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I have a question regarding ESD.

My body can be electrically charged, for example if I have walked on carpets. In such a case if I touch the earth pin of one of my household outlets, an ESD will happen and the excess of charges within my body will transit to the earth.

If, instead of touching the earth of the outlet, I touch a pin of a PCB which is battery-powered and has no connection to earth, will an ESD happen? And if I touch any metallic object which has no connection to earth?

If so, why? Shouldn't there be a closed-circuit for current to flow between two objects?

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  • \$\begingroup\$ The closed circuit would be via the capacitance in air if you draw it. The reason why you ground yourself is because with white sole shoes and a fleece jacket, your movement is what chargers you up compared to ground. You may be able to charge the object up, but it’s far less likely. Can you touch the chassis of your battery power equipment before any of its ports? \$\endgroup\$
    – winny
    Feb 21, 2022 at 11:05
  • \$\begingroup\$ You might want to take a look at the answers to this question: electronics.stackexchange.com/questions/253160/… or this electronics.stackexchange.com/questions/410606/… or this electronics.stackexchange.com/questions/427277/… \$\endgroup\$
    – kruemi
    Feb 21, 2022 at 11:16
  • \$\begingroup\$ door knobs don't even contain batteries ... and they do not form a closed circuit \$\endgroup\$
    – jsotola
    Feb 21, 2022 at 19:49

2 Answers 2

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You can charge a capacitor from an electrostatic discharge when that capacitor has one terminal connected to earth. Do you see any problem here: -

enter image description here

An insulated item of electrical equipment will have capacitance to earth. OK, it may only be a few pico farads to several nano farads but, nevertheless it will "take" charge from your body when you touch it. Regard it is the upper plate of the capacitor in my picture.

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Short answer: Yes, it can happen (and will)

The reason is, that electric charges can equalize even if there is no connection to GND. Electrostatic charges are store in the electric field. It might make more sense if you think the other way around. Imagine the battery powered device is charged and you're connected to GND. If you touch the charged device it will discharge quickly (and is maybe destroyed).

The problem with ESD is not the high voltages but the fast discharges of the charges (and yes, the higher the voltage, the faster the discharge). The art of ESD-protection is in controled discharge that does not damage sensitive components. It's the case when designing an EPA (ESD protected area) in a lab or production facility as well as when designing devices that should be operated outside such an area. You basically have to create a miniature EPA in your device to protect it.

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