Electric shock

[mark3141]

IF this chap was using a voltmeter how did he come so close to killing himself?

[Rerouter]

he had it on amps.... 

and his ground connection must have been poor enough that it took the few seconds to pop the fuse, with the wiring out of the device holding the voltage high enough to cling him on there,

[mark3141]

Hmm... yes that would do it.

He used the "moment of inattention" defence — but his seemingly random poking around mains voltages seems terrifyingly dangerous...

[BillyD]

Shouldn't be wearing metal jewellery around live electrics either.

[jucole]

Poor chap! I'm not sure he knows himself what setting he had his meter on, but there's a nice MOS 6502 in what looks to be a commodore floppy drive though.

[Rerouter]

if anything this may make him respect mains a bit more, i for one never work live unless its the only possible way, and when i do need to, keep on a non conductive mat with one hand in a pocket or a glove, cause once it bites, its got you and your not moving,

also i seriously have to wonder why it took so long for his fuse to pop, the meter measures across what 0.1 ohm? plus another 1.5 for both meter leads, that leaves about another 20 ohms unaccounted for... that or it was grossly over-rated or self wound with wrong wire, considering he doesn't have ground fault current interrupters or residual current detecting outlets it would put the house in that vintage

[mark3141]

Has Dave ever posted a piece on safety — along the lines of "Really stupid things to avoid doing at all costs"?

To prevent my last mistake becoming my final mistake.
Might be an idea...

[Rufus]

he had it on amps.... 

Not much makes sense in the video.  This looks like a service manual for what he was playing with

http://wiki.classic-computing.de/images/0/07/1540%2B1541_SERVICE-MANUAL.pdf

The plug he poked the meter probes into has two secondaries from the transformer - no mains.

The chassis appears to be a single folded metal sheet so there is no way he would be shocked by holding onto either side of it.

IMO either he has given an extremely poor depiction of what he actually did or it is just made up bullshit.

[BulletMagnet83]

Having cocked up quite a few times and touched something I shouldn't as an electrician's mate a good few years ago, part of me doesn't believe what he said he did could have had the effect reported. I'm not, and most likely never will be, an expert.... but I've had enough shocks to know that if there's a properly-working RCD on that circuit, you get a jiggle and say a few naughty words then the supply gets knocked out and everyone has a good laugh about it on teabreak.

I also doubt the muscle lock-up thing... for AC anyway (I always thought it was HVDC that did that, though I welcome any corrections!). Again only going on my own experience, a mains AC shock felt like intense vibration together with something like a cross between a nettle sting and hitting your funny bone, then jerking away from it. Not something I'd do on purpose, but with functioning RCDs/RCBOs on the line, not the end of the world and certainly not video-worthy.

That said, I do love my retro computing porn, so have subscribed to the chap's channel anyway!

EDIT: In case it sounded too much like I was making light of a potentially serious hazard, I did (eventually) learn, and get some proper 1kv insulated gloves for work that required things to be tested live.

[c4757p]

He's bullshitting. No way that plug has mains on it, and apparently he didn't get shocked until he had *both* hands on the same shielding plate? 

[david77]

he had it on amps.... 

Not much makes sense in the video.  This looks like a service manual for what he was playing with

http://wiki.classic-computing.de/images/0/07/1540%2B1541_SERVICE-MANUAL.pdf

The plug he poked the meter probes into has two secondaries from the transformer - no mains.

The chassis appears to be a single folded metal sheet so there is no way he would be shocked by holding onto either side of it.

IMO either he has given an extremely poor depiction of what he actually did or it is just made up bullshit.

This.

That guy hasn't got a clue what he's talking about.

[millerb]

I got the worst shock of my life working on a neon sign. I was holding the metal bars that prop up the tube structures with my left hand while screwing with some connecting wires with my right hand... The transformer was putting out 8,000V AC. I couldn't let go of the damn thing even though I tried with all I had. What saved me was falling backwards out of my chair. I'd probably be dead if I fell over on to it. AC can definitely lock up your muscles.

[c4757p]

A thought: would this thing have filter caps mains-earth? Perhaps for some reason during his probably very unintelligent jaunt through its internals, he disconnected the earth. Then he got a little nip out of the filter cap and he's exaggerating the hell out of it.

[BulletMagnet83]

A thought: would this thing have filter caps mains-earth? Perhaps for some reason during his probably very unintelligent jaunt through its internals, he disconnected the earth. Then he got a little nip out of the filter cap and he's exaggerating the hell out of it.

If so, he should probably never play with any disposable cameras, he'd probably piss his pants.

Millerb, yeah I bet!  8000VAC is something I hope to never experience, and I have no trouble believing that WOULD lock up your muscles... I just reckon 230VAC normally wouldn't, especially with some fault protection on the circuit.

[c4757p]

They're fun, aren't they? That was my first electric shock ever 

Didn't he say something about an earth lead being available when he was working on it? I think he did disconnect it...

[BulletMagnet83]

Haha yes, they are fun. My first teardown was a flash camera aged <10, and guess who didn't discharge it before handling the board? Still, playing with those, and cap discharge pyro igniter circuits based on them, taught me one valuable lesson - never EVER give in to temptation and buy huge 4kV pulse discharge caps from eBay... no way I can be trusted with them! A 2J discharge hurts more than enough.

[c4757p]

I'm too much of a pansy with high energy stuff. I wouldn't go near them lest they become demon-possessed, go crazy and bite me. HV by itself doesn't bother me, but the capacitors that are measured in the volume of shit you lose if you accidentally discharge one are not something I'm fond of.

[BulletMagnet83]

Yeah, that's one area I'm more than happy to watch on Youtube rather than attempt myself. Still, I think it's fair to say most shocks I've had, I've been able to laugh about afterwards... That makes me feel lucky though, rather than complacent. Small mistakes we can walk away from serve to make us better in the long run

[G7PSK]

I had a shock from an 1980's 22 inch colour TV HT. It knocked me across the room and 9000 volts from a mains powered cattle fence energizer, straight from the terminals lifted me off my feet, both times it felt as though all the bones had been pulled from my arm and then snapped back.

[c4757p]

The worst I've had was ~600VDC out of an oscilloscope. Came pretty close to giving myself a good one off a CRT flyback transformer, though - I was playing around with a CRT, trying to get it to work, and must have been touching something without realizing it had HV on it. Luckily it was shut off by the time I touched my oscilloscope and discharged into the BNC. I had quite a bit of charge built up on me...

[ptricks]

I have gotten shocked by AC and DC, DC took longer for the pain to go away. I started my career when CRT TV were the best tech  and that meant working with the giant capacitors that are CRT , they can remain charged for years after last use.  The worst part was that on most sets everything inside the case was live, even touching something like the wires to the speaker could give you a shock. Most sets produced  165VDC for the boards main supply. 

[orbiter]

@ 4:20 he mentions that he couldn't let go of the device because it was running on AC. He then states
that 'once AC has got you, It's got you and you have to be pushed off it'!

[duskglow]

Those live chassis televisions were awful.  I still am surprised I never really got shocked.  I must have been remarkably paranoid for a ten year old.   

[IanB]

Carpet doesn't conduct electricity. So you could poke something through the grille and touch a live part and most likely you wouldn't feel a thing...

[cthree]

My worst shock was from a telephone patch panel. The shock was getting a shock from a phone line, the pain was intense, like a hundred bees stringing me in the finger all at once. I must have touched 48VDC ringer voltage. No buzz like with AC.

I've been zapped with AC mains many times. They say you can't let go? Bullshit! You touch a live mains hot wire and you'll yank your hands out of there real quick! It happens all the time and very few people suffer any lasting effects. There aren't enough ambulances.

That said, play safe!

[cthree]

Also, the voltage on the mains is at or near zero a good percentage of the time.

[807]

I can't make head not tail of that video!

It looks like he grabbed hold of the chassis with both hands. Whether the chassis had mains on it or not, it wouldn't conduct through his body.


...and it blew 2 fuses! How much current flowed through him!

...and he said that he should have had the meter on amps instead of volts. Why? What was he trying to measure? How did having the meter on volts contribute to his shock?

I also thought that it was DC that locked up your muscles, not AC at mains voltages.

[cthree]

I bet he got shocked with DC which is at 100% potential 100% of the time and that hurts like a mofo and can really ring your bell.

That connector in the video has two red and two black wires. That's switched DC, probably 12v and 5v. He probably bridged the 12v DC to the metalwork with the exposed positive probe sticking out of the connector. When he grabbed the metalwork he must have caused a short between the metalwork and chassis ground. The metalwork is probably grounded throughout that connector. By removing it he left is floating, allowing the metalwork to become energized.

I don't think it has anything to do with the multimeter unless he has it in amps and was energizing the metalwork with the negative lead. The dmm would have a slow blow fuse so you could get a nasty jolt before the fuse blew and it may not have blown at all depending on how many amps were flowing and for how long. 10 amps at 12 volts would do it and it wouldn't blow an 11 amp fuse.

It wasn't AC mains. AC is uncomfortable, not painful. DC is and if you don't think you can get shocked with 12 volts, go out and touch the terminals on your car's battery and then report back with your findings

That's my theory anyway. Don't care to study it in any more detail.

[807]

I bet he got shocked with DC which is at 100% potential 100% of the time and that hurts like a mofo and can really ring your bell.

That connector in the video has two red and two black wires. That's switched DC, probably 12v and 5v. He probably bridged the 12v DC to the metalwork with the exposed positive probe sticking out of the connector. When he grabbed the metalwork he must have caused a short between the metalwork and chassis ground. The metalwork is probably grounded throughout that connector. By removing it he left is floating, allowing the metalwork to become energized.

I don't think it has anything to do with the multimeter unless he has it in amps and was energizing the metalwork with the negative lead. The dmm would have a slow blow fuse so you could get a nasty jolt before the fuse blew and it may not have blown at all depending on how many amps were flowing and for how long. 10 amps at 12 volts would do it and it wouldn't blow an 11 amp fuse.

It wasn't AC mains. AC is uncomfortable, not painful. DC is and if you don't think you can get shocked with 12 volts, go out and touch the terminals on your car's battery and then report back with your findings

That's my theory anyway. Don't care to study it in any more detail.

Zilch...nada...nothing...not a dicky bird...not a tingle! LOL.

Just been Googling AC & DC shocks & was surprised to find that AC also contracts muscles. I have always thought it was just DC.

[smashIt]

 

[c4757p]

Shocked by 12V? Yeah.... no. I've touched a car battery many times - nothing. Just to humor you, I just asked my power supply how much voltage it takes. This is with wet fingers, and yes, I took my hands off and replaced them - no frog-boiling here: 32V before I could feel anything, 38V before it was anywhere near uncomfortable, and 54V made me jump. I could just feel 12V on my tongue.

[cthree]

Zilch...nada...nothing...not a dicky bird...not a tingle! LOL.

LOL. It only counts if you actually do it. Math is for cowards

[richard.cs]

Shocked by 12V, do-able but unlikely. I've poked copper strands into my skin while working on a car and once you take out the resistance of the skin you can pass enough current for a painful shock on top of the general unplesantness of wire in the finger.

[ddavidebor]

At 12 in the worst case you may feel a little disturb if you concentrate

[kolbep]

Normally, to check if a 230v circuit is live,  I hold one of the dmm probes by the metal, and probe with the other probe. Times like that I am not worried aboutv exact reading, just that it is live. (With my body impedance, and the high impedance of the dmm, I do not feel a thing, even though the dmm shows up to 190v

DId that today again, but my dmm was on ohms. Ouch. But I am used to it.

[c4757p]

Normally, to check if a 230v circuit is live,  I hold one of the dmm probes by the metal, and probe with the other probe.

[richard.cs]

Normally, to check if a 230v circuit is live,  I hold one of the dmm probes by the metal, and probe with the other probe.

GENIUS

It's not *that* bad, comparable to the use of a neon screwdriver. Except the neon screwdriver doesn't have a low impedance setting (unless you stir your tea with it) and therefore has less opportunity for screwups like the one described.

[c4757p]

Except the neon screwdriver doesn't have a low impedance setting

Say that again a few times.

[richard.cs]

Except the neon screwdriver doesn't have a low impedance setting

Say that again a few times.

Unless you damage it or get it wet a neon screwdriver will always put a few hundred kilohms between you and the mains being tested. A DMM may inadvertantly be set to resistance or current and place neglidgable impedance between the two probes.

Ok so perhaps the word "setting" is misleading, but the point is still valid and to me at least it makes sense to use the word when comparing to a DMM.

[c4757p]

No... I meant that the DMM is nowhere near comparable to a neon screwdriver in safety. The screwdriver cannot be set to a mode where it fries you. You have to damage it for that. The DMM is one accidental click of the range selector away.

Perhaps I sounded a bit too snarky. I just meant that I think you overlooked how important that sentence was.

[richard.cs]

I just meant that I think you overlooked how important that sentence was.

I think we're in agreement then. I wouldn't personally test with a DMM in this way (although I have been known to do such tests with the other end stuck in the ground or poked onto a convinient earthed screw) but when used with care it is in principle safe, even if the potential for lethal mistakes is much greater.

Having destroyed a few meter shunts with similar mistakes in the past I wouldn't trust myself not to make the same mistake when doing dodgy voltage testing.

[BillyD]

I just meant that I think you overlooked how important that sentence was.

I think we're in agreement then. I wouldn't personally test with a DMM in this way (although I have been known to do such tests with the other end stuck in the ground or poked onto a convinient earthed screw) but when used with care it is in principle safe, even if the potential for lethal mistakes is much greater.

Having destroyed a few meter shunts with similar mistakes in the past I wouldn't trust myself not to make the same mistake when doing dodgy voltage testing.

Now that is a bloody good point! I've done the same, and blown a few fuses in my time by forgetting to configure the meter back to voltage - but happily I wasn't part of the circuit on any of those occasions!

[MacAttak]

He's bullshitting. No way that plug has mains on it, and apparently he didn't get shocked until he had *both* hands on the same shielding plate? 

I don't see where those plates are clearly electrically connected. Can't assume them to be at the same potential.

[MacAttak]

Has Dave ever posted a piece on safety — along the lines of "Really stupid things to avoid doing at all costs"?

To prevent my last mistake becoming my final mistake.
Might be an idea...

It's come up before, but several reasons for not doing it.

• Some things aren't always safe or always dangerous.
• There are differences in what is safe in different parts of the world - especially when it comes to mains power.
• As soon as you post safety information, you can bet some idiot will misinterpret it, maim himself, then try to sue you.
• In most cases, the only way to truly be safe is to know what the hell you are sticking your fingers, probes, or soldering iron into.

[houdini]

I think photonicinduction showed that those screw drivers can be extremely dangerous.

[duskglow]

He did.  But in fairness to the screwdriver, he could probably make a bowl of jello dangerous.

That's not to say you're not correct.  They are dangerous.

[mark3141]

I take your point MacAttak.

However I still think some general advice might be useful to prevent damage to me or my test gear.

As for Photoinduction I always take his safety advice seriously.
A man who does what he has done — and is still alive — clearly knows that he is doing.
Of course when faced with a pool of burning petrol I still probably wouldn't get out the Dyson and start vacuuming ...

[tec5c]

Reminds me of this video....



Wouldn't you just love to have this guy "repairing" your tv??? 
Pull out a bare processing (timing control) pcb, place on ESD protected? surface (a remote), fumble with a multimeter, then put the pcb back in your tool kit, ensure the tv is ON and then proceed to test for continuity. Good form!

[Bored@Work]

Wouldn't you just love to have this guy "repairing" your tv???

Must be a member of this forum. At least his work is consistent with the repair and hacking advice you get here.

[nukie]

Sometimes when your muscles is electrocuted they tend to stiffen up and you lose control over them. That's when things gets out of hand.

[Spunky]

There seems to be a fair bit of confusion here about AC, even about whether or not it can harm you.

Firstly current, 10mA is enough to make you grip something and not let go, 30mA (if it passes through the heart) can kill you.

Voltage, 50VAC is considered dangerous, at above 400v the skins resistance is overcome and you start conducting internally, and around 600 to 1000v you start to burn (depending on current too of course).

Those screwdriver tester things are a joke, most of them don't even have a fingerguard. Best to buy a voltstick or test with a decent multimeter. And yes carpets do conduct electricity, and no the fact that AC is at zero potential some of the time won't save you.

A GFCI, ELCB, RCD, RCBO, RCCB etc is probably your best protection. But don't expect it to work if powered from an inverter or generator.

[dfmischler]

The worst I've had was ~600VDC out of an oscilloscope.

I remember two incidents from my early teenage years.  I remember playing with the telephone line where it entered my parents' house (tapping it?  adding an extension?) and stripping the wires with my teeth (!) when the phone rang.  I can assure you that CO ring voltage (80+ V RMS) in your mouth is quite unpleasant.  I think that is the incident that got me to stop stripping wires with my teeth.

When I was about 14 I once built a battery operated relay oscillator circuit and hooked it up to a reversed line transformer and found that I could draw an arc well over a centimeter long.  I was playing with it and was zapping bugs or something and, trust me on this, even a very low current low duty cycle high voltage arc really hurts.

[G7PSK]

Voltage hurts, current kills. It really does not matter whether its AC or DC.

[ResR]

I had also nasty experience with electricity. It happened at my workplace, when I was scheduled to do electrical repairs&cleanup in section P-6 of the pig farm. The electrical system is like it is from early 1980's with almost no maintaneance done past 10 years before I got there, nobody knows where the circuit breaker is and I had no idea, that the neutral is going through the switch and live is straight into the lamps. My voltage tester was also buggy and didn't show presence of the voltage at the moment. So I took a wet rag and start to clean off the fly s**t from the 36/40W T8/10 fluorescence tubes, it was so much that the 3/4 of the light was filtered out by it. It was fifth lamp, russian T10 tube. I almost cleaned the whole tube until I made it to other end metal cap with 2 electrical pins and I got my hand stuck on 230V 50Hz, current path from my hand to my legs into metal ladder. I fell backwards (I would died if I fell onto the ladder), ripping the bulb out of the soviet era fixture, breaking the socket in progress, fell down 2,5 meters onto the concrete floor centimeters from the pig cage steel sheet wall. I must had some sort of guardian angel, but I survived it somehow. It took me whole week to restore to normal capability.

[Spunky]

Switched neutral wasn't legal even in the 80s. But then in the 80s any farmer was allowed to do his own electrics so who knows what you might come across.

[ddavidebor]

different country has different law.

for our europeans, USA laws for electricity in house is just a bad joke

[Monkeh]

Switched neutral wasn't legal even in the 80s. But then in the 80s any farmer was allowed to do his own electrics so who knows what you might come across.

Farmers still can do their own electrics, as can you and I.

[WarSim]

Switched neutral wasn't legal even in the 80s. But then in the 80s any farmer was allowed to do his own electrics so who knows what you might come across.

Farmers still can do their own electrics, as can you and I.

In all the countries I have looked into. 
Detached freehold yes.
Coop/Strata/communal/leased no.
Attached freehold,common-hold maybe.

[Corporate666]

The worst I've had was ~600VDC out of an oscilloscope.

I remember two incidents from my early teenage years.  I remember playing with the telephone line where it entered my parents' house (tapping it?  adding an extension?) and stripping the wires with my teeth (!) when the phone rang.  I can assure you that CO ring voltage (80+ V RMS) in your mouth is quite unpleasant.  I think that is the incident that got me to stop stripping wires with my teeth.

When I was about 14 I once built a battery operated relay oscillator circuit and hooked it up to a reversed line transformer and found that I could draw an arc well over a centimeter long.  I was playing with it and was zapping bugs or something and, trust me on this, even a very low current low duty cycle high voltage arc really hurts.

LOL!  I did almost the same thing.

I was into electronics as a kid, and offered to wire up a new phone line in my sisters room.  So I run the wire, and before I connect it, I figure I'll test it.  I stick the two wires in my mouth on my tongue, and my sister goes to living room to call the new line from the old one.  That rang my bell for sure.  For some reason, I thought phone lines were low voltage.

[Corporate666]

different country has different law.

for our europeans, USA laws for electricity in house is just a bad joke

Huh?

I've traveled extensively in Europe and I've seen some shocking (pun intended) home electrical work there - stuff that would have the cops at your door in the USA.

[c4757p]

On the telephone line note: When I was a little kid playing around with electronics, I discovered that if I put a speaker across the telephone line, I could listen to it. I'm not 100% sure what happened (if I understand how the lines work correctly, the low impedance should signal 'off hook', so it shouldn't ring), but it rang. I'm not sure what impedance that highish-voltage ring signal comes at, but I'm pretty sure I shit myself...

That was the end of me messing with phone lines.