A shocking discovery

[Pentium100]

Would you open the cover on a plugged in power supply that was running (maybe with even a label that says "DANGER: HIGH VOLTAGE INSIDE") and touch the exposed capacitor terminals or transformer connections?  No, you'd unplug the device and de-energize the caps first.

Forget the power supply. Turn on a TV (or a monitor), remove the cover (disregarding the warning) and stick your finger (or an all-metal screwdriver) behind the anode cap. 25-30kV is more fun than 0.22kV. Somewhat insulated screwdriver will also work, but you will lose some of the voltage in the insulated handle and nobody wants that.

[Shale]

Pro electricians work on live wires all the time. I did on several occasions when repairing gas stoves.

Well, until you come across a place that was miswired (so the wire that's supposed to be neutral is actually live) or somthing causes you to touch the live and neutral wired at the same time.

The way I see it, there is no real reason not to turn off the power when working on an outlet (or a switch). On the other hand, I may poke around in a device with the power on in order to repair it (no way to measure the voltages if the device is turned off).

When I used to work on generators. I worked on Live 480 on a semi regular basis. As long as you take the proper safety precautions is not to big a deal. I worked around a lot of exposed 480, just part of that business.

On a side note, i have been working on a home with 120 and grabbed a common that was hot. So been there, done that, not so fun, but lived to tell about it.

If you have the chance to turn off the juice, then do so, but some times its not possible, and other times when working on mains, its just not convenient to turn off the juice. Ya I'm sure some one is gonna get upset and say there is always time to for safety and you should always turn off the juice. But in reality when working for an employer and the breaker to a circuit is across a building and down in the basement and your working on the 10th floor, its just not practical in some situations. So you may just wire up some little 120 plug, or 480 on some relay hot. I try not to make that a practice, and I take extra time a precaution when I know I am working with something that is hot, but it happens.

[IanB]

Half the trouble with working "hot" is those loose ends of live wires floating about. Sure, you can cap them to prevent them touching something, but you still have to remove the cap to connect them to a terminal, and during that exposed interval they might touch something they shouldn't and short out (or touch you and make you jump).

I just spent the whole afternoon mapping out my house and figuring out which power outlets are on which breaker. And wouldn't you know it? Half the outlets I want to replace with new ones are on the same circuit as my computer. Which is a pain, as I never shut down my computer unless I really have to. Looks like I will have to... (shut it down again that is, not counting this afternoon's experiments)

[Randall W. Lott]

And one more thing: are you meant to mount the socket with the ground pin "up" or "down" (as pictured)?

I have some low profile plugs where the cable falls downward with the ground pin below, and others where the cable expects the plug to be inserted in the opposite orientation.

The most common convention seems to expect the ground pin downwards, but the manufacturer's installation diagram suggests the opposite.

I wish people would make up their minds.

They suggest ground pin up.  Naturally, your thumb will tend to contact the top of the plug when handling it.  I like them on the bottom because that's what I'm used to and I don't plan on handling plugs by their blades.

[ronwoch]

^^ WHY oh why do we feel the need to protect people from themselves?
Outlets in this country have been like that for many, many a decade. I dare say that if it were such a HORRIBLE safety concern, then our population would be significantly less. Are there better, safer designs out there? Sure. But really, let's think it through. Good parents teach their children not to touch a hot stove, a heater, or stick a penny or anything else into a socket. There are plug protectors for when the child is too young to grasp the point.
Simple. DON'T touch that or it can hurt you. After they touch it anyway, the child is quick to learn that mommy or daddy was right. And they don't do it again. Also, it reinforces the concept that if mommy/daddy says that messing with something can hurt, it will!
I'm only 26, but of all the many wall sockets I've seen in my life, only a few have had cracked faceplates. And ya know what? It still prevents you from touching the live wires! So 'flimsy' or not, THEY WORK! If it is so badly damaged that it DOES allow access to something dangerous, it takes a buck or two at the hardware store and a few minutes with a screwdriver to replace the damn thing.
THIS is why lawyers make money suing companys like mcdonald's for not putting HOT COFFEE on the outside of a coffee cup.
I mean, REALLY?!
Ugh.
/ranting

[Zero999]

Forget the power supply. Turn on a TV (or a monitor), remove the cover (disregarding the warning) and stick your finger (or an all-metal screwdriver) behind the anode cap. 25-30kV is more fun than 0.22kV.

Apart from the fact it's now 2012 and old CRT monitors are no longer made. The 25kV inside a CRT is much less dangerous than 230VAC because the current is limited to under 5mA and the anode capacitance is under 100pF

[PeteInTexas]

There is nothing shocking about this at all.  What's next: "Shocking discovery!  Stripping insulation exposes live wires!"

[Simon]

As i understand it, removing a wallplate is not something a typical person is supposed to be doing.

If safety rules were about what a typical person is not supposed to be doing, then most of the safety rules in existence would be unnecessary. Nobody should be doing anything dangerous.

But here's the story with wall outlets in the USA.

This is what the fixture looks like in the wall (cover removed with one simple screw):



And close up, here is the fitting outside the wall:



All the exposed metal parts on the side are live. The opposite side is exactly the same for the neutral wire.

Here is a natural way to grasp it when removing it from the wall. Note how the fingers naturally fall on the live metal terminals. I am sure nobody has been required to produce any kind of safety case for this design.



(It looks like the old fitting in the wall is a tiny bit safer than the new replacement...go figure.)

I can't see a huge problem with that and am a firm believer in natural selection. I was wiring in Italy when I was a kid and got no formal training (as if the itis know what elecytrical safety is) and used my common sense and huge respect for a voltage that was 4-5x what is defined as lethal.

[siliconmix]

I can't see a huge problem with that and am a firm believer in natural selection. I was wiring in Italy when I was a kid and got no formal training (as if the itis know what elecytrical safety is) and used my common sense and huge respect for a voltage that was 4-5x what is defined as lethal.
[/quote]
am a firm believer in natural selection pmsl.
working on live stuff.i had to kick a sparkey off a bread packing contraption once .he was stuck to it  he was covering the red emergency switch which i couldn't get to.he was ok though because he said he was expecting it anyhow.

[Simon]

haha

[Pentium100]

Which is a pain, as I never shut down my computer unless I really have to. Looks like I will have to... (shut it down again that is, not counting this afternoon's experiments)

Buy a UPS. It will also help keep the computer up when the power fails.

Apart from the fact it's now 2012 and old CRT monitors are no longer made. The 25kV inside a CRT is much less dangerous than 230VAC because the current is limited to under 5mA and the anode capacitance is under 100pF

I don't particularly care that they are not made anymore. I have a few CRT monitors that work really well and intend on using them because LCDs suck (you only get one resolution and that resolution isn't very high either). OK, well, I care a bit because I will have to use old monitors instead of being able to buy a new one, but it is not that big a deal.
While it may not be likely for a healthy adult to die from the anode cap, it still should hurt a lot and teach anyone about respecting devices high voltages.

[SoftwareSamurai]

American style plugs and switches are supposed to be taped around with electricans tape after the terminals have tightened and just prior to pushing them in their wall boxes ! but it is not mandatory, only recommended....

Uh...no. 

Electricians tape placed over the live terminals of a wall socket will not stop any appreciable amount of electricity from flowing into your fingers, down your arm, through your heart, and out your toes.
The only thing that will stop you from becoming the next electrically-cooked hotdog is to...turn off the power first!

Look, working with household electric wiring is really easy. There are only 3 rules:
1. Turn off the power.
2. Turn OFF the power!
3. TURN OFF THE POWER!

(If you doubt rule 1, see rule 2. If rule 2 seems silly, always follow rule 3.)

[Monkeh]

American style plugs and switches are supposed to be taped around with electricans tape after the terminals have tightened and just prior to pushing them in their wall boxes ! but it is not mandatory, only recommended....

Uh...no. 

Electricians tape placed over the live terminals of a wall socket will not stop any appreciable amount of electricity from flowing into your fingers, down your arm, through your heart, and out your toes.
The only thing that will stop you from becoming the next electrically-cooked hotdog is to...turn off the power first!

Look, working with household electric wiring is really easy. There are only 3 rules:
1. Turn off the power.
2. Turn OFF the power!
3. TURN OFF THE POWER!

(If you doubt rule 1, see rule 2. If rule 2 seems silly, always follow rule 3.)

It's not that I disagree with turning off the power, but I don't know what sort of tape you're thinking of, because mine will handle about 5kV per layer.

[SoftwareSamurai]

American style plugs and switches are supposed to be taped around with electricans tape after the terminals have tightened and just prior to pushing them in their wall boxes ! but it is not mandatory, only recommended....

Uh...no. 

Electricians tape placed over the live terminals of a wall socket will not stop any appreciable amount of electricity from flowing into your fingers, down your arm, through your heart, and out your toes.
The only thing that will stop you from becoming the next electrically-cooked hotdog is to...turn off the power first!

Look, working with household electric wiring is really easy. There are only 3 rules:
1. Turn off the power.
2. Turn OFF the power!
3. TURN OFF THE POWER!

(If you doubt rule 1, see rule 2. If rule 2 seems silly, always follow rule 3.)

It's not that I disagree with turning off the power, but I don't know what sort of tape you're thinking of, because mine will handle about 5kV per layer.

It's not the volts, it's the amps that kill.

A typical house line can supply between 15 to 20 amps before the breaker pops. (Assuming no GFCI breaker in line.) And let's not forget that we're made up of mostly water with lots of minerals and iron, which means we make a pretty good conductor. Yes, electrician's tape will prevent a direct connection between your fingers and pure death, but I guarantee you it won't stop an induced electrical shock. And if you're unlucky enough to be grounded in some way, that induced charge can easily stop your heart. So yes, the tape will probably save you from instantly discovering the afterlife, but I'm not about to assume the tape makes it safe to grab with the power on.

[MarkS]

It's not the volts, it's the amps that kill.

Myth.

[Monkeh]

It's not the volts, it's the amps that kill.

A typical house line can supply between 15 to 20 amps before the breaker pops. (Assuming no GFCI breaker in line.) And let's not forget that we're made up of mostly water with lots of minerals and iron, which means we make a pretty good conductor. Yes, electrician's tape will prevent a direct connection between your fingers and pure death, but I guarantee you it won't stop an induced electrical shock. And if you're unlucky enough to be grounded in some way, that induced charge can easily stop your heart. So yes, the tape will probably save you from instantly discovering the afterlife, but I'm not about to assume the tape makes it safe to grab with the power on.

I'd best stop touching all these flexible leads which are live, then. And no, it can supply a great deal more than that for the time required to harm someone.

Feel free to show me one case of a 120V or 240V (Which is what I handle live and dead quite regularly) cable inducing fatal current in someone through several layers of PVC tape with a breakdown voltage in excess of 40kV per mm.

And please remember that a shock does not equal death, and that GFCIs as you know them are not 100% reliable in operation nor in prevention of fatal shock.

[ejeffrey]

It's not the volts, it's the amps that kill.

Everyone who says this is wrong.  While the statement is technically true-ish, it is only quoted by people trying to defend an incorrect statement.

Yes, electrician's tape will prevent a direct connection between your fingers and pure death, but I guarantee you it won't stop an induced electrical shock.

I have no idea what you mean by induced electrical shock, but this is nonsense.  Electrical tape will protect you fine from a 230V/120V outlet.  The main problem with it is the danger that it can easily be pushed aside or come loose and allow a direct contact with the live wire.

[SoftwareSamurai]

It's not the volts, it's the amps that kill.

Myth.

<sigh> No, that's a fact. How else do you explain Tesla Coils? People touch "live" Tesla Coils and don't drop dead instantly. That's because a Tesla Coil generates high voltage, low current electricity.

[Monkeh]

It's not the volts, it's the amps that kill.

Myth.

<sigh> No, that's a fact. How else do you explain Tesla Coils? People touch "live" Tesla Coils and don't drop dead instantly. That's because a Tesla Coil generates high voltage, low current electricity.

I've touched live 240V wires and not dropped dead instantly. And no, not while totally isolated from ground. Tesla coils are still fully capable of doing potentially fatal damage to you.

[IanB]

<sigh> No, that's a fact. How else do you explain Tesla Coils? People touch "live" Tesla Coils and don't drop dead instantly. That's because a Tesla Coil generates high voltage, low current electricity.

No, it's a myth born out of an insufficient understanding of electricity. It gets tiring to keep hearing such a wrong headed statement.

There is more going on with Tesla coils than just low current. The high frequency has a lot to do with their properties. And don't ever delude yourself that Tesla coils are "safe". They can be incredibly dangerous if they are big and running at high power.

[Randall W. Lott]

It's not the volts, it's the amps that kill.

Myth.

<sigh> No, that's a fact. How else do you explain Tesla Coils? People touch "live" Tesla Coils and don't drop dead instantly. That's because a Tesla Coil generates high voltage, low current electricity.

Please watch this.  It explains exactly why it's not true.

[vk6zgo]

It's not the volts, it's the amps that kill.

Myth.

<sigh> No, that's a fact. How else do you explain Tesla Coils? People touch "live" Tesla Coils and don't drop dead instantly. That's because a Tesla Coil generates high voltage, low current electricity.

Please watch this.  It explains exactly why it's not true.

In general,this video "tells it like it is".

It's a bit unfortunate,though, that they show a CRT EHT connector with "Finger under here-dead!",as these supplies are most unlikely to cause a fatal injury.

EHT supplies of this kind are fairly well able to supply enough current for their normal load,but the application of an excessively low resistance load across them (like a person),causes their output to drop radically,so that the initial current is quite high,rapidly falling to a very much lower level.--In other words ,their REGULATION is quite poor.(Just another way of looking at high internal resistance).

You will find it extremely painful,you may have a heart attack,& if everything goes just right(or wrong ),it may give you a fatal shock!
I reiterate,however,it is very unlikely!

Another thing that freaks out a lot of people is that CRTs maintain a charge after the supply is off,& the EHT lead is removed.
Again,this residual charge is not dangerous,unless it makes you drop the CRT on your big toe !

(By the way,many computer people have the habit of calling the whole monitor a CRT,& produce a lot of crud about them,such as
"Your CRT has  umpteen pounds of lead in it!"
Anything about CRT monitors from computer sites should be treated with a very large "pinch of salt"!)

Back to our point:
If you were to start piddling around inside a 2KV DC supply in a radio transmitter,say,it's another story.
Lower voltage,much better regulation (lower internal resistance),designed to supply Amps of current!
You may well  be "sent to your reward",but no doubt will be gratified to know that the fatal current followed "Ohm's Law"!

About the insulating tape----it is INSULATING tape,& that is exactly what it does!
Many years ago,at work we tested  two layers of PVC tape,up to about 12-13kV,so it is pretty good!
Its main problem is that it is really only very good for wrapping around things where it can cover the whole of the conductive surface,with no gaps.
Wrapped around a large  power socket,it is quite difficult to obtain a really satisfactory wrap,so there may be gaps you could touch the "biteys" through!

 
 

[G7PSK]

I was told at school that it was possible to kill 500 people from the mains without blowing a 5 amp fuse if you got them all to hold hands, I am not sure if this is possible as I cannot find any reports of such an experiment being conducted.

I once got a nasty shock from a 2 volt lead acid battery when connecting the terminals up.

The maximum power allowed by law on an electric fence unit in the UK is 15 joules this is considered the maximum that will not be lethal to a normal person and I would assume that there is a safty factor there as well.

[Rerouter]

G7PSK, just as a baseline, nominal skin resistance limb to limb is about 12K,

lets say its a hot day,  everyones a little sweaty, that drags it down to about 8K,

stick 100 8K resistors in parrellel and you end up with about 3A on a 240V supply nominal, thats 30mA per person, which is lethal, even on 110V its 1.375A which is ~14mA per person, and a current that some could walk away from, but still capable to kill, and this is only looking at a 3A, 5A could kill a lot more people, though each leg would recieve around the same current,

if in series for 240V, 100 people on a good day only let 200uA pass, so even people with pacemakers would be safe

[cybergibbons]

It's not the volts, it's the amps that kill.

Myth.

<sigh> No, that's a fact. How else do you explain Tesla Coils? People touch "live" Tesla Coils and don't drop dead instantly. That's because a Tesla Coil generates high voltage, low current electricity.

One example of something not happening doesn't prove that it can never happen.

I don't get why there has to be a single mantra to deal with this. Fundamentally, only a small current is required through the chest to kill. It tends to require a high voltage to provide this current across a human body. Higher voltages are also more likely to cause secondary damage such as burns and entry/exit wounds that can also be fatal.

My take on the socket - I've replace probably several hundred damaged UK sockets in a school with damaged or cracked face plates over the course of 5 years. Sometimes they are badly damaged, but the socket stays in the wall and it's impossible to touch a live part without using an implement. The US sockets look like a child could touch the live terminal.