And the low side of the rectifier is quite far from ground whether the neutral and hot are connected correctly or not. Just measure voltage from that point to ground.
If you are referring to Cable TV networks, then these are normally grounded at least at the local distribution point. You are right however, that in terms of electrical safety, such ground could not be considered a safety ground... My previous post on that was rather firm on that, but after a good night's sleep I'm having second thoughts. Class Ior Class II, that remains the question....
Correct. But a DC offset w.r.t. ground or a remainder of mains AC after rectification does put a completely different kind of stress to these capacitors than when they are directly between Live, Neutral or Ground. IMHO, far less loading and hardly any stress in "pseudo-dc"...
Can you explain? All the XY capacitor application guides I can find only make distinctions between the "directly connected" (hot) part and the "isolated" part. They say that a Y rated capacitor must be used when bridging between those parts, but do not specify the points within those parts.
I remember about a VCR power supply that had a pair of Y2 capacitors from hot and neutral to isolated ground and another Y2 capacitor in series with a 330k resistor in order to derive the clock reference signal from the hot. No real ground, of course.
I remember about a VCR power supply that had a pair of Y2 capacitors from hot and neutral to isolated ground and another Y2 capacitor in series with a 330k resistor in order to derive the clock reference signal from the hot. No real ground, of course.
Hi all,
every class 2 power supply (ie. without ground connection) such as an wall
adapter or a mobile phone charger has an Y1 (not Y2) capacitor connecting
the primary side to the secondary side.
It is normally placed between the negative of the input bulk cap and the negative of the output cap. It is there only for EMI reasons : toghether with
the input common mode choke it helps reducing common mode noise.
UL allows to do this even if it is effectively a violation of the insulation barrier.
You absolutely need an Y1 (double insulation) or 2 Y2 caps connected in series.
The maximum value this capacitor can have is 2.2nF in order to reduce the touch current below 30uA.
Now in your application if your load does not need more than 30uA I think that is technically feasable without compromising the security but I have no idea if this can be approved.
Another point is that UL considers as live mains only what is in between the input and the rectifier bridge; after the bridge is no more treated as live mains (even if it is totally stupid). So to bridge the primary with the secondary you need to connect the Y1 cap after the rectifier bridge and not before.
every class 2 power supply (ie. without ground connection) such as an wall
adapter or a mobile phone charger has an Y1 (not Y2) capacitor connecting
the primary side to the secondary side.
It is normally placed between the negative of the input bulk cap and the negative of the output cap. It is there only for EMI reasons : toghether with
the input common mode choke it helps reducing common mode noise.
UL allows to do this even if it is effectively a violation of the insulation barrier.
You absolutely need an Y1 (double insulation) or 2 Y2 caps connected in series.
The maximum value this capacitor can have is 2.2nF in order to reduce the touch current below 30uA.
Now in your application if your load does not need more than 30uA I think that is technically feasable without compromising the security but I have no idea if this can be approved.
Another point is that UL considers as live mains only what is in between the input and the rectifier bridge; after the bridge is no more treated as live mains (even if it is totally stupid). So to bridge the primary with the secondary you need to connect the Y1 cap after the rectifier bridge and not before.
Mag is correct regarding bridging the isolation barrier with capacitors.
Safety regulations (EN/UL 60950-1) require that you use either two "y2" caps in series or one "y1" when connecting to mains supply greater than 150 vrms and bridging the isolation barrier between hazardous voltage and selv.
Safety regulations (EN/UL 60950-1) require that you use either two "y2" caps in series or one "y1" when connecting to mains supply greater than 150 vrms and bridging the isolation barrier between hazardous voltage and selv.
Mag is correct regarding bridging the isolation barrier with capacitors.
Safety regulations (EN/UL 60950-1) require that you use either two "y2" caps in series or one "y1" when connecting to mains supply greater than 150 vrms and bridging the isolation barrier between hazardous voltage and selv.
Safety regulations (EN/UL 60950-1) require that you use either two "y2" caps in series or one "y1" when connecting to mains supply greater than 150 vrms and bridging the isolation barrier between hazardous voltage and selv.
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