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Comment by josefdlange | Hacker News Reader

Ungrounded adapter + bad mains power = zap!

Ungrounded adapter + clean mains power = probably no zap

Grounded adapter + bad mains power = probably no zap

Grounded adapter + clean mains power = no zap

It's not just the adapter and it's not just the mains power; it's when both come together. Electricity follows pretty simple rules when it comes down to it.

Always always always ground your A/C connections. Why wouldn't you?

Also, never use one of these unless you've attached the little wire/alligator terminal to a ground somewhere:

http://www.prestonelectronics.com/audio2/ttip/images/gndadap...

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I knew a guy in college who rented a house that didn't have any outlets with a ground plug.

This became such a problem, he made his own ground by using a big metal pipe outside the house that was already deep in the earth, and running a wire from it to where he kept all his equipment.

Then he used stuff like in that picture to make sure he could ground all his equipment.

This is the right way to use those! It's so rare to hear of proper usage.

You can also screw them to the outlet box, which should already be grounded, especially if it uses older BX sheathing.

Actually, for things with a non-conductive casing (think cheap nightlights, or those apple wall warts) there's no need for a ground. If anything, it's another part and more cost, thus it isn't included.

In highly sensitive A/V systems, an isolation transformer is often used as well, neglecting a ground.

These are all better and more knowledgeable points than my own! I definitely only speak out of an abundance of caution having known people whose bad electricity and habits have damaged property.

You have to be careful with isolation transformers because there is one gotcha... the ground pin normally passes through to earth. I've witnessed someone blow up a nice $5000 Agilent oscilloscope before I could stop them because they didn't understand how to use an IT and plugged the scope into it so they could probe AC. Bad news, you're supposed to plug your test device into the IT not the scope because the BNC connectors in almost all oscilloscopes are connected straight through to the earth pin.

I heard "POW" from across the lab as soon as he clipped the probe on and knew I should have warned him. Nobody was hurt apart from our lab budget.

Humorous demonstration of the same mistake: https://youtu.be/sI5Ftm1-jik?t=2m20s

I can't tell, the second boom where he holds the resistor in place was that on purpose? If so holy shit that's a dangerous way to make the point. If it was also an accident then he is lucky to be alive since he doesn't seem to know what he is doing.

I know this video is supposed to be funny, but I couldn't bring myself to laugh. Too many people die making the same mistakes.

He does know what he's doing and it certainly was deliberate. While most of his stunts probably hurt he doesn't set them up exactly as he presents them (I.e. it's usually not mains).

I got the zaps. I live in the Uk where we have good quality mains power, and my mains power and all the sockets are tested once a year.

"clean" mains power has nothing to do with zapping. Where'd you hear this? I've literally never heard this nonsense before.

I suppose a neutral line with a nonzero voltage could be called "dirty", but not in the traditional noise sense.

That still doesn't cause zaps unless you were living in the Edison days or something.

That's exactly what caused minor zaps on older equipment that has a metal case connected to the neutral line.

How old are we talking about? That sort of shit hasn't been happening for ages.

I definitely used the wrong word -- I intended this meaning.

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