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I couldn't find this information anywhere.

Every tutorial on how to safely handle a capacitor tells you to absolutely avoid touching the capacitors leads, and to grab a capacitor by its insulated sides until you can confirm that the capacitor is properly discharged.

However, nobody ever mentions if the bare metal top of electrolytics capacitors is safe to touch or not. I'm referring to the pressure vents, indicated by the red arrow in the image:

enter image description here

I read a bit about the internal structure of a capacitor, and if I'm not mistaken the vents should be connected with its cathode (as all the capacitor case should be).

My interpretation is that touching the top metal ALONE should be safe, as you are only touching the negative "lead" of the capacitor.

However, touching the top AND the positive lead at the same time will get you shocked.

Is this assumption correct?

Please let me know what's the real situation if my reasoning is incorrect.

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The case is not necessarily connected to any terminal directly. Nichicon appnotes say that the case is has unstable resistance to cathode terminal and there is only layer of aluminium oxide and electrolyte, so it really is unstable.

So you should not assume that it is connected to any potential or that it is safe to touch.

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  • \$\begingroup\$ Thanks for the answer. So what you are saying is that "it depends", and nothing should be assumed, so it is best to stick to touching only the insulated sides of the capacitors? \$\endgroup\$
    – mars
    Dec 3, 2020 at 10:37
  • \$\begingroup\$ The same application note also says that the outer sleeve is not guaranteed to be an insulator. I don't understand why are you wanting to touch capacitors anyway. You should not touch live circuits. And if they are not high voltage or live circuits, it makes no difference if you touch the capacitors or let's say the 12V battery terminals directly, it's just as safe. \$\endgroup\$
    – Justme
    Dec 3, 2020 at 10:42
  • \$\begingroup\$ I'm sorry if it sounds as a dumb question. I don't want to touch a live circuit, but I read anywhere that even when disconnected from AC, capacitors can still be hazardous. How can I touch a capacitor on a PCB (for example for desoldering) disconnected from AC, if I cannot touch it anywhere? I know it should be discharged before touching it, but I'm still trying to understand what is the safer way to handle it. :) \$\endgroup\$
    – mars
    Dec 3, 2020 at 10:57
  • \$\begingroup\$ Discharge it first by temporarily placing a resistor across it (say 10K). Use a safe way to do this like using 2 proper multimeter probes to touch the capacitor termimals to which you've connected the resistor. Then, always measure before touching. \$\endgroup\$ Dec 3, 2020 at 11:09
  • \$\begingroup\$ @Unimportant OK, thank you. \$\endgroup\$
    – mars
    Dec 3, 2020 at 11:22

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