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Comment by elif | Hacker News Reader

It's terrible how little basic electronic safety is practiced in virtually all of these videos. When we handled high amps in university, we had 3 hours of lecture first simply explaining safety precautions and how to handle accidents.

Not to mention, the burnt wood looks so gaudy and uninteresting. I would hardly call it fractal as it only goes 2-3 levels usually, and artistically doesn't usually make sense on furniture etc.

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It probably should have been more than 3 hours given that you likely mean "voltage" not "amps".

Before everyone jumps on me, "it is the amps that kill you, not voltage", I understand electricity quite well and in this context, saying something like "handling high amps in a university" is almost certainly not what was taught.

Also, it's not electronic safety, its straight up electrical safety. There are no electronics in a magnetron.

Even with power electronics we still say electrical safety

It was a class on embedded electronics and robotics. There are more hazards in electronics than merely electrical hazards. e.g. exploding capacitors, toxic fumes, etc.

A magnetron is a vacuum tube which works by swirling space charge around. Vacuum tubes are "electronics"; the word "electronics" was originally invented to distinguish vacuum tubes (where it matters that the charges are being carried by electrons) from previous electrical devices such as relays, resistors, condensers, motors, generators, and inductors, where you can pretty much ignore the nature of the charge carriers.

Surely the magnetron itself is an electronic device.

Rather than admonishing everyone for wondering the obvious question, why not just explain your reasoning?

High amperages are really only dangerous (in terms of electrocution) with higher voltages. As voltages get low enough, our bodies' resistance means that there won't be enough current passing through you to hurt you. The dryness of the contact point makes a big difference (several orders of magnitude), but even with wet hands, it is pretty much impossible to hurt yourself with < 12 volts.

The risks with low voltages and high amperages are from shorts causing rapid heating.

Current flowing through your body is what kills you. But it doesn't flow through you just because it is a high-current supply (think car battery for example). It flows through you because the source voltage divided by your impedance is what controls how much current flows through you. Impedance is the general concept for resistance and basically indicates how current and voltage are related. The higher the impedance, the less current flows. Wearing rubber gloves would increase your impedance from hand to hand significantly.

So while high current does kill you, what causes it is high voltage. What is considered high? Depends on your impedance (ex. are your hands sweaty or dry?).

When dealing with high-current systems, there are safety procedures and concerns, but they are generally different than high-voltage. The systems I have dealt with are more about burns than electrocution. For example accidentally shorting out a fork lift battery can be spectacular in a bad way.

There's no particular safety concerned when you're playing with hundreds of kilovolts in a typical school. You need it when the thing you're messing with has the capability of delivering a lot of amps.

415 volts on a 30A breaker, like you might find in an undergraduate electrical engineering lab, is very lethal. I'd hazard a guess that's what the OP is talking about.

415 volts on a 5A breaker is equally lethal, and not high-current.

1,000 Amps and 5 volts is dangerous (sort of), but not in an electrocution sense.

What you care about is how much charge is at that high voltage potential because current is charge/sec. Charge due to stray capacitance can be quite dangerous because if you don't know what you are doing, the amount of stray capacitance can be higher than you expect. I would be very careful doing anything with kilo-volts using a circuit, as opposed to a static charge device, such as Van de Graaff generator.

When you get shocked by a Van de Graaff generator, you do get high voltage, as well as high currents. The missing ingredient is time. The shock takes a very small time, so the energy delivered by the shock is very small. Skin-effect also helps.

Relevantly in the case of microwave oven transformers, your impedance depends on the voltage because a high enough voltage can and will arc right through your skin into your soft, low-impedance innards. You can do this safely with a commonplace Tesla-coil-driven consumer plasma globe by putting just enough aluminum foil on top of it to arc through your skin, leaving cute little black charred spots, but in short enough bursts that it won't stop your heart.

You haven't explained anything unsaid in this thread, including by me, but merely completely ignored my argument that there are far more hazards with electronics than merely fatal electrocution.

What they're getting at is that while it is the amount of amperage that goes through your heart that determines your likelihood of dying, you need a certain voltage to overcome the resistance of your skin to achieve such an amperage. Anything under around 50v is generally safe to touch, and often high amperage applications are under that limit.

So the reason high voltage is more dangerous, if it has sufficient amperage backing it up, is that the higher the voltage, the better its ability to pierce your skins resistance and flow through your body to begin with.

It's the Ohm's law: V=IR. Amps (I) kill you but your body has rather high resistance, at least kilohms (even when wet), and it depends on the voltage partly. So low voltage even with high amps current do nothing to you.

And the corollary is high voltage with low amps do nothing to you too, neither amps nor voltage kill you alone.

The issue is that low voltage is guaranteed not to shock, can burn of course.

High voltage is inherently dangerous.

High voltage is not inherently dangerous. In a dry climate you can easily develop ten thousand volts by lying down in a bed without bedsprings with a long acrylic blanket and pulling the blanket over your head hair with your feet. You can get multiple-centimeter-long branching sparks of static electricity from your finger. The only danger of the activity (to you) is that you might produce enough ozone to irritate your lungs. But the energy of those sparks is limited by your body's capacitance to the blanket.

If you do this in a vacuum you could get X-rays, and if you do it near your cellphone or laptop you can kill them. But it's not dangerous to your body.

However, high voltage with enough power behind it to burn a Lichtenberg figure through your body can kill you pretty darn quick.

electronics die off ESD w/o the xray. I didn't mentioned ESD on purpose as indeed what really matters is energy/joules. If you have a source capable of high power but for too short time it won't be that dangerous either.

Thanks for clarifying, I didn't mean to imply that X-rays were necessary to kill electronics with ESD, just that they could be dangerous to a human, physically, even at low power levels. Killing electronics with ESD indeed does not require vacuum.

An analogy: while technically what kills you due to a fall is called “gravity”, that’s not the whole picture. In actuality, it’s the height you fall from, which allows gravity to build up enough velocity to kill you when the fall ends.

Despite the fact that you’re experiencing the same gravitational acceleration from both, a one meter fall, while being potentially dangerous if you’re not prepared and allowed to land right, is not likely to kill you. A 100 meter fall, on the other hand, is likely not survivable by any means.

This seems like the opposite situation. Gravity doesn’t kill you from a fall (just like voltage doesn’t kill you from electricity). Gravity makes possible the sudden acceleration that kills you, which is analogous to the voltage-induced current.

The ground technically kills you. People have fallen for months, even over a year, without harm

I dont know what they did in the uni, I thought it was some wielding or power delivery (CPU and GPUs nowadays deal with 200A+)... So I honestly thought it was high amps, all of them are proper fire hazard.

But you are right, likely it was high voltage.

Maybe they meant high voltage amps

Once I charged a 1F (not a typo) capacitor with either a AA or 9V battery (can't remember), then touched the leads.

Youch!

You must have charged it through some step up device, otherwise the max voltage on the cap is the battery voltage which isn't going to shock you.

Maybe they pinched the leads together between their fingers. That could be painful.

I'm glad you assumed a very limited scope of danger being direct electrocution death because in my class I learned there are many compound forms of electrical accident. To quote NEC textbook:

"Even low-voltage installers can still experience unsettling shocks, especially if they are working in an unsafe environment, such as if they are ungrounded or standing on a wet spot,” Johnston said. “While it’s unlikely that such shocks will cause serious injury by themselves, they certainly could literally knock someone off balance, which could be a real safety risk if an installer were standing on a ladder.

“In addition, an arc in a low-voltage system has the same potential for igniting explosive materials as one in a 120-plus-volt system. Chapter 5 of the NEC provides rules for installing electrical wiring of any voltage in a hazardous (classified) location, specifically those locations with high concentrations of flammable or combustible liquids, flammable or combustible vapors, conductive and combustible dusts, and so forth.”

It's also possible for low voltage shocks to cause your hand muscles to seize the hazard and be unable to release it.

In fact, my TENS unit, specifically designed to cause muscle contraction, runs on 9V.

Edit: ah... I see a throwaway account was used, so you will never have to confront your mistake. I wish these were banned.

I cant see how 9v dc can shock you aside touching the leads with tongue... or using any step up electronics.

As a kid we used to test batteries voltage with the tongue, 9V had a distinctive bite, compared to 4.5V. Even today I can tell the output voltage of a multimeter (in its ohm mode)

Lastly, I would encourage you to consider tasers, which deliberately deploy (nonlethally) upwards of 20K volts for multiple seconds.

Yeah, usually when someone parrots the "it is the amps that kill you, not voltage" line, I have to remind them that the amps depends on the volts.

A car battery is capable of hundreds of amps, but if you touch the contacts with your hands, you won't feel a thing, because the voltage is too low to overcome your body's resistance.

I imagine if you wired the leads to your tongue, your tongue would probably explode though.

It's advisable to remove rings if there is any way they could short across a car battery. The battery has very low internal resistance, so you can get a sizeable part of a kilo-amp flowing, which due to "P = I^2 R" can generate an impressive amount of heat. In fact some owners of certain Russian motorcycles with a propensity (Ural, Dneipr etc.) were able to weld bits back on in the field by using the carbon contact breaker points to do rough arc welding.

Which doesn't contradict you at all - I'm just saying treat car batteries with respect.

lmao you couldnt figure out how to turn off your tv... spoilers, hold the power button for 2 seconds.

I think the people replying to you to nitpick are missing the forest for the trees.

You (and many people) have to wait until university to learn this stuff if you didn't seek it out yourself (how-to's and electives in school). This kind of knowledge should be taught at a young age to demystify it.

A few hours in uni (and how many people never even go), to learn life-saving information

When I did appliance repair microwaves were treated as bombs. You didn't test your components live, you always unplugged first, etc.

Still walked into another tech working on one (cabinet-mounted up high), with the cover off, barely on a wobbly stove-dolly and his expensive Fluke multimeter out with leads in hand.

I noticed the plug still lifted up into the cabinet so I peeked in and sure enough it was plugged in.

Big red warning signs on the power cable, the covers inside and the cover outside all had warnings. Dude had been through the same training I had, and still thought it was a good idea. "I'll just stay away from the high side",he said.

edit to add this microwave had an external fuse. All you had to do was unscrew it and check the fuse inside- which was bad. He hadn't had to do any of the stuff he'd done prior to my arrival. They'd had an electrical surge when the power had gone out and the fuse had caught it. This tech had been on the job longer than I. end edit

Even people trained and with knowledge make mistakes and sometimes are just plain stupid.

People without knowledge can be dangers to themselves and others.

Texas had a rash of house explosions a few years ago from people raiding copper and power wires from empty houses with live gas lines.

I think the answer is educating and many people as possible, from as young an age as possible.

A friend of a friend disassembled a microwave to repair it, and accidentally put one of the radiation shields back on backwards. It ended up killing his wife (lots of cancers) a few years later.

So, yeah. Don't repair microwaves. It's really not worth the $100's you'll save on a replacement.

How would he know the microwave was the cause?

Why was the cancer attributed to the microwave incident? After all, it's not ionizing radiation.

Ultraviolet light causes skin cancer, yet it is not ionizing.

https://en.wikipedia.org/wiki/Non-ionizing_radiation#Lower_f...

From that link:

> “2011, the International Agency for Research on Cancer (IARC) from the World Health Organization (WHO) released a statement adding RF electromagnetic fields (including microwave and millimetre waves) to their list of things which are possibly carcinogenic to humans.”

WTF. This was the exact opposite of my understanding until today… ie that non-ionising radiation from the likes of microwaves was not carcinogenic.

I don’t know how to keep up with this stuff.

Possibly carcinogenic. Some things we know for sure are carcinogenic, but even then what we know is that exposure increases risk in a population by so-and-so percent. It's much harder to work backwards from one individual case of cancer and finding out what the cause was.

It's highly irresponsible and downright cruel to accuse the husband of killing his wife by botched microwave repair based on so little evidence.

What was the location and extent of the original microwave injury? Did the cancer originate in the same spot? What is the proposed mechanism of action? How long is "a few years later"? Can it be ruled out that she didn't have cancer at the time of the microwave incident? What other causes has been considered, other known carcinogens, or a family history? Who made the claim in the first place, did the oncologist blame the husband?

Yes completely agree regarding blaming the husband. Without the - likely unobtainable - certainty that that was the cause, why even suggest that…

Near UV isn't, but the photons still carry considerable energy to push chemical reactions over the edge. Whereas microwaves are far, far below the visible spectrum, and none of that causes cancer.

A microwave injury is serious stuff, but it seems like a huge stretch to attribute a later cancer to that exact incident.

> Near UV isn't, but the photons still carry considerable energy to push chemical reactions over the edge.

In my opinion (I am an amateur biologist) there is no need to deploy considerable energy to mess things at the cell scale: Most interactions there occur because of thermal noise.

Furthermore most protein interactions depend how they are folded which involves different fields, including Van der Waals forces. Van der Waals forces carry an energy of 4 to 40 meV per bond which is in infrared range.

So even infrared can mess up the internal working of cells. It could be that even lower frequencies also have a biological effect:

(Non-thermal effects of radiofrequency electromagnetic fields)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7417565/

Yet cells have many "quality control" mechanisms so usually the is no permanent damage.

But infrared exposure could bring benefits to cells also.

Wait until more DIY EV servicing videos start appearing. If you short something across a decent size EV battery it will be converted into plasma and deposited on your face.

where your face recently was.

EV is DC, and DC sparks are a thing of beauty as they lack self-extinguishing properties unlike AC sparks.

why is that? I couldn't find any info about this

50Hz AC drops to zero volts 100 times a second, which makes the arc easier to extinguish. "Self-extinguishing" is a deadly exaggeration, though, as you know if you've ever seen a high-tension line being connected or disconnected. Arcs are only self-extinguishing when they deplete their energy source or destroy what they're arcing to.

Caveat: I'm kinda dumb and this is a Cunningham's law situation.

tl;dr Because in a DC situation the current is always high so the temperature through the air is always high so the air remains a plasma and remains a good conductor the whole time.

OK I = V/R is how we talk about currents. Current (I) equals the potential (V) over the resistance (R).

An electrical spark is where the potential across an air gap is high enough that the air—normally a good insulator and thus a poor conductor—breaks down into plasma. In that state, the air is hot enough that the electrons that would be bound to the atomic nuclei can flow the way electrons in metal do. This means that the resistance of that air gap goes from being a high number to being a low number.

In the case of a DC spark, we have a constant high potential and with the plasma state a low resistance, so I = V/R = big/small = big current. Since we are putting a high current through a conductor, the temperature of the conductor goes up, and the plasma remains a plasma. It stays a good conductor the whole time.

In the case of an AC spark the AC potential goes from some big positive number of volts, to zero volts, to some big negative number of volts, to zero volts, to some big positive number…you get the idea. At some point I=V/R goes from being big/small to zero/small, which can be long enough for the air to cool off and stop being a plasma and be a bad conductor. So when V is a big (positive or negative) number again in 1/4 of the period of the signal (probably 1/60/4 = 1/240 seconds) the air might be too cool to conduct the current. Then V/R would be Big/HUGE = effectively zero current.

Remember: I'm just some weirdo online. This is not advice. Don't mess around with electricity.

> Not to mention, the burnt wood looks so gaudy and uninteresting. I would hardly call it fractal as it only goes 2-3 levels usually, and artistically doesn't usually make sense on furniture etc.

There's some point I could make about how this is the worst art anyone has ever died for in history, but we'd end up in the weeds.

I'd be interested in trekking through those weeds.

Anyone have a contender for worse deadly art?

My weeds were a bit more like how in our current cultural moment our (US centric) romantic ideas are now their worst versions. Entrepreneurship: join an MLM or become a crypto weirdo or try to start a drop shipping business as advertised in a YouTube preroll ad; Self sustenance: make a bunch of consumer choices that mark you as an individualist while doing nothing to make yourself self sustaining; political engagement: be a shitposter or maybe become a conspiracy freak since it's mainstream now; passionate self expression: die making high effort, high risk, zero reward, looks-worse-than-woodburning-by-a-mile arts and crafts that are on top of it all incredibly cliché.

At least Luis Jiménez's deadly mustang sculpture looks cool!

Electronic -> electrical

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