Electric shock

[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.