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I recently purchased a Corsair TX PSU and when it's on the Y caps are "sending" about 14v to the ground I'm not sure why this is happening but I already removed Y caps from my surge suppressor to fix this. Sometimes I know it's not possible to remove Y caps (connected between line-ground) but I wonder if this is safe when it comes to computer PSU

P.S: 103 Y caps and above are usually the worst when it comes sending voltage to my earthing system. I notice that between neutral and earth with everything off it's 0volts but when I turn on the PSU it goes above 12V

noiztmaker
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    What problem are you trying to solve by removing the Y capacitors? – Andy aka Jan 03 '21 at 11:36
  • Stop leaking voltage to earth (grounding) – noiztmaker Jan 03 '21 at 11:39
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    It's leaking current, not voltage, and very little at that. Why is it a problem? They *do* serve a purpose. – Unimportant Jan 03 '21 at 11:50
  • I usually do not understand why are Y caps on power supplies... honestly it's not a device that needs extra filtering. For what I understand the only reason Y caps are there (4 in total) is to filter EMI, right? – noiztmaker Jan 03 '21 at 11:51
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    XY problem! Current leakage to ground is not a problem by itself. – winny Jan 03 '21 at 11:53
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    If you have 12 volts between neutral and earth then the problem is that you have bad AC wiring. – Andy aka Jan 03 '21 at 11:53
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    Have a look at SE question "What does the Y capacitor in a SMPS do?" https://electronics.stackexchange.com/questions/216959/what-does-the-y-capacitor-in-a-smps-do – D Duck Jan 03 '21 at 11:57
  • is it safe to remove y caps on PSU though? – noiztmaker Jan 03 '21 at 12:04
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    It's not safe to have such a bad earth system. In fact it's downright dangerous. – Andy aka Jan 03 '21 at 12:06
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    *I usually do not understand why are Y caps on power supplies.* Then search this site and you **will** find the answer. The Y caps are there so provide a short path for the high frequency harmonics generated by the switching of the high voltage. Removing the caps will make those signals find their way through the air (it is radiated) and other unwanted paths. You might want to explain more precisely why the Y caps are a problem **for you** but are not a problem for almost everyone else! – Bimpelrekkie Jan 03 '21 at 12:15
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    I'd also say that in general it is not a good idea to make changes to **any** device that is mains connected unless you **fully** understand how that device works. I mean, be able to explain the design and what every component does. The Y caps are there for a reason, if it was OK not to place them **for sure** many PSUs would not have them so the manufacturer can save a few cents. – Bimpelrekkie Jan 03 '21 at 12:17
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    DO NOT JUST REMOVE THAT WHICH YOU DO NOT UNDERSTAND!. Y-Caps are there for a reason –  Jan 03 '21 at 12:26
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    You should not modify consumer equipment as it will first of all void the warranty and modifying equipment without understanding what you are doing can make them dangerous. – Justme Jan 03 '21 at 12:57
  • what's the function of Y cap on a notebook charger? There is usually only one Y cap. Aren't Y caps supposed to be a pair to filter? what's Y cap doing in notebook chargers? Same question for PSUs, I supposed there are only filtering Neutral-Earth and Line-Earth right? – noiztmaker Jan 03 '21 at 13:53
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    You need to fix whatever is wrong with your grounding, because that is the problem. A few milliamps of leakage current should not cause the ground voltage to rise by 14V. The Y capacitors are there to stop the power supply transmitting large amounts of electromagnetic interference to everything nearby. – Simon B Jan 03 '21 at 14:45
  • Y Caps are supposed to stop EMI from Line-Ground and Neutral-Ground if most of the noise comes from Line-Neutral that are already filtered by X caps, is there any risk in removing Y caps? – noiztmaker Jan 03 '21 at 23:19
  • I found a "STE Y2 CE 250VAC Ceramic Disc Capacitors 4700PF 500V" inside my Notebook charger. There is only one of this. For what I can see this is a decent Y safety cap but the only function of this cap is to filter Neutral to Ground since there is only one of this and not 1 pair. If I have Y caps in my surge suppressor to filter EMI what risk would be involved in removing Y caps from notebook charger and PSU? – noiztmaker Jan 04 '21 at 02:20
  • one risk is EMI emitted from the cable that supplies the notebook charger – Jasen Слава Україні Jan 04 '21 at 05:30
  • @Jasen other than EMI interference, a ceramic 4700pF capacitor is only there to filter EMI right? there is no risk this could be there for other application? I removed from two notebook chargers this capacitor and everything works fine, but I'm worried about shock risk or something else. Everything I've read point out this is working as a noise filter from neutral-to-ground basically. Strange but only computer power supplies have X caps (line-neutral) – noiztmaker Jan 04 '21 at 06:19
  • EMI can cause undesirable behaviour, but should not cause danger, if you remove the capacitor, it could mess up your, wifi, alarm, car remote, cell phone, etc, but you'll probably be fine until that dodgy earth kills you. – Jasen Слава Україні Jan 04 '21 at 06:27
  • I heard it's not uncommon for Y caps add "leak" voltage (~10 to ~40V) to the ground in old earthing systems (especially T-T [terre-terre[). I'll see if I can improve my TT system or perhaps switch to TN-S by hiring an electrical engineer – noiztmaker Jan 04 '21 at 08:45
  • @Andyaka See my answer and other comments. The voltage mentioned is due to the Y caps acting as a voltage divider across P-N and there being no earth connection. Worst case this can destroy products - often either a port or product connected to a port. I have seen printer destroyed in this way. Laptops will often cause minor shocks if touched if their psu has no ground connection and incoming 'ground' is connected dc or via a capacitor to the DC output ground. – Russell McMahon Jan 04 '21 at 11:45

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The Y caps form a voltage divider between phase and neutral with the unloaded voltage at their center point being at Vmains/2. Measurement with a voltmeter will usually show a lower voltage due to meter loading. (Try measuring Phase to midpoint and Neutral to midpoint. The result will not sum to Vmains/2).

The correct solution is to ground the Y resistor center point. As this is almost always connected to power supply ground this is usually achieved by using a 3 wire power cord with ground wire AND a power outlet with ground.

The problems usually occur when this ground connection is missing.
This is a safety hazard in its own right. Ungrounded outlets are more common in some countries than in others - but are less desirable than a grounded outlet for safety reasons.

The major task of the Y capacitors is to help remove 'noise' from the mains input - mainly from the power supply itself but they also filter incoming mains borne noise.

Removing the Y caps makes the power supply non-compliant to regulatory requirements and make it more liable to cause EM (electromagnetic) interference.

It may also make the device somewhat less resistant to mains borne EM interference. An X cap serves much the same purpose. The Y caps are balanced to ground IF ground is provided, providing a notionally superior result.

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Consequences:

The voltage mentioned is due to the Y caps acting as a voltage divider across P-N and there being no earth connection.

  • Worst case this can destroy products - often either a port or a peripheral connected to a port. I have seen a printer destroyed in this way.

  • Laptops will often give users minor but annoying shocks if touched if their psu has no ground connection and incoming 'ground' is DC connected or via a capacitor to the DC output ground.

Russell McMahon
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  • thank you for your answer. I do have an earthing and 3 pin socket, the issue is it's an old TT system (from late 70s). There is no shock or anything on my notebook from the charger with removed Y cap. I measured a metal piece in my notebook and the voltage is 12V. Obviously this metal is supposed to be protected by a plastic shell, I simply removed to make sure it's not leaking anything above 24V If I had no ground at all the voltage would be about 50% of 230VAC. In my friends house his earth and neutral measured as 106V his house is neutral-phase no grounding system – noiztmaker Jan 04 '21 at 12:22