I'm watching LTT's new video with Electroboom where they shock RAM with an ESD gun. In some occasions, they do it without grounding the RAM stick. Doesn't the current have to go back to the source? I see 2 explanations (there could be another one).

1. Does the current actually flow through the things that the RAM is resting on, for example table, and not into the RAM?
2. I heard Linus say something about equilibrium, which seems to debunk the 1st question. If question 2 is false, then how does a 12kV potential develop between the ESD gun and the RAM stick? Or any potential in electrostatic phenomenon, like lightning or rubbing your feet on a carpet and touching a doorknob. Does it happen due to capacitance?

Water analogies welcome.

• The thing about static, is to forget circuits models and flowing in a loop. Circuit models are a simplification of a small group of well-defined physics we use a lot to make things easier to work with. But static electricity is outside of these definitions and operates on more general physics. Does air have to flow in a closed-loop? Well, if you want it to flow continuously it does. But we also know that it doesn't need to flow in a loop. You can just connect a higher pressure gas tank to a lower pressure gas tank and the air flows momentarily. Static electricity is the same. Commented Dec 22, 2020 at 21:46
• Air has capacitance between conductors with leakage by dust and humidity so yes it can transfer through surface charges like a table. Charge can be generated by triboelectric effects Commented Dec 22, 2020 at 21:49
• @DKNguyen I think that's the makings of an answer, not just a comment. Commented Dec 23, 2020 at 3:56
• @Hearth Ugh I didn't want to go into more detail lol. Commented Dec 23, 2020 at 6:26

The thing about static, is to forget circuits models and flowing in a loop when starting out. Circuit models are a simplification of a small group of well-defined physics we use a lot to make things easier to work with.

But static electricity is outside of these definitions and operates on more general physics. You can use circuit models to model what is going on but it is just going to confuse you if you don't think about what is physically going on first because the circuit model in the case of static is more of a charge-accounting, book-keeping method rather than something that reflects what is actually going on and where/how charge is moving.

For example, we all know a floating steel ball can pick up a charge if you touch another charged object to it, and that acquired charge can be measured with respect to other things, but the steel ball has just one "terminal", the conductive surface of the ball, and when the charge entered the steel ball it entered one-way. Nothing flowed out to make a closed loop (unless you count leakage to the surroundings but that happens over a much longer period of time than it took for the charge to initially flow in.). There's a mismatch in time when you look at the closed loop charge flow.

But in the circuit model, the only thing that holds charge is a capacitor so that would model the steel ball. But the capacitor has two terminals whereas the metal ball only had one. One terminal is like the surface of the steel ball, and other terminal is connected to whatever you are measuring the acquired charge against, but the steel ball has no such connection, yet it still holds a charge which can be measured relative to other things. And when the capacitor charges up current does flow in and out at the very instant the charge is acquired. There's a mismatch between physical reality and the circuit model but it's useful for keeping track of and calculating things.

So forget circuit models, closed loops, and free space capacitance for now.

Does air have to flow in a closed-loop? Well, if you want it to flow continuously it does. But we also know that it doesn't need to flow in a loop. You can just connect a higher pressure gas tank to a lower pressure gas tank and the air flows momentarily. Static electricity is the same. Just think about metal balls carrying around charge and equalizing charge between the two whenever two balls touch.

And I'm feeling lazy so just read this which I wrote a while back: Are ESD safe tools necessary with proper setup?

• Is 12kV in static charge a lot of energy? Is there a formula that someone can use to calculate the voltage and charge and energy between to bodies of known mass and material? Commented Dec 23, 2020 at 10:48
• 12kV is middle ground as far as how strong ESD tests go. High end is 15kV and 30kV. Yes, you can calculate. You use the capacitor formulas Q=CV for a body and for C you use the free space capacitance of the body which is the capacitor made by the body's surface area and plates at infinite. Approximate body as a sphere with same surface area surrounded by another sphere at infinite. Commented Dec 23, 2020 at 14:19
• That is from Henry Ott's book Electromagnetic Compatibility, Section 15.1.2 and boils down to $C=\frac{\epsilon A}{D}=\lim_{r_1 \to \infty}\frac{4\pi\epsilon}{\frac{1}{r_2^2}-\frac{1}{r_1^2}}=111r$ when using spheres as outlined above. Commented Dec 23, 2020 at 14:34
• That is where the human body model gets 30pF and that is how you calculate the voltage after and before the discharge when touching an object (Q is equal between the two objects after touching and the voltage each charges up to depends on their surface area/free capacitance). Really tiny charged body discharging into really big neutral body = both bodies approach 0V. Really Big charged body discharging into really tiny neutral body = both bodies approach initial voltage of big body. Not unlike pressure between big and tiny tanks after being connected together. Or capacitors. Commented Dec 23, 2020 at 14:38
• Result C is in pF, by the way. Commented Dec 23, 2020 at 14:57