What is the "better / best " method to multi-boot different OSes natively WITHOUT VirtualBox(es) ?

Valeri Galtsev galtsev at kicp.uchicago.edu
Mon Oct 26 04:12:01 UTC 2020

> On Oct 25, 2020, at 4:52 PM, Ralf Mardorf <ralf-mardorf at riseup.net> wrote:
> On Sun, 25 Oct 2020 11:39:48 -0700, David Christensen wrote:
>> On 2020-10-25 05:54, Ralf Mardorf wrote:
>> Please explain how galvanic isolation relates to electrostatic
>> discharge mitigation.
> That's a misunderstanding.
>> Please explain the risk(s) associate with antistatic wrist straps.
> IMO it's a risk for a human being to wear an antistatic wrist strap,
> when getting in touch with gear that is connected to the mains.
> IMO if the gear isn't directly connected to the mains, because an
> isolating transformer grants galvanic isolation, an antistatic wrist
> strap isn't a risk for a human being.

Well, anti-static strap is used when one is working on fully disconnected from power equipment on the bench which is metal or slightly conducting mat which is connected to the “ground” which is specially arranged thing I will not go into discussion about. In this setup there is no danger to person using this strap. Several people disregard using strap, and single conducting mat. However, they have set of habits (often from their ham times - radio amateur that is). These habits will be: putting static sensitive boards on anti-static bags, and touching bag before picking up the board, then touching metal chassis before installing board… works the same way as strap.

> An antistatic wrist strap protects the gear against static charge, but
> might be risky for a human regarding potential equalization, assuming
> something should be fishy, such as a hot metal case. Once the human
> touches the hot metal case a fault current breaker should detect that
> something is missing, but galvanic isolation is way more secure than a
> breaker that probably is missing that something is missing.

If anything is plugged to AC, there always is stray capacitance, and through that capacitance the voltage of hot lead can be on some pieces inside device. Of course, stray capacitance is small, acts as big value resistor, however “discharging” even that small resistor through some high impedance pin of (static sensitive) board can be fatal for some IC (integrated circuit) on the board. Can be safe but not always is for a human accidentally touching that spot. Incidentally, I did myself several times stupid thing: touched 220V (AC) hot lead and got shock. Neither led to gross consequences, but it could… I was very young then.

So, we do our best to work inside equipment when it is fully disconnected from AC. Pull out all AC cords!

> Actually the fault current breaker should already do it's job, when the
> metal case is hot, already before a human does touch it. If it doesn't,
> then touching the metal case might be dangerous with or without
> wearing an antistatic wrist strap.
> However, galvanic isolation is absolutely safe, unless getting in
> contact with both conductors, which is impossible in our scenario and
> even very unlikely when repairing gear. 

Hm, if galvanic you mean DC isolation (i.e. AC transformer), then I disagree. In case of AC stray capacitance (which always exists) conducts some of AC line voltage to "DC isolated" part of equipment. Only optical isolation is full isolation, but we didn’t learn yet how to transfer sufficient power using purely optical connection. In general, DC isolation, like transformer, is safe, but transformer has stray capacitance, and what usually saves the day that low voltage part kind of shunts what comes through stray capacitance by not to small resistance. There may be less usual situation when highly isolated from everything piece of equipment has big capacitive coupling to “ground” which can be charged gradually through small stray capacitance of transformer (rectifier of one sort or another will be in play, call it “stray rectifier"). Even though it falls under what you call “galvanic isolation”, it represents big danger for a human, as big capacitor can sustain significant current for long enough time to do harm to living being.

My apologies, if I misunderstood you.


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